Recent Trends of Sunscreen Cosmetic: An Update Review

Abstract

Ultraviolet (UV) radiation has been demonstrated to cause skin disorders, including sunburn and relative symptoms of prolonged exposure. It has been reported that sunscreens have beneficial effects in reducing the incidence of skin disorders (sunburn, skin aging, and immunosuppression) through their ability to absorb, reflect, and scatter UV. Many commercial products have recently been manufactured from not only usual organic and inorganic UV filters, but also hybrid and botanical ingredients using typical formulations (emulsion, gel, aerosol, and stick). Particularly, these products have been supplemented with several preeminent properties to protect against the negative effects of not only UVB, but also UVA. However, the use of sunscreen has faced many challenges, including inducing photoallergic dermatitis, environment pollution, and deficiency of vitamin D production. Therefore, consumers should efficiently apply suitable products to improve sun protection. as well as to avoid the side effects of sunscreen.

Full text

Cosmetics 2019, 6, 64; doi:10.3390/cosmetics6040064 www.mdpi.com/journal/cosmetics
Review
Recent Trends of Sunscreen Cosmetic:
An Update Review
Le Thi Nhu Ngoc
1
, Vinh Van Tran
1
, Ju-Young Moon
2
, Minhe Chae
3
, Duckshin Park
4,
*
and Young-Chul Lee
1,
*
1
Department of BioNano Technology, Gachon University, 1342 Seongnam-Daero, Sujeong-Gu, Seongnam-
Si, Gyeonggi-do 13120, Korea; nhungocle92@gmail.com (L.T.N.N.); vanvinhkhmtk30@gmail.com (V.V.T.)
2
Department of Beauty Design Management, Hansung University, 116 Samseongyoro-16gil, Seoul 02876,
Korea; bora7033@naver.com
3
Biocell Korea Co., Ltd., 1-2F Janghan B/D,54 Bongeunsa-ro 30-gil, Gangnam-gu, Seoul 04631, Korea;
christinechae7@gmail.com
4
Korea Railroad Research Institute (KRRI), 176 Cheoldobakmulkwan-ro,
Uiwang-si 16105, Gyeonggi-do, Korea
* Correspondence: dspark@krri.re.kr (D.P.); dreamdbs@gachon.ac.kr (Y.-C.L.);
Tel.: +82-10-3343-2862 (D.P.); +82-31-750-8751 (Y.-C.L.);
Fax: +82-31-460-5367 (D.P.); +82-31-750-4748 (Y.-C.L.)
Received: 1 October 2019; Accepted: 29 October 2019; Published: 1 November 2019
Abstract: Ultraviolet (UV) radiation has been demonstrated to cause skin disorders, including
sunburn and relative symptoms of prolonged exposure. It has been reported that sunscreens have
beneficial effects in reducing the incidence of skin disorders (sunburn, skin aging, and
immunosuppression) through their ability to absorb, reflect, and scatter UV. Many commercial
products have recently been manufactured from not only usual organic and inorganic UV filters,
but also hybrid and botanical ingredients using typical formulations (emulsion, gel, aerosol, and
stick). Particularly, these products have been supplemented with several preeminent properties to
protect against the negative effects of not only UVB, but also UVA. However, the use of sunscreen
has faced many challenges, including inducing photoallergic dermatitis, environment pollution,
and deficiency of vitamin D production. Therefore, consumers should efficiently apply suitable
products to improve sun protection. as well as to avoid the side effects of sunscreen.
Keywords: sunscreen; organic/inorganic/hybrid/botanical agents; emulsion/gel/aerosol/stick
formulations; antioxidants/anti-pollutants/defense-blue light and -IR
1. Introduction
Solar radiation reaching the terrestrial surface comprises ultraviolet (UV), visible light, and
infrared (IR) rays [1]. The spectra of all electromagnetic radiation range from 100 nm to 1 mm, in
which UV radiation has the shortest wavelength (200–400 nm) compared to visible light (400–740
nm) and IR (760–1,000,000 nm). UV radiation constitutes about 10% of the total light output of the
sun [2]. The broad spectrum of UV radiation is subdivided into three recommended ranges (UVA,
UVB, and UVC). Therein, UVA has the longest wavelength (320–400 nm) but the least energy
photon, while UVB wavelength is in the middle span (280–320 nm) and UVC has the shortest
wavelength (100–280 nm) but the highest energy [2]. It has been reported that moderate sun
exposure offers a number of beneficial effects, including production vitamin D [3], antimicrobial
activity [4], and improved cardiovascular health [5,6]. However, long-term exposure to UV rays is
considered to be a potential risk of skin cancer and acute and chronic eye injuries (Figure 1) [7].

