The Roles of Vitamin C in Skin Health

Abstract

The primary function of the skin is to act as a barrier against insults from the environment, and its unique structure reflects this. The skin is composed of two layers: the epidermal outer layer is highly cellular and provides the barrier function, and the inner dermal layer ensures strength and elasticity and gives nutritional support to the epidermis. Normal skin contains high concentrations of vitamin C, which supports important and well-known functions, stimulating collagen synthesis and assisting in antioxidant protection against UV-induced photodamage. This knowledge is often used as a rationale for the addition of vitamin C to topical applications, but the efficacy of such treatment, as opposed to optimising dietary vitamin C intake, is poorly understood. This review discusses the potential roles for vitamin C in skin health and summarises the in vitro and in vivo research to date. We compare the efficacy of nutritional intake of vitamin C versus topical application, identify the areas where lack of evidence limits our understanding of the potential benefits of vitamin C on skin health, and suggest which skin properties are most likely to benefit from improved nutritional vitamin C intake.

Full text

nutrients
Review
The Roles of Vitamin C in Skin Health
Juliet M. Pullar, Anitra C. Carr and Margreet C. M. Vissers *
Department of Pathology, University of Otago, Christchurch, P.O. Box 4345, Christchurch 8140, New Zealand;
juliet.pullar@otago.ac.nz (J.M.P.); anitra.carr@otago.ac.nz (A.C.C.)
*Correspondence: margreet.vissers@otago.ac.nz; Tel.: +64-3364-1524
Received: 10 July 2017; Accepted: 9 August 2017; Published: 12 August 2017
Abstract:
The primary function of the skin is to act as a barrier against insults from the environment,
and its unique structure reflects this. The skin is composed of two layers: the epidermal outer layer is
highly cellular and provides the barrier function, and the inner dermal layer ensures strength and
elasticity and gives nutritional support to the epidermis. Normal skin contains high concentrations of
vitamin C, which supports important and well-known functions, stimulating collagen synthesis and
assisting in antioxidant protection against UV-induced photodamage. This knowledge is often used
as a rationale for the addition of vitamin C to topical applications, but the efficacy of such treatment,
as opposed to optimising dietary vitamin C intake, is poorly understood. This review discusses
the potential roles for vitamin C in skin health and summarises the
in vitro
and
in vivo
research to
date. We compare the efficacy of nutritional intake of vitamin C versus topical application, identify
the areas where lack of evidence limits our understanding of the potential benefits of vitamin C on
skin health, and suggest which skin properties are most likely to benefit from improved nutritional
vitamin C intake.
Keywords:
ascorbate; dermis; epidermis; skin barrier function; vitamin C status; skin aging; wound
healing; collagen; UV protection
1. Introduction
The skin is a multi-functional organ, the largest in the body, and its appearance generally reflects
the health and efficacy of its underlying structures. It has many functions, but its fundamental role
is to provide a protective interface between the external environment and an individual’s tissues,
providing shielding from mechanical and chemical threats, pathogens, ultraviolet radiation and even
dehydration (functions reviewed in [
1
]). Being in constant contact with the external environment,
the skin is subject to more insults than most of our other organs, and is where the first visible signs of
aging occur.
The skin is composed of two main layers with quite different underlying structures—the
outermost epidermis and the deeper dermis (Figure 1). The epidermis fulfils most of the barrier
functions of the skin and is predominantly made up of cells, mostly keratinocytes [
2
]. The keratinocytes
are arranged in layers throughout the epidermis; as these cells divide and proliferate away from
the basal layer, which is closest to the dermis, they begin to differentiate. This process is called
keratinization, and involves the production of specialized structural proteins, secretion of lipids, and
the formation of a cellular envelope of cross-linked proteins. During differentiation, virtually all of
the subcellular organelles disappear, including the nucleus [
3
,
4
]. The cytoplasm is also removed,
although there is evidence that some enzymes remain [
4
]. Thus, the uppermost layer of the epidermis
that interacts with the outside environment is composed of flattened metabolically ‘dead’ cells (the
terminally differentiated keratinocytes). These cells are sealed together with lipid-rich domains,
forming a water-impermeable barrier. This layer is known as the stratum corneum (Figure 1) and fulfils
the primary barrier function of the epidermis, although the lower epidermal layers also contribute [
5
].
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Nutrients 2017,9, 866 2 of 27
Nutrients 2017, 9, 866 2 of 27
Figure 1. Micrograph of human breast skin sample, showing the full depth of the dermis (pink
staining) in comparison to the thin layer of epidermis (purple staining). The scale bar indicates 200
µm. A zoomed-in image is shown within the box. The stratum corneum, the outermost layer of the
epidermis, is indicated by the arrows, with its characteristic basket-weave structure. The collagen
bundles in the dermis are very clear, as are the scattered purple-stained fibroblasts that generate this
structure.
In contrast, the dermal skin layer provides strength and elasticity, and includes the vascular,
lymphatic and neuronal systems. It is relatively acellular and is primarily made up of complex
extracellular matrix proteins [6], being particularly rich in collagen fibres, which make up ~75% of
the dermis dry weight (Figure 1). The major cell type present in the dermis is fibroblasts, which are
heavily involved in the synthesis of many of the extracellular matrix components. Blood vessels that
supply nutrients to both skin layers are also present in the dermis [1,2]. Between the two main layers
is the dermal–epidermal junction, a specialised basement membrane structure that fixes the
epidermis to the dermis below.
2. Role of Nutrition in Skin Health
It is accepted that nutritional status with respect to both macronutrients and micronutrients is
important for skin health and appearance [7]. Evidence of this is provided by the many vitamin
deficiency diseases that result in significant disorders of the skin [8]. Dermatological signs of B
vitamin deficiency, for example, include a patchy red rash, seborrhoeic dermatitis and fungal skin
and nail infections [9,10]. The vitamin C deficiency disease scurvy is characterised by skin fragility,
bleeding gums and corkscrew hairs as well as impaired wound healing [11–18].
Nutritional status is vital for maintaining normal functioning of the skin during collagen
synthesis and keratinocyte differentiation [7]. Additionally, many of the components of our
antioxidant defences such as vitamins C and E and selenium are obtained from the diet, and these
are likely to be important for protection against UV-induced damage [19–23].
2.1. Nutrition Issues Specific to the Skin
The epidermis is a challenged environment for nutrient delivery, as it lacks the blood vessels
that normally deliver nutrients to cells. Delivery of nutrients is dependent on diffusion from the
vascularized dermis [24], and this may be particularly limited for the outermost layers of the
epidermis (Figure 2). Delivery is further compounded by the chemical nature of these outer
epidermal layers in which there is little movement of extracellular fluid between cells due to the
complex lipid/protein crosslink structure forming the skin barrier. All of this makes it likely that
dietary nutrients are not easily able to reach the cells in the outermost layers of the epidermis, and
these cells receive little nutrient support.
Figure 1.
Micrograph of human breast skin sample, showing the full depth of the dermis (pink
staining) in comparison to the thin layer of epidermis (purple staining). The scale bar indicates
200
µ
m. A zoomed-in image is shown within the box. The stratum corneum, the outermost layer of
the epidermis, is indicated by the arrows, with its characteristic basket-weave structure. The collagen
bundles in the dermis are very clear, as are the scattered purple-stained fibroblasts that generate
this structure.
In contrast, the dermal skin layer provides strength and elasticity, and includes the vascular,
lymphatic and neuronal systems. It is relatively acellular and is primarily made up of complex
extracellular matrix proteins [
6
], being particularly rich in collagen fibres, which make up ~75% of
the dermis dry weight (Figure 1). The major cell type present in the dermis is fibroblasts, which are
heavily involved in the synthesis of many of the extracellular matrix components. Blood vessels that
supply nutrients to both skin layers are also present in the dermis [
1
,
2
]. Between the two main layers
is the dermal–epidermal junction, a specialised basement membrane structure that fixes the epidermis
to the dermis below.
2. Role of Nutrition in Skin Health
It is accepted that nutritional status with respect to both macronutrients and micronutrients is
important for skin health and appearance [
7
]. Evidence of this is provided by the many vitamin
deficiency diseases that result in significant disorders of the skin [
8
]. Dermatological signs of B vitamin
deficiency, for example, include a patchy red rash, seborrhoeic dermatitis and fungal skin and nail
infections [
9
,
10
]. The vitamin C deficiency disease scurvy is characterised by skin fragility, bleeding
gums and corkscrew hairs as well as impaired wound healing [11–18].
Nutritional status is vital for maintaining normal functioning of the skin during collagen synthesis
and keratinocyte differentiation [
7
]. Additionally, many of the components of our antioxidant defences
such as vitamins C and E and selenium are obtained from the diet, and these are likely to be important
for protection against UV-induced damage [19–23].
Nutrition Issues Specific to the Skin
The epidermis is a challenged environment for nutrient delivery, as it lacks the blood vessels
that normally deliver nutrients to cells. Delivery of nutrients is dependent on diffusion from the
vascularized dermis [
24
], and this may be particularly limited for the outermost layers of the epidermis
(Figure 2). Delivery is further compounded by the chemical nature of these outer epidermal layers in
which there is little movement of extracellular fluid between cells due to the complex lipid/protein
crosslink structure forming the skin barrier. All of this makes it likely that dietary nutrients are not
easily able to reach the cells in the outermost layers of the epidermis, and these cells receive little
nutrient support.