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Figure 1. Electromagnetic spectra solar ultraviolet (UV) rays and their biologic effects on the skin [2].
UV-induced skin damage is one of the most common concerns in the world. Certainly, UVA is
a risk of skin aging, dryness, dermatological photosensitivity, and skin cancer. It damages DNA
through the generation of reactive oxygen species (ROS), which causes oxidative DNA base
modifications and DNA strand breaks, resulting in mutation formation in mammalian cells [1,2,8].
On the other hand, UVB can directly damage DNA through the formation of pyrimidine dimer and
then cause apoptosis or DNA replication errors, leading to mutation and cancer [5]. Although UVC
is the shortest and most energetic wavelength, it is the most dangerous type of UV ray because it
can cause various adverse effects (e.g., mutagenic and carcinogenic) [5]. However, UVC rays do not
penetrate through the atmosphere layer.
It has been proved that photoprotectors, especially sunscreen, play a critical role in reducing
the incidence of human skin disorders (pigment symptoms and skin aging) induced by UV rays [9].
Sunscreen was first commercialized in the United States in 1928 and has been expanded worldwide
as an integral part of the photoprotection strategy [9]. It has been found to prevent and minimize
the negative effects of UV light based on its ability to absorb, reflect, and scatter solar rays [10,11].
Over the decades of development, sunscreens have been improved step-by-step, accompanying the
innovation of photoprotective agents [12]. Certainly, recent sunscreens are found to not only
address UV effects, but also protect the skin from other risks (e.g., IR, blue light, and pollution)
[13,14]. Indeed, while UV radiation is most commonly implicated in skin disorder development, it
is crucial to note the potential role of these considerable harmful factors [13,15]. It has been
suggested that these factors can worsen disorders of dyspigmentation, accelerating aging, and
eliciting genetic mutations [15,16].
Furthermore, the photoprotective efficiency of sunscreen is determined through sun protection
factor (SPF) and the protection grade of UVA (PA) values. According to Food and Drug
Administration (FDA) regulations, commercial products must be labeled with SPF values that
indicate how long they will protect the user from UV radiation and must show the effectiveness of
protection [17]. Certainly, the SPF values are generally in the range of 6–10, 15–25, 30–50, and 50+,
corresponding to low, medium, high, and very high protection, respectively [17]. Nevertheless,
there are some fundamental misunderstandings of the SPF. Some argument is that an SPF 15
sunscreen can absorb 93% of the erythemogenic UV radiations, while an SPF 30 product can block

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96%, which is just over 3% more (Figure 2) [18]. The argument may be correct when evaluating sun
protection capacity, but is not sufficient in assessing the amount of UV radiation entering the skin.
In other words, half as much UV radiation will penetrate into the skin when applying an SPF 30
product compared to an SPF 15 product. [18]. This is also illustrated by comparing SPF 10 with SPF
50 sunscreen. Ten and two photons transmit (%) through sunscreen film and enter the skin when
applying SPF 10 and SPF 50 products, respectively, as a difference factor of five it is expected [18].
On the other hand, in 1996, the Japan Cosmetic Industry Association (JCIA) developed an in vivo
persistent pigment darkening (PPD) method to evaluate UVA efficacy of sunscreen [19]. Sunscreens
are labeled with PA+, PA++, PA+++, and PA++++, corresponding to the level of protection grade of
UVA (PA) obtained from the PPD test [19,20]. Sunscreens labeled as PA+ express low protection,
mainly contributed by between two and four UVA filters. Sunscreens containing four to eight
sunscreen agents show moderate levels of UVA blocking and are labeled as PA++. In contrast, the
PA+++ and PA++++ symbols represent products that are composed of more than eight UVA filters
and provide a high sunscreen efficacy [10,19,20].
Figure 2. Illustration of the sun protection factor (SPF) definitions, including filtered and
transmitted UV radiation [18].