Nutrients 2017,9, 866 3 of 27
Nutrients 2017, 9, 866 3 of 27
Figure 2. Delivery of nutrients to the skin. The location of the vitamin C transport proteins SVCT1
and SVCT2 are indicated. Red arrows depict nutrient flow from the blood vessels in the dermis to the
epidermal layer. Nutrients delivered by topical application would need to penetrate the barrier
formed by the stratum corneum.
The skin can be targeted for nutrient delivery through topical application (Figure 2). However,
in this case the delivery vehicle is influential, as the stratum corneum functions as an effective
aqueous barrier and prevents the passage of many substances [1]. Although some uncharged and
lipid-soluble molecules can pass through the surface layer, it is unlikely that nutrients delivered via
topical application would easily penetrate into the lower layers of the dermis [22]. The dermal layer
functions are therefore best supported by nutrients delivered through the bloodstream.
3. Vitamin C Content of Skin
Normal skin contains high concentrations of vitamin C, with levels comparable to other body
tissues and well above plasma concentrations, suggesting active accumulation from the circulation.
Most of the vitamin C in the skin appears to be in intracellular compartments, with concentrations
likely to be in the millimolar range [25–27]. It is transported into cells from the blood vessels present
in the dermal layer. Skin vitamin C levels have not often been reported and there is considerable
variation in the published levels, with a 10-fold range across a number of independent studies (Table
1). Levels are similar to that found in numerous other body organs. The variation in reported levels
most likely reflects the difficulty in handling skin tissue, which is very resilient to degradation and
solubilisation, but may also be due to the location of the skin sample and the age of the donor.
Table 1. Vitamin C content of human skin and a comparison with other tissues.
Tissue Vitamin C Content (mg/100 g Wet Weight) References
Adrenal glands 30–40 [28]
Pituitary glands 40–50 [29]
Liver 10–16 [28,30]
Spleen 10–15 [28,31]
Lungs 7 [28]
Kidneys 5–15 [30]
Heart muscle 5–15 [28,29,31]
Skeletal muscle 3–4 [29,32]
Brain 13–15 [28]
Skin-epidermis 6–64 [25–27]
Skin-dermis 3–13 [25–27]
Figure 2.
Delivery of nutrients to the skin. The location of the vitamin C transport proteins SVCT1
and SVCT2 are indicated. Red arrows depict nutrient flow from the blood vessels in the dermis to the
epidermal layer. Nutrients delivered by topical application would need to penetrate the barrier formed
by the stratum corneum.
The skin can be targeted for nutrient delivery through topical application (Figure 2). However,
in this case the delivery vehicle is influential, as the stratum corneum functions as an effective
aqueous barrier and prevents the passage of many substances [
1
]. Although some uncharged and
lipid-soluble molecules can pass through the surface layer, it is unlikely that nutrients delivered via
topical application would easily penetrate into the lower layers of the dermis [
22
]. The dermal layer
functions are therefore best supported by nutrients delivered through the bloodstream.
3. Vitamin C Content of Skin
Normal skin contains high concentrations of vitamin C, with levels comparable to other body
tissues and well above plasma concentrations, suggesting active accumulation from the circulation.
Most of the vitamin C in the skin appears to be in intracellular compartments, with concentrations
likely to be in the millimolar range [
25
–
27
]. It is transported into cells from the blood vessels present in
the dermal layer. Skin vitamin C levels have not often been reported and there is considerable variation
in the published levels, with a 10-fold range across a number of independent studies (Table 1). Levels
are similar to that found in numerous other body organs. The variation in reported levels most likely
reflects the difficulty in handling skin tissue, which is very resilient to degradation and solubilisation,
but may also be due to the location of the skin sample and the age of the donor.
Table 1. Vitamin C content of human skin and a comparison with other tissues.
Tissue Vitamin C Content (mg/100 g Wet Weight) References
Adrenal glands 30–40 [28]
Pituitary glands 40–50 [29]
Liver 10–16 [28,30]
Spleen 10–15 [28,31]
Lungs 7 [28]
Kidneys 5–15 [30]
Heart muscle 5–15 [28,29,31]
Skeletal muscle 3–4 [29,32]
Brain 13–15 [28]
Skin-epidermis 6–64 [25–27]
Skin-dermis 3–13 [25–27]

Nutrients 2017,9, 866 4 of 27
Several reports have indicated that vitamin C levels are lower in aged or photodamaged
skin
[25–27]
. Whether this association reflects cause or effect is unknown, but it has also been
reported that excessive exposure to oxidant stress via pollutants or UV irradiation is associated
with depleted vitamin C levels in the epidermal layer [
33
,
34
]. Indeed, more vitamin C is found in
the epidermal layer than in the dermis, with differences of 2–5-fold between the two layers being
consistently reported (Table 1and [
25
,
26
]). Levels of vitamin C in skin are similar to the levels of other
water soluble antioxidants such as glutathione [25–27,35]. There is a suggestion that vitamin C in the
stratum corneum layer of the epidermis exists in a concentration gradient [36]. The lowest vitamin C
concentration was present at the outer surface of the epidermis of the SKH-1 hairless mouse, a model
of human skin, with a sharp increase in concentration in the deeper layers of the stratum corneum,
possibly reflecting depletion in the outer cells due to chronic exposure to the environment [36].
3.1. The Bioavailability and Uptake of Vitamin C into the Skin
3.1.1. The Sodium-Dependent Vitamin C Transporters
Vitamin C uptake from the plasma and transport across the skin layers is mediated by specific
sodium-dependent vitamin C transporters (SVCTs) that are present throughout the body and are also
responsible for transport into other tissues. Interestingly, cells in the epidermis express both types
of vitamin C transporter, SVCT1 and SVCT2 (Figure 2) [
37
]. This contrasts with most other tissues,
which express SVCT2 only [
37
–
39
]. SVCT1 expression in the body is largely confined to the epithelial
cells in the small intestine and the kidney and is associated with active inter-cellular transport of the
vitamin [
40
,
41
]. The specific localisation of SVCT1 in the epidermis is of interest due to the lack of
vasculature in this tissue, and suggests that the combined expression of both transporters 1 and 2
ensures effective uptake and intracellular accumulation of the vitamin. Together with the high levels
of vitamin C measured in the epidermal layer, the dual expression of the SVCTs suggests a high
dependency on vitamin C in this tissue.
Both transporters are hydrophobic membrane proteins that co-transport sodium, driving the
uptake of vitamin C into cells. Replacement of sodium with other positively charged ions completely
abolishes transport [
42
]. SVCT1 and SVCT2 have quite different uptake kinetics reflecting their
different physiological functions. SVCT1 transports vitamin C with a low affinity but with a high
capacity (K
m
of 65–237
µ
mol/L) mediating uptake of vitamin C from the diet and re-uptake in the
tubule cells in the kidney [
41
]. SVCT2, which is present in almost every cell in the body, is thought
to be a high-affinity, low capacity transporter, with a K
m
of ~20
µ
M meaning it can function at low
concentrations of vitamin C [
41
]. As well as transporter affinity, vitamin C transport is regulated by
the availability of the SVCT proteins on the plasma membrane.
3.1.2. Bioavailability and Uptake
Most tissues of the body respond to plasma availability of vitamin C and concentrations vary
accordingly, with lower tissue levels being reported when plasma levels are below saturation [
43
–
47
].
The kinetics of uptake varies between tissues, with vitamin C levels in some organs (e.g., the brain)
reaching a plateau at lower plasma vitamin C status, whereas other tissue levels (e.g., skeletal muscle)
continue to increase in close association with increasing plasma supply [32,44,45,48].
Very little is known about vitamin C accumulation in the skin and there are no studies that have
investigated the relationship between skin vitamin C content and nutrient intake or plasma supply.
Two human studies have shown an increase in skin vitamin C content following supplementation with
vitamin C, but neither contained adequate measures of plasma vitamin C levels in the participants
before or after supplementation [
27
,
49
]. In one other study, vitamin C content was measured in
buccal keratinocytes, as these cells are proposed to be a good model for skin keratinocytes [
50
].
The keratinocyte vitamin C concentration doubled upon supplementation of the participants with

Nutrients 2017,9, 866 5 of 27
3 g/day vitamin C for six weeks, a dosage that is significantly higher than the recommended daily
intake and would achieve plasma saturation and likely also tissue saturation [44].
Thus it appears likely that, as with many other tissues, skin vitamin C levels respond to increases
in plasma supply [
27
,
50
]. A paper by Nusgens and co-workers suggests that skin levels do not increase
further once plasma saturation is reached [
51
]. Dietary supplementation is therefore only expected to
be effective in elevating skin vitamin C in individuals who have below-saturation plasma levels prior
to intervention.
3.1.3. Topical Application of Vitamin C
When plasma levels are low, some vitamin C can be delivered to the epidermal layer by topical
application, although the efficacy of this is dependent on the formulation of the cream or serum
used on the skin [
51
–
55
]. Vitamin C, as a water-soluble and charged molecule, is repelled by the
physical barrier of the terminally differentiated epidermal cells. It is only when pH levels are below
4 and vitamin C is present as ascorbic acid that some penetration occurs [
56
], but whether this results
in increased levels in the metabolically compromised stratum corneum is unknown. A great deal
of effort has been put into the development of ascorbic acid derivatives for the purpose of topical
application. Such derivatives need to ensure stabilization of the molecule from oxidation and also
overcome the significant challenge of skin penetration. In addition, they must be converted to ascorbic
acid
in vivo
in order to be effective. Whether there is a single solution to all these challenges is
unclear [
57
]. The addition of a phosphate group confers greater stability and these derivatives may be
converted to ascorbic acid
in vivo
, albeit at a slow rate [
58
], but they are poorly absorbed through the
skin [
56
,
59
,
60
]. Ascorbyl glucoside also exhibits superior stability and can penetrate, but the rate of
its
in vivo
conversion is not known [
57
,
61
–
63
]. Derivatives containing lipid-soluble moieties such as
palmitate are designed to assist with delivery, and although increased uptake has been demonstrated
in animals [
64
], they do not necessarily show improved stability and there is some doubt as to whether
these derivatives are efficiently converted
in vivo
[
57
]. Recent studies suggest that encapsulation into
a lipospheric form may assist with transport into the lower layers of the epidermis and could result
in increased uptake [
65
–
67
]. However, the most pertinent issue for the efficacy of topical application
is likely to be the plasma status of the individual: if plasma levels are saturated, then it appears that
topical application does not increase skin vitamin C content [51].
3.1.4. Vitamin C Deficiency
One of the most compelling arguments for a vital role for vitamin C in skin health is the association
between vitamin C deficiency and the loss of a number of important skin functions. In particular,
poor wound healing (associated with collagen formation), thickening of the stratum corneum and
subcutaneous bleeding (due to fragility and loss of connective tissue morphology) are extreme and
rapid in onset in vitamin-C-deficient individuals [
11
,
15
–
18
]. It is thought that similar processes occur
when body stores are below optimal, although to a lesser extent [46,68].
4. Potential Functions of Vitamin C in the Skin
The high concentration of vitamin C in the skin indicates that it has a number of important
biological functions that are relevant to skin health. Based on what we know about vitamin C function,
attention has been focused on collagen formation and antioxidant protection; however, evidence is
emerging for other activities.
4.1. The Promotion of Collagen Formation
Vitamin C acts as a co-factor for the proline and lysine hydroxylases that stabilise the collagen
molecule tertiary structure, and it also promotes collagen gene expression [
69
–
77
]. In the skin, collagen
formation is carried out mostly by the fibroblasts in the dermis, resulting in the generation of the
basement membrane and dermal collagen matrix (Figure 3) [
75
,
78
]. The dependence of the collagen

Nutrients 2017,9, 866 6 of 27
hydroxylase enzymes on vitamin C has been demonstrated in a number of studies with fibroblast
cells
in vitro
[
69
,
73
,
79
], with both decreased total synthesis and decreased crosslinking when vitamin
C is absent [
80
–
82
]. The activity of the hydroxylases is much more difficult to measure
in vivo
,
as the amount of collagen synthesised may vary only a little [
51
,
52
]. Rather, animal studies with
the vitamin-C-deficient GULO mouse indicate that the stability of the synthesised collagen varies
with vitamin C availability, reflecting the stabilising function of the collagen crosslinks formed by the
hydroxylases [
76
]. In addition to stabilising the collagen molecule by hydroxylation, vitamin C also
stimulates collagen mRNA production by fibroblasts [78,83].
Nutrients 2017, 9, 866 6 of 27
in vivo, as the amount of collagen synthesised may vary only a little [51,52]. Rather, animal studies
with the vitamin-C-deficient GULO mouse indicate that the stability of the synthesised collagen
varies with vitamin C availability, reflecting the stabilising function of the collagen crosslinks formed
by the hydroxylases [76]. In addition to stabilising the collagen molecule by hydroxylation, vitamin
C also stimulates collagen mRNA production by fibroblasts [78,83].
Figure 3. Structure of the dermis. Higher magnification of H&E-stained dermis, showing the irregular
nature of the bundled collagen fibres (pink stained) and sparse presence of the fibroblasts (blue
nuclear staining). Vitamin C present in the fibroblasts supports the synthesis of the collagen fibres.
4.2. The Ability to Scavenge Free Radicals and Dispose of Toxic Oxidants
Vitamin C is a potent antioxidant that can neutralise and remove oxidants, such as those found
in environmental pollutants and after exposure to ultraviolet radiation. This activity appears to be of
particular importance in the epidermis, where vitamin C is concentrated in the skin. However,
vitamin C is only one player in the antioxidant arsenal that includes enzymatic defences (catalase,
glutathione peroxidase and superoxide dismutase) as well as other non-enzymatic defences (vitamin
E, glutathione, uric acid and other putative antioxidants such as carotenoids) [19,21,33,34,84–88].
Most intervention studies carried out to determine the capacity of antioxidants to prevent oxidative
damage to skin have used a cocktail of these compounds [21,88–90]. Vitamin C is particularly
effective at reducing oxidative damage to the skin when it is used in conjunction with vitamin E
[21,54,89,91,92]. This is in accord with its known function as a regenerator of oxidised vitamin E,
thereby effectively recycling this important lipid-soluble radical scavenger and limiting oxidative
damage to cell membrane structures [92,93] (Figure 4).
Figure 3.
Structure of the dermis. Higher magnification of H&E-stained dermis, showing the irregular
nature of the bundled collagen fibres (pink stained) and sparse presence of the fibroblasts (blue nuclear
staining). Vitamin C present in the fibroblasts supports the synthesis of the collagen fibres.
4.2. The Ability to Scavenge Free Radicals and Dispose of Toxic Oxidants
Vitamin C is a potent antioxidant that can neutralise and remove oxidants, such as those found in
environmental pollutants and after exposure to ultraviolet radiation. This activity appears to be of
particular importance in the epidermis, where vitamin C is concentrated in the skin. However, vitamin
C is only one player in the antioxidant arsenal that includes enzymatic defences (catalase, glutathione
peroxidase and superoxide dismutase) as well as other non-enzymatic defences (vitamin E, glutathione,
uric acid and other putative antioxidants such as carotenoids) [
19
,
21
,
33
,
34
,
84
–
88
]. Most intervention
studies carried out to determine the capacity of antioxidants to prevent oxidative damage to skin have
used a cocktail of these compounds [
21
,
88
–
90
]. Vitamin C is particularly effective at reducing oxidative
damage to the skin when it is used in conjunction with vitamin E [
21
,
54
,
89
,
91
,
92
]. This is in accord with
its known function as a regenerator of oxidised vitamin E, thereby effectively recycling this important
lipid-soluble radical scavenger and limiting oxidative damage to cell membrane structures [
92
,
93
]
(Figure 4).