In the literature, there are several published studies that fully introduce the basics of sunscreen
products, such as ingredients, properties, and SPF evaluation, while formulas and novel properties
(anti-pollutant, antioxidant, and blocking blue light and IR) have not clearly described. In order to
provide a comprehensive summary of modern sun protection, this review specially focused on
describing the ingredients and formulations of commercial products. In addition, it refers to the
novel properties of sunscreen that can satisfy consumer demands, such as antioxidant, DNA repair
enzymes, anti-pollutant, and defense-blue light and -IR.
2. Classification of Sunscreen Agents
Sunscreen agents are basically categorized into inorganic and organic UV filters which have
specific mechanisms of action upon exposure to sunlight (Figure 3). Inorganic agents reflect and
scatter light, while organic blockers absorb high-energy UV radiation [21,22]. Recently, hybrid
materials combining properties of organic and inorganic compounds have attracted the attention of
scientists as a promising sunscreen agent. Remarkably, botanical agents, which contain large

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amounts of antioxidant compounds, can be used as inactive ingredients to protect the skin against
adverse effects (e.g., photoaging, wrinkles, and pigment).
Figure 3. Sunscreen agent classification [23].
2.1. Organic UV Filters
Organic blockers are classified into either UVA (anthranilates, dibenzoylmethanes, and
benzophenones) or UVB filters (salicylates, cinnamates, para-aminobenzoic acid (PABA)derivatives,
and camphor derivative), which play an important role in absorption activity of sunscreen (Figure
3) [24]. These agents show outstanding safety and aesthetic properties, including stability,
nonirritant, nonvolatile, non-photosensitizing, and non-staining to human skin, compared to
inorganic UV filters [25]. Besides, they are mostly used in combination at levels currently allowed
by the FDA to provide broad-spectrum absorption, as well as increased SPF values [26].
Nevertheless, the combination is limited in selecting the appropriate UVA/UVB filters to avoid
possible negative interactions between the combining agents [25]. Particularly, some organic filters
(e.g., PABA, PABA derivatives, and benzophenones) show considerable negative effects, including
eczematous dermatitis, burning sensation, and increased risk of skin cancer [24]. Therefore,
sunscreens have recently minimized or avoided the use of these compounds to protect consumers
from undesirable effects. For example, the use of the two most popular organic filters, octinoxate
(ethylhexul methoxycinnamate) and oxybenzone, has recently been restricted in Hawaii because of
their negative effect on the coral reefs [27]. Besides, some photo unstable filters (e.g., avobenzone
and dibenzoylmethanes) show a number of photoreactive results in the formation of photoproducts
that can absorb in different UV regions, therefore reducing their photoprotective efficacy [28–30].
Particularly, these photodegradation products can come in direct contact with the skin, thus
promoting phototoxic, photosensitizing, and photoallergic contact dermatitis on the skin [30].
2.2. Inorganic UV Filters
Inorganic blockers have been approved to protect human skin from direct contact with
sunlight by reflecting or scattering UV radiation over a broad spectra [9]. The current agents are
ZnO, TiO2, FexOy, calamine, ichthammol, talc, and red veterinary petrolatum (Figure 3) [11].
Although they are generally less toxic, more stable, and safer for human than those of organic
ingredients, they are visible due to white pigment residues left on the skin and can stain clothes
[11]. Since the early 1990s, these metal oxides have been synthesized in the form of micro and

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nanoscale particles (10–50 nm), which can reduce the reflection of visible light and make them
appear transparent throughout the skin, resulting in enhance aesthetics over the larger size [11]. For
instance, micro-size TiO2 and ZnO have been replaced nano-size TiO2 and ZnO in sunscreen,
eliminating undesired opaqueness and improve SPF value [31].
Moreover, the main disadvantage of utilization of nanoparticles (NPs) is that sunscreens tend
to block shorter wavelength from UVAII to UVB rather than long radiation (visible and UVA
range). In particular, most NPs can produce ROS radicals and are small enough to penetrate into
the stratum corneum, thus causing severe skin effects with prolonged exposure, such as
photoallergic contact dermatitis and skin aging [32]. Therefore, in order to improve natural
appearance as well as reduce side effects on the skin, these cosmetics using nanoparticles need to be
controlled by numerous factors, including particles size and distribution, agglomeration and
aggregation, and morphology and structure of the NPs [28]. For examples, the utilization of TiO2
and ZnO NP-coated silicon or doped elements (Al2O3 and Zr) can minimize ROS production and
prevent negative effects as mentioned above [11,33].
2.3. Hybrid UV Filters (Organic/Inorganic Agents)
According to the literature, hybrid materials are two half-blended materials intended to create
desirable functionalities and properties [13]. They are constituted of organic components (molecule
or organic polymer) mixed with inorganic components (meal oxides, carbonates, phosphates,
chalcogenides, and allied derivatives) at the molecular or nanoscale [34]. The combination creates
ideal materials with a large spectrum and high chemical, electrochemical, optical transparency,
magnetic, and electronic properties [13]. Furthermore, some less toxic and biocompatible hybrid
materials have been utilized as active ingredients in cosmetics due to their ability to absorb or
deliver organic substances into the hair cuticle and skin layers, thereby improving skin care effect
[34]. For instance, L’Oréal and Kerastase have introduced the Intra-CylaneTM shampoo, which
contains amino functionalized organosilanes hybrid substances that not only protect against hair
damage, but also create hair volume expansion, better mechanical properties, and better texture
[34]. Merch KgaA and EMD Chemicals Inc. have utilized a number of hybrid compounds, such as
silica microcapsules, to control the release of active ingredients that can reduce skin aging and
provide high SPF [34].
2.4. Botanical Agents
Botanical agents are secondary metabolites produced by living organisms which play a crucial
role in the growth and continuity of these organisms [35]. It has been indicated that metabolites
possess antioxidant and UV ray absorption abilities [35]. Their featured properties are related to 𝜋-
electron systems, which are mainly found in conjugated bond structures expressed in linear chain
molecules and in most of aromatic compounds containing electron resonances [35]. Certainly, there
is no denying that UV radiation can generate huge amounts of ROS radicals, which leads to
inflammation, neutrophil infiltrate activates nicotinamide adenine dinucleotide phosphate
(NADPH) oxidase, and sebaceous gland dysfunction, and accelerates skin pigmentation and dermal
matrix [36,37]. In the presence of antioxidants, the ROS radicals are directly scavenged and
prevented from their biological targets. As a consequence, the propagation of oxidants is limited,
resulting in preventing aging [38].
These antioxidant compounds are obtained from vitamin C, vitamin E, and plant extracts
(phenolic, carotenoids, and flavonoid compounds) (Figure 3 and Table 1) [39]. In fact, a large
number of botanicals have been approved as inactive agents for preserving, emulsifying,
moisturizing, and smoothing sunscreen to further protect the skin. These typical varieties are Aloe
vera, tomatoes, pomegranate, green tea, cucumber, Pongamia pinnata (L.)-Indian beech tree,
Spathodea campanulata (L.)-African tulip tree, Dendropanax morbifera, and Opuntia humifusa [39–47].

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Table 1. Photoprotection mechanism of antioxidant compounds.
Compounds Protection Mechanism
Vitamin C
− Neutralizing ROS radicals in aqueous compartments of the skin based on
the oxidation capacity of ascorbate [37,48]
− Reducing sunburn cell formation, erythema, and immunosuppression [48]
− Inhibiting tyrosinase synthesis and maintaining hydration to protect the
skin epidermis barrier [37,48]
− Challenging: poor skin penetration and instability [48]
Vitamin E
− Protecting the cell membrane from oxidative stress [48]
− Inhibiting UV-induced cellular damage: photoaging, lipid peroxidation,
immunosuppression, and photocarcinogenesis [48,49]
Phenolic
compounds
− Scavenging free radicals [48]
− Conserving proper skin structure through the regulation of matrix
metalloproteinases (MMPs) [50]
− Inhibiting collagenase and elastase thus facilitating the maintenance of
proper skin structure [51].
Flavonoid
compounds
− Their double bonds in flavonoid molecules provide a high ability to absorb
UV [51]
− The presence of hydroxyl groups attached to aromatic rings also
contributes to their ROS scavenging capacity [51]
Carotenoids
− Physical quenching function: efficacy antioxidants for scavenging peroxide
and singlet molecular oxygen (1O2) radicals generated in during
photooxidation [52]
− Absorbing of UV, visible, and blue light [52]
2.5. Safety and Health Hazards of Sunscreen Agents
According to the literature, sunscreen agents should be safe, nontoxic, chemically inert, non-
irritating, and fully protect against broad spectrum that can prevent photocarcinogenesis and
photoaging [53]. However, they also have negative effects, including contact sensitivity,
estrogenicity, photoallergic dermatitis, and risk of vitamin D deficiency [54,55].