Nutrients 2017,9, 866 7 of 27
Nutrients 2017, 9, 866 7 of 27
Figure 4. The central role for vitamin C and other antioxidants pertinent to the skin. The
interdependence of vitamins E and C, and glutathione, in the scavenging of free radicals and
regeneration of the reduced antioxidants, is shown. Vitamin E is in the lipid fraction of the cell,
whereas vitamin C and glutathione are water-soluble and present in the cytosol.
4.3. Inhibition of Melanogenesis
Vitamin C derivatives, including the magnesium phosophate ascorbyl derivative, have been
shown to decrease melanin synthesis both in cultured melanocytes and in vivo [94,95]. This activity
has been proposed to be due to its ability to interfere with the action of tyrosinase, the rate-limiting
enzyme in melanogenesis. Tyrosinase catalyses the hydroxylation of tyrosine to
dihydroxyphenylalanine (DOPA), and the oxidation of DOPA to its corresponding ortho-quinone.
The inhibition in melanin production by vitamin C is thought to be due to the vitamin’s ability to
reduce the ortho-quinones generated by tyrosinase [94], although other mechanisms are also possible
[96]. Agents that decrease melanogenesis are used to treat skin hyperpigmentation in conditions such
as melisma or age spots.
4.4. Interaction with Cell Signalling Pathways
In vitro studies clearly show that vitamin C can play a role in the differentiation of keratinocytes
(Table 2). For example, vitamin C enhanced the differentiation of rat epidermal keratinocytes cells in
an organotypic culture model [97], with markedly improved ultrastructural organisation of the
stratum corneum, accompanied by enhanced barrier function. Vitamin C also increased numbers of
keratohyalin granules and levels of the late differentiation marker filaggrin, which appeared to be
due to altered gene expression [97]. Others have also shown that vitamin C promotes synthesis and
organization of barrier lipids and increased cornified envelope formation during differentiation
[98–102]. The mechanism(s) by which vitamin C modulates keratinocyte differentiation is not yet
elucidated; however, it has been hypothesized to be under the control of protein kinase C and AP-1
[99].
In addition to vitamin C’s ability to promote collagen synthesis [73,79], there is evidence to
suggest that vitamin C increases proliferation and migration of dermal fibroblasts [78,82,102],
functions vital for effective wound healing, although the underlying mechanisms driving this activity
are not yet known [78]. Through the stimulation of regulatory hydroxylases, vitamin C also regulates
the stabilization and activation of the hypoxia-inducible factor (HIF)-1, a metabolic sensor that
controls the expression of hundreds of genes involved with cell survival and tissue remodelling,
including collagenases [103–105]. Vitamin C has been shown to both stimulate [69] and inhibit elastin
synthesis in cultured fibroblasts [81]. Glycosaminoglycan synthesis as part of extracellular matrix
formation is also increased by vitamin C treatment [106], and it may also influence gene expression
of antioxidant enzymes, including those involved in DNA repair [78]. As such, vitamin C has been
shown to increase the repair of oxidatively damaged bases. [78]. The modulation of gene expression
Figure 4.
The central role for vitamin C and other antioxidants pertinent to the skin. The interdependence
of vitamins E and C, and glutathione, in the scavenging of free radicals and regeneration of the reduced
antioxidants, is shown. Vitamin E is in the lipid fraction of the cell, whereas vitamin C and glutathione
are water-soluble and present in the cytosol.
4.3. Inhibition of Melanogenesis
Vitamin C derivatives, including the magnesium phosophate ascorbyl derivative, have been
shown to decrease melanin synthesis both in cultured melanocytes and
in vivo
[
94
,
95
]. This activity has
been proposed to be due to its ability to interfere with the action of tyrosinase, the rate-limiting enzyme
in melanogenesis. Tyrosinase catalyses the hydroxylation of tyrosine to dihydroxyphenylalanine
(DOPA), and the oxidation of DOPA to its corresponding ortho-quinone. The inhibition in melanin
production by vitamin C is thought to be due to the vitamin’s ability to reduce the ortho-quinones
generated by tyrosinase [
94
], although other mechanisms are also possible [
96
]. Agents that decrease
melanogenesis are used to treat skin hyperpigmentation in conditions such as melisma or age spots.
4.4. Interaction with Cell Signalling Pathways
In vitro
studies clearly show that vitamin C can play a role in the differentiation of keratinocytes
(Table 2). For example, vitamin C enhanced the differentiation of rat epidermal keratinocytes cells
in an organotypic culture model [
97
], with markedly improved ultrastructural organisation of the
stratum corneum, accompanied by enhanced barrier function. Vitamin C also increased numbers
of keratohyalin granules and levels of the late differentiation marker filaggrin, which appeared
to be due to altered gene expression [
97
]. Others have also shown that vitamin C promotes
synthesis and organization of barrier lipids and increased cornified envelope formation during
differentiation
[98–102]
. The mechanism(s) by which vitamin C modulates keratinocyte differentiation
is not yet elucidated; however, it has been hypothesized to be under the control of protein kinase C
and AP-1 [99].
In addition to vitamin C’s ability to promote collagen synthesis [
73
,
79
], there is evidence to
suggest that vitamin C increases proliferation and migration of dermal fibroblasts [
78
,
82
,
102
], functions
vital for effective wound healing, although the underlying mechanisms driving this activity are not
yet known [
78
]. Through the stimulation of regulatory hydroxylases, vitamin C also regulates the
stabilization and activation of the hypoxia-inducible factor (HIF)-1, a metabolic sensor that controls
the expression of hundreds of genes involved with cell survival and tissue remodelling, including
collagenases [
103
–
105
]. Vitamin C has been shown to both stimulate [
69
] and inhibit elastin synthesis
in cultured fibroblasts [
81
]. Glycosaminoglycan synthesis as part of extracellular matrix formation is
also increased by vitamin C treatment [
106
], and it may also influence gene expression of antioxidant
enzymes, including those involved in DNA repair [
78
]. As such, vitamin C has been shown to increase
the repair of oxidatively damaged bases. [
78
]. The modulation of gene expression may be important

Nutrients 2017,9, 866 8 of 27
for its ability to protect during UV exposure via its inhibition of pro-inflammatory cytokine secretion
and apoptosis [107–109].
4.5. Modulation of Epigenetic Pathways
In addition to the gene regulatory activities listed above, vitamin C has a role in epigenetic
regulation of gene expression by functioning as a co-factor for the ten-eleven translocation (TET)
family of enzymes, which catalyse the removal of methylated cytosine through its hydroxylation to
5-hydroxymethylcytosine (5 hmC) [
110
–
112
]. As well as being a DNA demethylation intermediate, it
appears that 5 hmC is an epigenetic mark in its own right, with transcriptional regulatory activity [
113
].
Aberrant epigenetic alterations are thought to have a role in cancer progression, and there is data to
suggest that a loss of 5 hmC occurs during the early development and progression of melanoma [
114
].
Interestingly, vitamin C treatment has been shown to increase 5 hmC content in melanoma cell lines,
also causing a consequent alteration in the transcriptome and a decrease in malignant phenotype [
115
].
Because TETs have a specific requirement for vitamin C to maintain enzyme activity [
116
], this provides
a further mechanism by which the vitamin may affect gene expression and cell function. For example,
Lin and co-workers showed that vitamin C protected against UV-induced apoptosis of an epidermal cell
line via a TET-dependent mechanism, which involved increases in p21 and p16 gene expression [
117
].
Table 2. Summary of key in vitro studies investigating potential effects of vitamin C on the skin.
Study Description Measured Parameters Outcome and Comment Reference
Effects on collagen and elastin synthesis
Vit. C effects on collagen and
elastin synthesis in human skin
fibroblasts and vascular smooth
muscle cells.
Monitored vit. C time of exposure
and dose on collagen synthesis
and gene expression, and elastin
synthesis and gene regulation.
Vit. C exposure increased collagen,
decreased elastin. Stabilization of
collagen mRNA, lesser stability of
elastin mRNA, and repression of
elastin gene transcription.
[81]
Effect of vit. C on collagen
synthesis and SVCT2 expression
in human skin fibroblasts. Vit. C
added to culture medium for
5 days.
Vit. C uptake measured into cells,
collagen I and IV measured with
RT-PCR and ELISA, and RT-PCR
for SVCT2.
Vit. C increased collagen I and IV,
and increased SVCT2 expression. [73]
Effect of vit. C on elastin
generation by fibroblasts from
normal human skin,
stretch-marked skin, keloids and
dermal fat.
Immunohistochemistry and
western blotting for detection of
elastin and precursors.
50 and 200 µM vit. C increased
elastin production, 800 µM
inhibited. No measures of vit. C
uptake into cells.
[69]
Effects on morphology, differentiation and gene expression
Vit. C addition to cultures of rat
keratinocytes (REK).
Effect on differentiation and
stratum corneum formation.
Morphology showed enhanced
stratum corneum structure,
increased keratohyalin granules and
organization of intercellular lipid
lamellae in the interstices of the
stratum corneum. Increased
profilaggrin and filaggrin.
[97]
Effect of vit. C on human
keratinocyte (HaCaT) cell line
differentiation in vitro.
Measured development of
cornified envelope (CE),
gene expression.
CE formation and keratinocyte
differentiation induced by vit. C,
suggesting a role in formation of
stratum corneum and barrier
formation in vivo.
[99]
Effect of vit. C supplementation
on gene expression in human
skin fibroblasts.
Total RNA nano assay, for genetic
profiling, with and without vit. C
in culture medium.
Increased gene expression for DNA
replication and repair and cell cycle
progression. Increased mitogenic
stimulation and cell motility in the
context of wound healing. Faster
repair of damaged DNA bases.
[78]