It has been reported that an increased incidence of melanoma may result from the use of
sunscreen. Gorham et al. (2007) pointed out that some commercial sunscreens completely absorb
UVB, but transmit large amounts of UVA, which may contribute to risk of melanoma in
populations at latitudes greater than 40 ℃ [56]. In addition, intentional long-term topical sunscreen
can increase melanoma risk, especially when using high-SPF products. Thus, the labeling of
sunscreen should inform consumers about the carcinogenic hazards related to sunscreen abuse [57].
Moreover, some sensitive ingredients in sunscreen may also be a photoallergic factor. In
particular, PABA and oxybenzone are the most common ingredients causing skin disorders [9]. The
penetration and systemic toxic effects of inorganic agents at micro- or nano-size have been reported
through several in vivo and in vitro analyses. Pan et al. (2009) demonstrated that TiO2 NPs (15 ± 3.5
nm) can pass through cell membranes and impair the function of human dermal fibroblast cultures
[58]. Filipe et al. (2006) suggested that TiO2 NPs (~20 nm) in sunscreen appear on the skin surface
and in the stratum corneum regions. Therefore, it does not penetrate deeply into the skin [59].
On the other hand, although UVB can cause sunburn for long-term exposure, it is responsible
for more than 90% of individual vitamin D production on skin [60]. There are controversies about
vitamin D deficiency due to sunscreen application. In particular, this photoprotection can lead to a
significant reduction in the amount of pre-vitamin D3 produced by sunlight in the skin, resulting in
insufficient vitamin D levels [60]. In contrast, Fourschou et al. (2012) indicated that vitamin D
synthesis increases exponentially with the application of thinner layers of sunscreen (<2 mg/cm2)
[55]. On the other hand, Marks et al. (1995) reported adequate production of vitamin D in the

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Australian population during the summer in most people using sunscreen or without these skin
protection substances [61].
3. Sunscreen Formulations
3.1. Emulsion Sunscreen
An emulsion is termed a lotion or cream depending on its viscosity, respectively, below 50,000
and in the range of 150,000–500,000 centipoises, providing almost unlimited versatility [62]. It is
normally produced from two unmixable liquid phases (oil and water), namely “water-in-oil (W/O)”
and “oil-in-water (O/W)” emulsions [63]. Moreover, multiple emulsions (O/W/O and W/O/W),
containing both O/W and W/O phases in a stable system, show an effective application in recent
sun protection technology [64]. Therein, water accounts for the largest proportion, while active
ingredients contribute a little amount in an emulsion product. Thus, emulsion sunscreens are cost-
effective vehicles [62]. These formulations possess the ability to spread more easily on the skin and
disperse from bottles [63]. Further, this formula shows great effectiveness in strategies to achieve
high SPF, create a uniform, thick and nontransparent sunscreen film when applied on the skin, and
minimize undesirable interaction among active sunscreen ingredients [62,63]. In other words,
emulsion sunscreens also provide an elegant medium that can give the skin a smooth and silky
feeling without greasy shine [63]. However, these are extremely difficult to stabilize, especially at
high temperatures [62].
3.2. Gel Sunscreen
Sunscreen gel seems to represent an ideal vehicle from an aesthetic perspective due to its
purity and elegance. It is categorized into four main forms, namely aqueous, hydroalcoholic,
microemulsion, and oil anhydrous formulations [62].
The aqueous gel must be composed of water and solubilizers (e.g., nonionic surfactants,
organic agents, and phosphate esters) at sufficient proportions to ensure the gel will be transparent
at all temperatures. Therefore, it is easily washed away when exposed to water or sweat [62,65].
Although organic active molecules (e.g., octyldimethyl PABA or octyl p-methoxycinnamate) are
primarily attributed to the formula, they are used in low doses due to their high levels of
carcinogenicity [65]. Interestingly, the high concentration of organic filters is primarily responsible
for increasing the SPF value. Thus , the aqueous gel provides low SPF compared to other kinds of
gel sunscreens [65].
The hydroalcoholic gels are formulated by alcohol (ethanol) in conjunction with water, which
are important in reducing additional solutes because most lipophilic ingredients are readily
miscible in alcohol [66]. This form can provide the desired cooling effect, which is especially
refreshing when applied to the skin on summer days [62]. However, this formulation also shows
some negative aspects, such as quickly being washed way in the water, causing facial or eye sting
on certain individuals, and providing low SPF [62,66].
The microemulsion gels are composed of small particles, allowing them to appear smooth,
thick, and evenly on the skin, thus delivering an elegant feel and high SPF [62,67]. Unfortunately, it
is markedly expensive to achieve transparent microemulsions containing high-level emulsifiers (15–
25%) [62]. Particularly, most emulsifiers are irritating components, so this emulsion system pose a
risk to human health [62]. In addition, high emulsification proportion results in reduced water-
resistance of these sunscreen products.
The oil anhydrous formula possesses many attributes similar to ointments. However, oil
anhydrous products are clear, while the ointments are translucent [62,66]. These products can be
produced as a gel by combining mineral oil and special silica [62,68]. However, they are not widely
sold because they are difficult to produce and quite expensive.

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3.3. Aerosol Sunscreen
In addition to lotions and creams, aerosol sunscreens are topically applied to protect skin
disorders from harmful sunlight. These products can be easily spread onto the surface of skin, and
distribute active ingredients to form a thin film on the skin [69]. However, this application may
result in the uneven spreading of sunscreen agents, corresponding to some high-coverage areas
with an excessive amount of sunscreen and other areas with little coverage to protect the skin
satisfactorily [69]. Nevertheless, the aerosol products have not become as popular as other
sunscreens due to some critical negative aspects. First, they are typically oil-based, making them
quite expensive and often reducing their effectiveness [62]. In addition, it is hard observe where the
sunscreen has been applied. Caution must be taken to avoid accidentally spraying sunscreen into
the eyes [62].
3.4. Sun Stick
The sun stick is undoubtedly one of the most convenient products due to its small size and
light weight. The sun stick is produced by two main emulsion components, namely oil and oil-
soluble components, through the incorporation of petrolatum and waxes. Thus, it tends to have a
greasy feel on the skin, which is a common problem of most water-resistant sunscreens [62].
However, this product has gained great attention due to its ability to cover a very small surface area
during each application. It is also easy to carry and re-touch [14]. This form is subdivided into three
categories, namely transparent, semi-transparent, and matte sunscreen [14]. The transparent
formula contains only chemical UV filters, while semi-transparent is formulated mainly by
chemical and mineral substances and matte is composed of only mineral sunscreen ingredients [14].
4. Novel Properties of Commercial Sun Protection Products
4.1. Sunscreen with Antioxidants and Anti-Aging
Regarding the beneficial effects of natural agents, many sunscreens have been produced by
combining one or more natural ingredients (e.g., extracts and nutrient compositions) and
conventional ingredients (e.g., TiO2, ZnO, and benzoate derivatives) [70]. Particularly, these
products have been found to be safe and are able to overcome undesirable effects by reducing the
utilization of inorganic and organic compounds [70]. For instance, US patent No. 8,337,820B2
disclosed a water-soluble sunscreen formula, mainly including TiO2 and 5-hydroxy-trytophan
extracted from Griffonia simplicifolia, which can protect individuals with rosacea or other sensitive
skin types from harmful UV radiation. This formulation does cause skin disturbances, such as
inflammation, erythema, and flushing, because it does not contain organic ingredients [71]. In
another study, US patent No. 6,440,402B1 revealed a synergistic absorption effect of Kaempferia
galangal (ginger) root extract upon prolonged exposure to sunlight. It has been suggested that the
topical sunscreen comprising an active agent, a cosmetically vehicle, and sufficient amount of K.
galangal can enhance photostability and sunscreen efficacy [34]. In fact, the Tomato Lycopene (SPF
20) sunscreen from 100% Pure contains a large amount of lycopene that can protect skin from
pollution effects (wrinkles and aging) and provide a moisturizing feeling. The sunscreen of Blossom
Kochhar Aroma Magic has been innovated by taking advantage of the cucumber’s preeminent
features, like the variety of vitamins, and non-greasy and skin-friendly features, to improve
protection effects and prevent visible signs of aging on the skin.
4.2. Sunscreen Combined with DNA Repair Enzymes
There is no denying the fact that UV radiation can penetrate deep into the skin and damage
cells where skin cancer originates [72]. The consequences are considerably enormous while
damaged DNA is unrepaired, especially after decades of repeated damage, including tone loss,
hyperpigmentation, wrinkle formation, and skin cancer [73]. In the early stages, damage appears as
various symptoms, including texture and tone loss, hyperpigmentation, and wrinkle formation. In

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the end stages, skin cancers may result [12,73]. On the other hand, traditional sunscreens only
represent a “passive photoprotection” and are not effective after damaging skin cells due to sun
exposure [73]. Therefore, an “active photoprotection“ approach has been invented by combining
antioxidants and liposome-containing DNA repair enzymes, which could be an advanced photo-
strategy to fill the current gap in sun protection [73].