Nutrients 2017,9, 866 9 of 27
Table 2. Cont.
Study Description Measured Parameters Outcome and Comment Reference
Effect of vit. C on dermal
epidermal junction in skin model
(keratinocytes and fibroblasts).
Keratinocyte organisation,
fibroblast number, basement
membrane protein deposition and
mRNA expression.
Vit. C improved keratinocyte and
basement membrane organisation.
Increased fibroblast number, saw
deposition of basement
membrane proteins.
[102]
Effect of vit. C on cultured skin
models—combined human
epidermal keratinocytes and
dermal fibroblasts.
Monitored morphology, lipid
composition.
Vit. C, but not vit. E, improved
epidermal morphology, ceramide
production and phospholipid
layer formation.
[98]
Protective effects against UV irradiation
Effect of vit. C on UVA irradiation
of primary cultures of human
keratinocytes.
Vit. C added in low
concentrations, monitored MDA,
TBA, GSH, cell viability, IL-1,
IL-6 generation.
Vit. C improved resistance to UVA,
decreased MDA and TBA levels,
increased GSH levels, decreased
IL-1 and IL-6 levels.
[109]
Effect of vit. C uptake into human
keratinocyte (HaCaT) cell line on
outcome to UV irradiation.
Accumulation of vit. C in
keratinocytes, antioxidant
capacity by DHDCF and apoptosis
induction by UV irradiation.
Keratinocytes accumulated mM
levels of vit. C, increasing
antioxidant status and protecting
against apoptosis.
[108]
Effect of UVB on vit. C uptake
into human keratinocyte cell line
(HaCaT) and effects on
inflammatory gene expression.
Cellular vit. C measured by
HPLC, mRNA expression for
chemokines, western blotting for
SVCT localisation.
Vit. C uptake was increased with
UVB irradiation, chemokine
expression decreased with
vit. C uptake.
[107]
Protective effects against ozone exposure
Effect of antioxidant mixtures of
vit. C, vit. E and ferulic acid on
exposure of cultured normal
human keratinocytes to ozone.
Cell viability, proliferation, HNE,
protein carbonyls, Nrf2,
NFkappaB activation,
IL-8 generation.
Vit. C-containing mixtures inhibited
toxicity. The presence of vit. E
provided additional protection
against HNE and protein carbonyls.
[118]
Protection of cultured skin cells
against ozone exposure with vit.
C, vit. E, and resveratrol. 3-D
culture of human
dermis—fibroblasts with collagen
I + III.
Cell death, HNE levels, expression
of transcription factors Nrf-2 and
NfkappaB
Extensive protection against cell
damage with mixtures containing
vit. C. Increased expression of
antioxidant proteins. Additional
effect of vit. E + C. No effect with
Vit. E alone.
[119]
5. Challenges to the Maintenance of Skin Health and Potential Protection by Vitamin C
During the course of a normal lifetime, the skin is exposed to a number of challenges that can
affect structure, function and appearance, including:
•Deterioration due to normal aging, contributing to loss of elasticity and wrinkle formation.
•Exposure to the elements, leading to discolouration, dryness and accelerated wrinkling.
•
Chemical insults including exposure to oxidising beauty and cleansing products (hair dyes, soaps,
detergents, bleaches).
•Direct injury, as in wounding and burning.
Vitamin C may provide significant protection against these changes and regeneration of healthy
skin following insult and injury is a goal for most of us. The following sections, and the summary in
Tables 3and 4, review the available evidence of a role for vitamin C in the maintenance of healthy skin
and the prevention of damage.
5.1. Skin Aging
Like the rest of the human body, the skin is subject to changes caused by the process of natural
aging. All skin layers show age-related changes in structure and functional capacity [
6
,
120
] and,
as occurs in other body systems, this may result in increased susceptibility to a variety of disorders
and diseases, such as the development of dermatoses and skin cancer [
6
,
22
,
121
,
122
]. As well as this,

Nutrients 2017,9, 866 10 of 27
changes in the appearance of skin are often the first visible signs of aging and this can have implications
for our emotional and mental wellbeing.
Aging of skin can be thought of as two distinct processes—natural or ‘intrinsic’ aging, caused
simply by the passage of time, and environmental aging [
121
,
123
,
124
]. Lifestyle factors such as
smoking and exposure to environmental pollutants increase the rate of environmental aging, and
can have a marked impact on the function and appearance of skin [
22
,
121
–
124
]. Exposure to chronic
ultraviolet radiation from sunlight is also a major environmental factor that prematurely damages our
skin (effects are detailed in the photoaging section below) [
125
]. The changes due to environmental
aging are usually superimposed on those that occur naturally, often making it difficult to distinguish
between the two [22].
Intrinsic aging is a slow process and, in the absence of environmental aging, changes are not
usually apparent until advanced age, when smooth skin with fine wrinkles, pale skin tone, reduced
elasticity, and occasional exaggerated expression lines are evident [
6
,
22
,
24
]. There is a reduction in the
thickness of the dermal layer [
22
], along with fewer fibroblasts and mast cells, less collagen production
and reduced vascularisation [
24
]. Specifically, during intrinsic aging there is gradual degradation of
the extracellular matrix components, particularly elastin and collagen [
124
,
126
]. The loss of elastin
results in the reduction in elasticity and capacity for recoil that is observed in aging skin.
Dry skin is very common in older adults [
127
], largely due to a loss of glycosaminoglycans and
accompanied reduction in the ability to maintain moisture levels [
126
,
128
]. The dermal-epidermal
junction may also become flattened, losing surface area and leading to increased skin fragility [
22
],
and potentially causing reduced nutrient transfer between the two layers. In general, the dermis
suffers from greater age-related changes than the epidermis [
1
]. However, the aged epidermis shows a
reduced barrier function and also reduced repair following insult [
6
]. Antioxidant capacity, immune
function and melanin production may also be impaired in aged skin [22].
Intrinsic aging is largely unavoidable and may be largely dependent on our genetic background
and other factors [129,130]. Some mitigation of these effects may be achieved by:
•
Limiting exposure to environmental risk factors such as smoking, poor nutrition and chronic
exposure to sunlight, which cause premature skin aging.
•
Using treatments to potentially reverse skin damage, including topical or systemic treatments
that help regenerate the elastic fibre system and collagen [126].
5.1.1. The Role of Vitamin C in the Prevention of Skin Aging
The ability of vitamin C to limit natural aging is difficult to distinguish from its ability to prevent
the additional insults due to excessive sun exposure, smoking or environmental stress and there is very
limited information available concerning a relationship between vitamin C levels and general skin
deterioration. The most compelling argument for a role of vitamin C in protecting skin function comes
from observations that deficiency causes obvious skin problems—early signs of scurvy, for example,
include skin fragility, corkscrew hairs and poor wound healing [11–17].
Because vitamin C deficiency results in impaired function, it is assumed that increasing intake
will be beneficial. However, there are no studies that have measured vitamin C levels or intake and
associated aging changes [
130
]. Vitamin C is almost never measured in the skin and this information is
needed before we can improve our understanding of what level of intake might be beneficial for skin
health and protection against aging-related changes.
5.1.2. Nutritional Studies Linking Vitamin C with Skin Health
Although there is no information specific to vitamin C and aging in the skin, many studies have
attempted to determine the role of nutrition more generally [
85
,
131
–
133
]. A recent systematic review of
studies involving nutrition and appearance identified 27 studies that were either dietary intervention
studies or reported dietary intakes [
134
]. The analysis indicated that, in the most reliable studies,

Nutrients 2017,9, 866 11 of 27
intervention with a nutrient supplement (15 studies) or general foods (one study) was associated
with improved measures of skin elasticity, facial wrinkling, roughness and colour [
134
]. Many of the
nutrient interventions that showed a benefit included a high intake of fruit and vegetables, which
contribute significant levels of vitamin C to the diet.
A double-blind nutrition intervention study has evaluated the effects of dietary supplementation
with a fermented papaya extract, thought to have antioxidant activity [
135
], and an antioxidant
cocktail containing 10 mg trans resveratrol, 60
µ
g selenium, 10 mg vitamin E and 50 mg vitamin C
in a population of healthy individuals aged between 40 and 65, all with visible signs of skin aging.
Following a 90-day supplementation period, skin surface, brown spots, evenness, moisture, elasticity
(face), lipid peroxidation markers, superoxide dismutase activity, nitric oxide (NO) concentration, and
the expression levels of key genes were measured. Notably, the intervention resulted in a measureable
improvement in skin physical parameters, with a generally enhanced response from the fermented
papaya extract compared with the antioxidant cocktail. Gene expression, measured by RNA extraction
and RT-PCR, indicated that the papaya extract increased expression of aquaporin-3, and decreased
expression of cyclophilin A and CD147. Aquaporin 3 regulates water transport across the lipid
bilayer in keratinocytes and fibroblasts and therefore improves skin health [
136
]; cyclophilin A and
the transmembrane glycoprotein CD147 negatively impact on skin DNA repair mechanisms and
affect the inflammatory response, therefore negatively impacting skin health. This is an interesting
study and suggests that antioxidant supplementation, including vitamin C, could benefit skin health
generally. The antioxidant cocktail did not affect gene expression, and this may reflect the low
concentrations of each component in the supplement, which is unlikely to influence levels in a healthy
population. Although there were no direct measures to determine whether antioxidant status was
actually improved in the participants, antioxidant activity was improved in the skin following intake of
the papaya extract, as evidenced by decreased markers of lipid peroxidation and increased superoxide
dismutase activity.
5.2. UV Radiation and Photoaging
There is mounting evidence to suggest that the most significant environmental challenge to the
skin is chronic exposure to ultraviolet radiation from the sun or from tanning beds [
22
,
90
,
123
,
137
].
UV radiation damages skin through the production of reactive oxygen species, which can damage the
extracellular matrix components and affect both the structure and function of cells. While the skin
contains endogenous antioxidant defences, vitamins E and C and antioxidant enzymes to quench these
oxidants and repair the resultant damage, these antioxidants will be consumed by repeated exposure
and the skin’s defences can thereby be overwhelmed [25,138–141].
Acute exposure of skin to UV radiation can cause sunburn, resulting in a large inflammatory
response causing characteristic redness, swelling and heat. In addition, altered pigmentation,
immune suppression and damage to the dermal extracellular matrix can occur [
24
,
25
,
56
,
142
,
143
].
By comparison, chronic long-term exposure to UV radiation causes premature aging of the skin,
with dramatic and significant disruption to skin structure, and leads to the development of skin
cancer [
6
,
24
]. Termed photoaging, the most obvious features are wrinkles, hyperpigmentation and
marked changes in skin elasticity that cause skin sagging, with the skin also becoming sallow and
rougher with age [
123
,
144
]. Photoaged skin is most likely to be found on the face, chest and upper
surface of the arms.
Both the epidermal and dermal layers of skin are susceptible to chronic UV exposure; however,
the most profound changes occur in the extracellular matrix of the dermis [
24
]. Changes include
a significant loss of collagen fibrils within the dermis, but also specific loss of collagen anchoring
fibrils at the dermal–epidermal junction [
126
]. Dermal glycosaminoglycan content is increased in what
appear to be disorganised aggregates [
126
]. Elastic fibres throughout the dermis are also susceptible to
UV radiation, with accumulation of disorganised elastic fibre proteins evident in severely photoaged
skin. Indeed, this accumulation, termed ‘solar elastosis’, is considered to be a defining characteristic