The topical application of DNA repair enzymes serves to complement the internal DNA repair
mechanisms [73]. The direct repair of damaged DNA using endogenous repair enzymes can reduce
the mutation rates and strengthen the immune response to tumor cells [73]. In order to prevent the
incidence, as well as reduce healthcare expenses in skin treatment, a number of products have
recently focused on not only blocking UV, but also boosting DNA repair and modulating DNA
transcription [72]. The breakthrough DNA repair technology was developed based on
chemopreventive benefits of topical T4 endonuclease (T4N5), photolyase, combining photolyase
with endonuclease, and 8-oxoguanine glycosylase [72] (Table 2). In fact, Emanuele et al. (2013)
successful applied photolyase from Aspergillus nidulans and endonuclease from Micrococcus luteus as
xenogenic DNA repair enzymes to reverse the molecular events related to skin aging and
carcinogenesis due to UV radiation exposure [74]. These enzymes were used to abrogate telomere
shortening and c-FOS gene hyperexpression on the skin, consequently preventing skin aging [74].
In another study, Carducci et al. (2015) compared the protective effects of traditional sunscreen
alone and those of plus DNA repair enzymes in 28 patients with actinic keratosis [75]. Interestingly,
the results indicated that the sunscreen in combination with DNA repair enzymes may outperform
those of traditional in reducing cancerization and UV-related molecular signatures in the patients. It
was suggested that DNA repair enzymes are more effective in preventing malignant transformation
into invasive against squamous cell carcinoma [75].
Table 2. DNA repair enzymes for skin protection application.
DNA Repair
Enzymes Proposal Mechanism and Proven Effects
Topical T4
endonuclease
− Enhancing DNA repair by eliminating cyclobutane pyrimidine dimers
(CPDs) [76]
− Reducing of precancerous and cancerous in high-risk individuals [77]
Photolyase
− Using energy from blue light to quickly repair damaged DNA by
catalyzing electron transfer reactions, resulting in the splitting of
cyclobutane rings [78,79]
− Reducing UV-induced CPDs and precancerous lesions in humans [80]
8-Oxoguanine
glycosylase
− Identifying and initiating repairing DNA photo-lesion (8-oxo-7,8-
dihydroguanine) caused by ROS [81]
− Reducing of UVB-induced tumor progression in mice [82]
4.3. Sunscreen Against Environmental Pollutants
In addition to UV rays, pollutants, such as particulate matter (PM), polyaromatic
hydrocarbons, sulfur oxides (SO2), and nitrogen oxides (NOx), can negatively affect skin. It has been
indicated that these pollutants can induce inflammation, hyperpigmentation, and collagen
breakdown, leading to skin dryness, dark spots, loss of firmness, uneven skin tone, aggravation of
acne, and wrinkle formation [13]. Therefore, manufacturers have countered this issue by
supplementing antioxidant ingredients to cosmetic products that can minimize and prevent side
effects. The protecting mechanism reduces inflammation, prevents particle load on skin by
cleansing or exfoliation, and promotes collagen/elastin synthesis [13]. A few examples of products
which deliver anti-pollution benefits by the above mechanisms are “Dr Dennis Cross Dark Sot Sun
Defense Broad Spectrum SPF 50” with melatonin defense complex and “Clarins UV plus anti-
pollution SPF 50 Broad Spectrum” sunscreen with white tea extract [13]. The Clarins’s product is
believed to help fight pollutants due to its lightweight, oil-free cream, which combines SPF with
extracts from organic cantaloupe and the alpine plant.

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4.4. Sunscreen Against Blue Light
Blue light (380–500 nm) is derived from sunlight or electronic devices such as smartphones,
tablets, and computers [83]. Due to its high energy, it is useful on photodynamic therapy when
using a combination of photosynthesizing drug and a high-intensity light source to treat cancer
[84,85]. However, when blue light enters deep into the skin, it can cause deleterious effects all skin
layers by generating ROS and weakening the epidermal barrier, thereby damaging the extracellular
matrix and accelerating aging [14,15]. Therefore, it is necessary to protect skin against blue light.