Nutrients 2017,9, 866 12 of 27
of severely photoaged skin [
6
,
22
,
24
,
126
]. There is also evidence of epidermal atrophy or ‘wasting
away’ during photoaging, and of a reduction in the barrier function [
6
]. In addition, the epidermis
can become hyperpigmented from chronic UV exposure; these lesions are known as age spots or
liver spots.
Preventing exposure to UV radiation is the best means of protecting the skin from the detrimental
effects of photoaging. However, avoidance is not always possible, so sunscreen is commonly used
to block or reduce the amount of UV reaching the skin. However, sunscreens expose the skin to
chemicals that may cause other problems such as disruption of the skin barrier function or induction
of inflammation [56].
Vitamin-C-Mediated Protection against Photoaging and UV Damage
Changes to the skin due to UV exposure have much in common with the rather slower process of
‘natural’ aging, with one major difference being a more acute onset. It is established that vitamin C
limits the damage induced by UV exposure [
27
,
54
,
89
,
145
,
146
]. This type of injury is directly mediated
by a radical-generating process, and protection is primarily related to its antioxidant activity. This
has been demonstrated with cells
in vitro
and
in vivo
, using both topical and dietary intake of
vitamin C
[54,139,147,148]
. It appears that UV light depletes vitamin C content in the epidermis,
which also indicates that it is targeted by the oxidants induced by such exposure [
138
,
149
]. Vitamin
C prevents lipid peroxidation in cultured keratinocytes following UV exposure and also protects the
keratinocyte from apoptosis and increases cell survival [21,99,107].
Sunburn is measured as the minimal erythemal dose (MED) in response to acute UV exposure.
A number of studies have shown that supplementation with vitamin C increases the resistance
of the skin to UV exposure. However, vitamin C in isolation is only minimally effective, and
most studies showing a benefit use a multi-component intervention [
21
,
50
,
86
,
90
,
107
,
150
–
152
]. In
particular, a synergy exists between vitamin C and vitamin E, with the combination being particularly
effective [
50
]. These results indicate the need for complete oxidant scavenging and recycling as
indicated in Figure 4, in order to provide effective protection from UV irradiation. This combination
also decreases the inflammation induced by excessive UV exposure.
Topical application of vitamin C, in combination with vitamin E and other compounds, has also
been shown to reduce injury due to UV irradiation [
50
,
54
,
65
,
89
,
150
,
152
,
153
]. However, the efficacy of
topical vitamin C and other nutrients may depend on the pre-existing status of the skin. One study
suggests that when health status is already optimal there is no absorption of vitamin C following
topical application. Hence, “beauty from the inside”, via nutrition, may be more effective than topical
application [132].
Vitamin-C-mediated prevention of radiation injury from acute UV exposure is relatively easily
demonstrated, and these studies are highlighted above. However, reversal of photoaging due to
prior, chronic sun damage is much more problematic. Although there are a number of studies
that claim a significant benefit from an antioxidant supplement or topical cream, interpretation of
the data is confounded by the complex formulation of the interventions, with most studies using
a cocktail of compounds and with the formulation of topical creams providing a moisturising effect in
itself [23,61,88,154].
5.3. Dry Skin
Dry skin is a common condition typically experienced by most people at some stage in their lives.
It can occur in response to a particular skin care regime, illness, medications, or due to environmental
changes in temperature, air flow and humidity. The prevalence of dry skin also increases with age [
127
];
this was originally believed to be due to decreased water content or sebum production in the skin as
we get older. However, it is now considered likely to be due to alterations in the keratinisation process
and lipid content of the stratum corneum [127].

Nutrients 2017,9, 866 13 of 27
The pathogenesis of dry skin is becoming clearer and three contributing deficiencies have
been identified.
•
A deficiency in the skin barrier lipids, the ceramides, has been identified. These lipids are the main
intercellular lipids in the stratum corneum, accounting for 40 to 50 percent of total lipids [155].
•
A reduction in substances known as the natural moisturising factor (NMF) [
156
,
157
] is also
thought to be involved in dry skin. These substances are found in the stratum corneum within
the corneocytes, where they bind water, allowing the corneocyte to remain hydrated despite the
drying effects of the environment.
•
More recently, a deficiency of the skin’s own moisture network in the epidermis, mediated by the
newly discovered aquaporin water channels, has been suggested to play a role [131].
Treatment of dry skin involves maintenance of the lipid barrier and the natural moisturising factor
components of the stratum corneum, generally through topical application (91), although nutritional
support of the dermis may also be useful [135,156].
Potential for Vitamin C to Prevent Dry Skin Conditions
Cell culture studies have shown that the addition of vitamin C enhances the production of barrier
lipids and induces differentiation of keratinocytes, and from these observations it has been proposed
that vitamin C may be instrumental in the formation of the stratum corneum and may thereby influence
the ability of the skin to protect itself from water loss [
99
,
157
]. Some studies have indicated that topical
application of vitamin C may result in decreased roughness, although this may depend more on
the formulation of the cream than on the vitamin C content [
52
,
55
]. Because most studies in this
area involve topical application, the complex and variable effects (pH and additional compounds) of
topical formulations make it difficult to come to any firm conclusion as to whether vitamin C affects
skin dryness.
5.4. Wrinkles
Wrinkles are formed during chronological aging and the process is markedly accelerated by
external factors such as exposure to UV radiation or smoking. The formation of wrinkles is thought
to be due to changes in the lower, dermal layer of the skin [
22
] but little is known about the specific
molecular mechanisms responsible. It is thought that loss of collagen, deterioration of collagen and
elastic fibres and changes to the dermal–epidermal junction may contribute [
22
,
120
,
158
–
160
]. One
hypothesis is that UV light induces cytokine production, which triggers fibroblast elastase expression
causing degradation of elastic fibres, loss of elasticity and consequent wrinkle formation.
The Effect of Vitamin C on Wrinkle Formation and Reversal
The appearance of wrinkles, or fine lines in the skin, has a major impact on appearance and
is therefore often a focus of intervention studies. Most have used topical applications, generally
containing a mixture of vitamin C and other antioxidants or natural compounds, with varied
efficacy [
51
,
52
,
161
]. Generally the demonstration of wrinkle decrease in these studies is less than
convincing, and the technology to measure these changes is limited. More recently, improved and
impartial imaging technologies such as ultrasound have been used to determine the thickness of the
various skin layers [
135
,
149
]. Once again, the efficacy of topical vitamin C creams on wrinkled skin
may depend on the vitamin C status of the person involved. An indication that improved vitamin
C status could protect against wrinkle formation through improved collagen synthesis comes from
the measured differences in wound healing and collagen synthesis in smokers, abstinent smokers
and non-smokers with associated variances in plasma vitamin C status [
162
]. Smokers had depleted
vitamin C levels compared with non-smokers; these levels could be improved by smoking cessation,
with an associated improvement in wound healing and collagen formation [162].

Nutrients 2017,9, 866 14 of 27
5.5. Wound Healing
Wound healing is a complex process with three main consecutive and overlapping stages;
inflammation, new tissue formation and remodelling [
163
]. Following vasoconstriction and fibrin clot
formation to stem bleeding, inflammatory cells are recruited to the wound site. The first of these cells
is the neutrophil, which clears the wound of any damaged tissue and infectious material and signals
the recruitment of tissue macrophages [
164
]. Macrophages continue clearing damaged material and
bacteria, including spent neutrophils. Crucially, they are thought to be involved in orchestrating the
healing process, signalling fibroblasts to remodel tissue at the wound site and providing vital signals
for re-epithelialisation and dermal repair [163,164].
Re-epithelisation restores the skin’s barrier function, and occurs by a combination of migration
and proliferation of the epidermal keratinocytes that reside close to the damaged area. Epidermal stem
cells may also be involved in re-epithelisation [
163
]. In addition to the epidermal layer, the underlying
dermis must also be restored. Fibroblasts from a number of sources also proliferate and move into
the wound area [
165
], where they synthesise extracellular matrix components. These cells remove the
fibrin clot from the wound area, replacing it with a more stable collagen matrix. They are also involved
in wound contraction, and the reordering of collagen fibres. Proliferation of blood vessels is initiated
by growth factor production by macrophages, keratinocytes and fibroblasts.
Typically, the final result of the healing process is the formation of a scar. This is an area of
fibrous tissue generally made up of collagen arranged in unidirectional layers, rather than the normal
basket-weave pattern. As such, the strength of skin at the repair site is never as great as the uninjured
skin [
163
]. Variations in scar formation can occur, resulting in keloids—raised and fibrous scars—or
weak thin scar tissue. At this stage no intervention has been able to prevent the formation of scar tissue
although the extent of scarring may be ameliorated [
166
]. It is thought that nutritional support for
regeneration of the skin layers is important for development of strong healthy skin [167].
Vitamin C and the Benefits for Wound Healing
Of all effects of vitamin C on skin health, its beneficial effect on wound healing is the most
dramatic and reproducible. This is directly related to its co-factor activity for the synthesis of collagen,
with impaired wound healing an early indicator of hypovitaminosis C [
68
,
168
]. Vitamin C turnover at
wound sites, due to both local inflammation and the demands of increased collagen production, means
that supplementation is useful, and both topical application and increased nutrient intake have been
shown to be beneficial [
166
,
169
,
170
]. Supplementation with both vitamin C and vitamin E improved
the rate of wound healing in children with extensive burns [
171
], and plasma vitamin C levels in
smokers, abstaining smokers and non-smokers were positively associated with the rate of wound
healing [
162
]. However, it would appear that the extent of the benefits of supplemented vitamin C
intake is, once again, dependent upon the status of the individual at baseline, with any benefit being
less apparent if nutritional intake is already adequate [
167
,
168
]. However, the complexity and poor
selection of study population has often made it difficult to come to firm conclusions about the efficacy
of nutritional interventions, as summarised in a meta-analysis of the effects of varied treatments on
ulcer healing [
172
]. In a recent study, topical application of vitamin C in a silicone gel resulted in
a significant reduction in permanent scar formation in an Asian population [166].
5.6. Skin Inflammatory Conditions
Inflammation in the skin underlies a number of debilitating conditions such as atopic dermatitis,
psoriasis and acne, with symptoms including pain, dryness and itching. The pathology underlying
these conditions is complex and involves activation of auto-immune or allergic inflammation with
associated generation of cytokines and cellular dysfunction, and consequent breakdown of the
skin epidermal lipid barrier [
173
,
174
]. Treatments are therefore targeted at both the underlying
inflammation and the repair and maintenance of the epidermal structures. Nutrition plays an

Nutrients 2017,9, 866 15 of 27
integral part in both these aspects and numerous studies have investigated the impact of dietary
manipulation for alleviation of acute and chronic skin pathologies, although firm conclusions
as to efficacy remain elusive [
175
–
177
]. Treatments involving supplementation with essential
omega-fatty acids, lipid-soluble vitamins E and A are often employed in an attempt to assist the
generation of the lipid barriers and to retain moisture in the skin [
177
]. Vitamin C is often used in
anti-inflammatory formulations or as a component of nutrition studies but its individual efficacy has
not been investigated [175–177].
Vitamin C and Skin Inflammation
Vitamin C status has been reported to be compromised in individuals with skin inflammation,
with lower levels measured compared with unaffected individuals [
178
,
179
]. This may reflect increased
turnover of the redox-labile vitamin C, as is seen in many inflammatory conditions [
180
–
182
], and
decreased vitamin C status could be expected to impact on the numerous essential functions for which
it is essential as detailed in the sections above. Recent studies have begun to provide more detailed
information as to specific functional implications for suboptimal vitamin C status in inflamed skin
lesions. One notable study [
179
] has reported significantly compromised vitamin C status in patients
with atopic dermatitis, with plasma levels ranging between 6 and 31
µ
mol/L (optimal healthy levels
> 60
µ
M), and an inverse relationship between plasma vitamin C and total ceramide levels in the
epidermis of the affected individuals. As indicated in the sections above, ceramide is the main lipid of
the stratum corneum and its synthesis involves an essential hydroxylation step catalysed by ceramide
synthase, an enzyme with a co-factor requirement for vitamin C [
100
]. Hence the potential impact of
vitamin C extends far beyond its capacity as an inflammatory antioxidant in a pathological setting.
Table 3.
Skin ailments, their causes and evidence from
in vitro
and
in vivo
studies for association with
vitamin C levels.
Type of Skin
Damage Cause Skin Structure Affected Evidence of Protection
by Vitamin C References
Sunburn Acute and excessive
UV exposure.
Cell death of all skin cells,
with associated
inflammation.
Improving skin vitamin C and
vitamin E levels can improve
resistance to UV exposure.
[21,50,86,90,
107,150–152]
Photoaging,
oxidant-induced
damage
Chronic UV
overexposure,
cigarette smoking.
Damaged collagen and
elastin matrix, thinning of
the epidermal layer.
Decreased signs of aging with
higher fruit and vegetable
intake. Protection inferred
from studies with acute UV
exposure.
[27,54,89,139,
145–148]
Hyperpigmentation
Chronic UV exposure
and environmental
stresses.
Excessive pigment
formation and propagation
of melanocytes in the
epidermis.
Nutrition studies showing
improved skin colour with
higher fruit and vegetable
intake.
Reviewed in
[134,135]
Wrinkle formation
Natural aging,
oxidative stress, UV
exposure, smoking,
medical treatments.
Dermal layer changes,
deterioration of collagen and
elastic fibres.
Lessening of wrinkle depth
following vitamin C
supplementation. Increased
collagen formation by
fibroblasts in cell culture.
[69,73,79–82,
135,149]
Skin sagging
Natural aging,
oxidative stress
damage, extreme
weight loss.
Loss of elastin and collagen
fibres, thinning of skin
layers, loss of muscle tone.
Improved skin tightness in
individuals with higher fruit
and vegetable intake.
Reviewed in
[134,135]
Loss of colour Natural aging, UV
exposure, illness.
Thinning of skin layers, loss
of melanocytes or decreased
melanin formation, loss of
vasculature in dermis.
Improved skin tone with high
fruit and vegetable intake.
Reviewed in
[94,95,134,135]
Surface roughness
Chemical and UV
exposure, physical
abrasion, allergy and
inflammation.
Stratum corneum, loss of
skin moisture barrier
function.
Vitamin C enhances
production of barrier lipids in
cell culture.
[98–102,157]

Nutrients 2017,9, 866 16 of 27
Table 3. Cont.
Type of Skin
Damage Cause Skin Structure Affected Evidence of Protection
by Vitamin C References
Dry skin
Medications, illness,
extreme temperature,
low humidity and
wind exposure.
Stratum corneum, loss of
skin barrier lipids and
natural moisturising factor.
Vitamin C enhances
production of barrier lipids in
cell culture.
[98–102,157]
Excessive scar
formation,
generation of keloids
Ineffective wound
healing.
Fibroblast function, collagen
and elastin formation.
Supplementation improves
wound healing, prevents
keloid formation in vivo,
enhances collagen formation
by fibroblasts in vitro.
[73,79–82,166,
167]
Poor wound healing,
thickening rough
skin
Vitamin C deficiency.
All skin cell functions,
collagen formation.
Direct association Vitamin C
deficiency prevents wound
healing.
[162,166,169]
Inflammatory skin
lesions
Allergic and
auto-inflammation.
Skin barrier integrity,
underlying inflammation
and swelling.
Nutrition support, decreased
levels associated with loss of
barrier lipid ceramide.
[179]
Table 4.
Summary of key and recent
in vivo
studies providing evidence of vitamin C effects in the skin.
Study Description Measured Parameters Outcome and Comment References
Animal Studies
Oral Supplementation
Dietary supplementation of
pregnant female rats. Addition of
1.25 mg/mL vitamin C to drinking
water for duration of gestation.
Monitored collagen and elastin
content of uterosacral ligaments
by histology staining and
subjective assessment.
Increased collagen production in vit.-
C-supplemented rats, decreased elastin
loss. Implied prevention of pelvic organ
prolapse and stress urinary incontinence.
[183]
Wound healing in guinea pigs
following supplementation with
moderate and high-dose vit. C.
Dorsal wound healing rate and
strength of repair monitored.
Increased vit. C associated with faster
wound recovery and strength of skin
integrity. Small sample size limited stats.
[184]
Topical application
Topical application of vit. C and
vit. E-containing cream to nude
mice, followed by UV irradiation.
Measured melanocyte
differentiation post-irradiation.
Change of skin colour—tanning,
inflammation.
UVR-induced proliferation and
melanogenesis of melanocytes were
reduced by vit. C and E. Melanocyte
population and confluence reduced
when vit. C present.
[185]
Cultured skin—human
keratinocytes and fibroblasts
attached to
collagen-glycosamino-glycan
substrates, incubated for five
weeks ±0.1 mM vit. C, and then
grafted to athymic mice.
Collagen IV, collagen VII and
laminin 5 synthesis, epidermal
barrier formation and skin graft
take in athymic nude mice.
Increased cell viability and basement
membrane development in vitro, better
graft ability in vivo.
[157]
Human Studies
Oral supplementation
90-day oral supplementation with
a fermented papaya preparation
or an antioxidant cocktail (10 mg
trans-resveratrol, 60 µg selenium,
10 mg vitamin E, 50 mg vitamin C)
in 60 healthy non-smoker males
and females aged 40–65 years, all
with clinical signs of skin aging.
Skin surface, brown spots, skin
evenness, skin moisture,
elasticity (face), lipid
peroxidation, superoxide
dismutase levels, nitric oxide
(NO) generation, and the
expression levels of key genes
(outer forearm sample).
Improved skin elasticity, moisture and
antioxidant capacity with both
fermented papaya and antioxidant
cocktail. Increased effect of papaya
extract and on gene expression. No
baseline measures in study population.
Antioxidant components of the
fermented papaya unknown and direct
link with vit. C not available.
[135]
Intervention with 47 men aged
30–45 given oral supplement of 54
mg or 22 mg of vit. C, 28 mg
tomato extract, 27 mg grape seed
extract, 210 mg of marine complex,
4 mg zinc gluconate for 180 days.
Subjective assessment of
appearance and objective
measures of collagen and elastin
(histology and measurement in
biopsy material).
Improvement in erythema, hydration,
radiance, and overall appearance.
Decreased intensity of general skin spots,
UV spots, and brown spots, improved
skin texture and appearance of pores.
Increased collagen (43%–57%) and
elastin (20%–31%).
[49]