Recently, some sunscreen products have improved their ability to protect against blue light, such as
“Sun Expertise (SPF 50+)” and “City Skin Age Defense (SPF 50 and PA+++)” from SKEYDOR and
Murad, respectively. It has been suggested that UV filters can break through the boundaries of UVB
and UVA to continue into the blue light spectrum. UV filters have also been suggested to contain
vitamins and microalgae that can enhance the skin’s defense [14].
4.5. Sunscreen against Thermal IR
IR rays, accounting 54.3% of total solar radiation reaching the Earth, have also been proposed
to be deleterious to human skin [16,86]. Regarding its ability to penetrate the epidermis, dermis,
and subcutaneous tissues, this radiation can be a detrimental factor that damages collagen content
of the skin through the creation of ROS radicals and increased MMP-1 and MMP-9 activity in the
same manner of UV rays [16,86]. Therefore, the application of appropriate antioxidants has been
considered as an effective photoprotective strategy against these impacts. In fact, the IR protection
effectiveness of sunscreen has been investigated through the in vivo method. Kim et al. (2019)
evaluated the resistance to IR rays provided by sunscreen in 155 Korean volunteers, and recorded
the IR reflectance of volunteer’s skin using a benchtop model of an IR light source and a reflectance
measuring probe [87]. The results showed that the infrared protection factor (IPF) in protected skin
was greater than that of unprotected skin. This study also demonstrated good correlation between
IPFs and inorganic sunscreen ingredients in commercial cosmetics [87]. Recently, a number of
defense-IR-protection sunscreens have been launched that offer skin protection from sun damage
and also prevent aging due to chronic exposure to IR. For example, the “Total defense and repair
SPF 34” from Skin Medica is produced using an advanced antioxidant complex. This restorative
formula goes beyond UVA and UVB protection, reducing the appearance of fine lines and wrinkles.
5. Conclusions and Outlook
The use of sunscreen is beneficial in minimizing skin disorders caused by UV radiation and
other factors, especially in people with fair skin. Young adults are regularly advised to use
sunscreen to avoid or minimize photodamaging effects. The FDA also suggests that consumers
should reapply sunscreen (2 mg/cm2) at least every 2 h, or more often if consumers are sweating or
jumping in and out of the water [88]. Many recently produced commercial products contain mot
only conventional active ingredients (TiO2, ZnO, PABA, and salicylates), but also inactive
components (botanicals, vitamins, and hybrid materials). These antioxidants can potentially
eliminate the release of oxidants induced by UV rays and the metallic oxide components in
commercial products. In addition, these products have been developed using a variety of
comprehensive formulations (e.g., emulsion, gel, aerosol, and stick) to provide long-lasting
protection, spreading, moisturizing, and high stability. In addition, these novel products are often
produced by a high number of UV filters combined with botanicals, vitamins, DNA repair
enzymes, and film-forming polymers that can contribute to a higher SPF. Particularly, recent
sunscreens also possess the outstanding capacity to address the demands of consumers to protect
the skin from all environmental aggressors, such as UV rays, pollution, blue light, and IR.
Along with the above-mentioned novel features, sunscreen is currently required to produce
non-sticky or lighter textures that can provide longer-lasting protection, making sunscreen more
convenient in daily routines, especially sport and water activities, and even in warm and humid
climates. Therefore, greater innovations in discovering and synthesizing novel components (e.g.,

Cosmetics 2019, 6, 64 11 of 14
polymers, nanomaterials, and botanicals) and higher demand for lighter emollients are expected to
continue in the future. Besides, manufacturers must overcome current critical challenges, such as
the increasing incidence of melanoma risk, and eczema or photo allergies due to sensitization
reactions between chemicals and the skin, in order to optimize sun protection effect.
Author Contributions: Y.-C.L. planned the study and contributed the main ideas; L.T.N.N. and Y.-C.L. were
principally responsible for the writing of the manuscript; Y.-C.L., V.V.T., D.P., J.-Y.M., and M.C. commented
on and revised the manuscript.
Funding: This work was supported by Basic Science Research Program through the National Research
Foundation of Korea funded by the Ministry of Education (NRF-2017R1D1A1A09000642), by a grant from R &
D program of the Korea Railroad Research Institute (KRRI), Korea, and also by Biocell Korea Co., Ltd.
Conflicts of Interest: The authors declare no conflict of interest.
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