Nutrients 2017,9, 866 17 of 27
Table 4. Cont.
Study Description Measured Parameters Outcome and Comment References
Supplementation of 33 healthy
men and women (aged 22–50),
with placebo, 100 mg vit. C or 180
mg vit. C daily for four weeks.
EPR measurement of TEMPO
scavenging in skin on arm.
Raman resonance spectroscopy
for skin carotenoids.
Improved oxygen radical scavenging
with vit. C supplementation, dose
dependency indicated and rapid
response (obvious within two weeks).
[38]
Three month supplementation of
12 males and six females (21–77 y)
with 2 g vit. C and 1000 IU
D-alpha-tocopherol.
Measured blood vitamin levels
before and after, skin resilience
to UVB, detection of DNA
crosslinks in skin biopsy.
Serum vit. C and vit. E doubled during
intervention (implies sub-saturation at
baseline). Minimal erythema dose
increased with supplementation, DNA
damage halved.
[20]
Investigation of antioxidant
capacity in human skin before and
after UV irradiation; effect of
supplementation with 500 mg vit.
C per day.
Measurement of erythema and
antioxidant levels following
UVB irradiation.
Vit. C and E levels increased, but levels
not realistic (plasma vit. C 21 µM before
and 26 µM after 500 mg daily). Skin
MDA and glutathione content lowered,
no effect on MED.
[27]
Topical application
Topical application of vit. C cream
in advance of application of hair
dye product p-phenylenediamine.
Visual assessment of allergic
reaction following patch
application on volunteer skin
(on back).
Decreased or ablation of dermatitis and
allergic response due to local antioxidant
action of vit. C in cream.
[170]
Clinical study applying vit. C in
liposomes to human skin
(abdomen), then exposure to UV
irradiation.
Measured penetration through
skin layers, delivery of vit. C,
loss of Trolox, TNFalpha and
Il-1beta.
Increased vit. C levels in epidermis and
dermis with liposomes. Protection
against UV increased over liposomes
alone.
[67]
Microneedle skin patches to
deliver vit. C into the skin
assessed on areas of slight wrinkle
formation (around eyes).
Global Photodamage Score by
visual inspection. Skin replica
analysis and skin assessment by
visiometer.
Slightly improved photodamage score
and lessening of wrinkles after 12 weeks
of treatment with vit. C-loaded patches.
[186]
Vit. C-based solution containing
Rosa moschata oil rich in vitamins
A, C, E, essential fatty acids
/placebo moisturizer cream
applied to facial skin of 60 healthy
female subjects for 40–60 days.
Ultrasound monitoring
thickness of the epidermis and
dermis, and low (LEP), medium
(MEP), high echogenic pixels
(HEP), reflecting hydration,
inflammatory processes, elastin
and collagen degeneration
(LEP), and structure of collagen,
elastin and microfibrils (MEP
and LEP).
Data suggest epidermis but not the
dermis increased in thickness. Increase
in MEP and HEP (collagen and elastin
synthesis) and decreased LEP
(inflammation and collagen
degeneration). No vit. C status
measurements in skin of individuals.
[149]
In vivo study with 30 healthy
adults. Protective effect of SPF30
sunscreen with and without
anti-oxidants (vit. E, grape seed
extract, ubiquinone and vit. C)
against Infra-Red A irradiation on
previously unexposed skin
(buttock).
Skin biopsy analysis; mRNA
and RT-PCR for matrix
metalloprotein-1 (MMP-1)
expression 24 h post irradiation.
Sunscreen plus antioxidants protected
skin against MMP-1 increase, sunscreen
alone did not. No indication of levels of
antioxidants, or whether they were able
to penetrate into skin layers.
Multi-component antioxidant mix.
[153]
In vivo study of 15 healthy adults.
Protective effect of vitamin C
mixtures (vit. C, vit. E, ferulic acid
OR vitamin C, phoretin, ferulic
acid) on ozone exposure on
forearms.
Skin biopsy analysis; 4-HNE
and 8-iso prostaglandin levels,
immunofluorescence for NF-kB
p65, cyclooxygenase-2, matrix
metalloprotein-9 (MMP-9), type
III collagen. After 5 days of 0.8
ppm ozone for 3h/d.
Vitamin C mixture reduced ozone
induced elevation in lipid peroxidation
products, NF-kB p65, cyclooxygenase-2
expression and completely prevented
MMP-9 induction by ozone. No
indication of levels of antioxidants, or
whether they were able to penetrate into
skin layers. Multi-component
antioxidant mix.
[187]
Test of topical silicone gel with vit.
C on scar formation in a
population of 80 Asian people.
Gel applied for six months after
operation.
Scar formation monitored by
modified Vancouver Scar Scale
(VSS) as well as erythema and
melanin indices by
spectrophotometer.
Vit. C decreased scar elevation and
erythema, decreased melanin index.
Improved wound healing (stitch
removal).
[166]
6. Conclusions
The role of vitamin C in skin health has been under discussion since its discovery in the 1930s as
the remedy for scurvy. The co-factor role for collagen hydroxylases was the first vitamin C function

Nutrients 2017,9, 866 18 of 27
that was closely tied to the symptoms of scurvy and the realisation of the importance of this function
for the maintenance of skin health throughout the human lifespan led to the hypothesised skin health
benefit of vitamin C. In addition, the antioxidant activity of vitamin C made it an excellent candidate
as a protective factor against UV irradiation. These two hypotheses have driven most of the research
into the role of vitamin C and skin health to date.
The following information is available as a result of research into the role of vitamin C in skin
health, and Tables 2and 4list a sample of key studies:
•
Skin fibroblasts have an absolute dependence on vitamin C for the synthesis of collagen, and for
the regulation of the collagen/elastin balance in the dermis. There is ample
in vitro
data with
cultured cells demonstrating this dependency. In addition, vitamin C supplementation of animals
has shown improved collagen synthesis in vivo.
•
Skin keratinocytes have the capacity to accumulate high concentrations of vitamin C, and this
in association with vitamin E affords protection against UV irradiation. This information is
available from
in vitro
studies with cultured cells, with supportive information from animal and
human studies.
•
Analysis of keratinocytes in culture has shown that vitamin C influences gene expression of
antioxidant enzymes, the organisation and accumulation of phospholipids, and promotes the
formation of the stratum corneum and the differentiation of the epithelium in general.
•
Delivery of vitamin C into the skin via topical application remains challenging. Although some
human studies have suggested a beneficial effect with respect to UV irradiation protection, most
effective formulations contain both vitamins C and E, plus a delivery vehicle.
•
Good skin health is positively associated with fruit and vegetable intake in a number of
well-executed intervention studies. The active component in the fruit and vegetables responsible
for the observed benefit is unidentified, and the effect is likely to be multi-factorial, although
vitamin C status is closely aligned with fruit and vegetable intake.
•
Signs of aging in human skin can be ameliorated through the provision of vitamin C. A number
of studies support this, although measurement of skin changes is difficult. Some studies include
objective measures of collagen deposition and wrinkle depth.
•
The provision of vitamin C to the skin greatly assists wound healing and minimises raised scar
formation. This has been demonstrated in numerous clinical studies in humans and animals.
Acknowledgments:
The writing of this review was funded by the University of Otago and Zespri International.
No additional costs were obtained to publish in open access. Anitra Carr is the recipient of a Health Research
Council of New Zealand Sir Charles Hercus Health Research Fellowship.
Author Contributions:
Juliet Pullar and Margreet Vissers wrote the bulk of the review, with additional input and
editing from Anitra Carr.
Conflicts of Interest:
The authors declare no conflict of interest. Zespri International, a partial funder, had no
influence on the selection of material to cover, nor on the focus and interpretation of the studies reviewed.
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