Modern Mild Skin Cleansing

Full text

Journal of Cosmetics, Dermatological Sciences and Applications, 2020, 10, 85-98
https://www.scirp.org/journal/jcdsa
ISSN Online: 2161-4512
ISSN Print: 2161-4105
DOI:
10.4236/jcdsa.2020.102009 Jun. 15, 2020 85 J. Cosmetics, Dermatological Sciences and Applications
Modern Mild Skin Cleansing
Zhengyuan Li
Mill Hill School, Burton Bank Wills Grove, Mill Hill Village, London, UK
Abstract
Surfactant, an abbreviation for the surface-
active agent, is utilized in almost
every industry. It brings two immiscible phases such as oil and water into one
single homogeneous phase, leading to
various industrial applications such as
food, painting, coating, drug delivery as well as cosmetics. The use of surfac-
tants in skin cleansing is very common to keep skin healthy. Their function
herein is to lower the interfacial tension at the dirt/water and skin/water in-
terfaces, thereby detaching dirt, extra sebum or oils from the skin surface. But
this application could bring side effects attributed to the penetration of surfac-
tants into the skin, including skin proteins denaturation, stratum corneum li-
pids removal or even lipids organization disruption in the stratum corneum.
This review summarizes modern mild skin cleansing technologies, which ad-
dress the side effects brought by the surfactants.
Keywords
Mild Cleansing, Skin, Surfactant, Micelle, Polymer
1. Introduction
Nowadays, people pay more attention to their beauty. A woman usually wears
makeup every day, therefore the proper cleansing process afterward is important,
making skin healthy and comfortable.
To keep skin healthy, it is essential to keep the hygiene of the skin by daily
removing dirt, extra sebum, and oils from the skin surface. Since several decades
ago, soap has been one of the most popular cleansing products thanks to its high
foaming ability and strong cleansing power, but there also have been reports of
soap-induced skin irritations such as dry and tight skin [1]-[8]. To avoid aggres-
sive skin cleansing, people currently tend to prefer mild cleansers, which can mi-
nimize the skin barrier damage. Nevertheless, to the best of our knowledge, there
has been a lack of literature summary of modern mild skin cleansing technolo-
gies. To address this issue, a general overview will be given first about the skin
How to cite this paper:
Li, Z.Y. (2020
)
Modern Mild Skin Cleansing
.
Journal
of
Cosmetics
,
Dermatological Sciences and
Applications
,
10
, 85-98.
https://doi.org/10.4236/jcdsa.2020.102009
Received:
February 6, 2020
Accepted:
June 12, 2020
Published:
June 15, 2020
Copyright © 20
20 by author(s) and
Scientific
Research Publishing Inc.
This work is licensed under the Creative
Commons Attribution International
License (CC BY
4.0).
http://creativecommons.org/licenses/by/4.0/
Open Access

Z. Y. Li
DOI:
10.4236/jcdsa.2020.102009 86 J. Cosmetics, Dermatological Sciences and Applications
structure such as epidermis structure and surfactants including their classifica-
tions; followed by a summary of the proposed surfactant penetration models
which are the surfactant monomer penetration model, the surfactant micelle
penetration model and the charge density correlation model; a simple overview
of the two-stage surfactant-protein interaction and the three possible mechanisms
of how surfactants interact with skin lipids; and finally the current approaches to
the formulation of mild cleansers based on the proposed surfactant skin penetra-
tion models and possible mechanisms of surfactant interactions with skin pro-
teins and lipids discussed above [6] [9] [10] [11] [12].
2. Skin Structure
The skin structure can be divided into three parts: hypodermis, dermis and epi-
dermis as shown in Figure 1. The hypodermis is the third layer of the skin, and
is an elastic layer and includes a large amount of fat cells that work as a shock
absorber for blood vessels [13]. The dermis which is above the hypodermis, com-
prises blood vessels, hair follicles, sebaceous glands, and sweat glands [14]. The ep-
idermis is the top layer of the skin, and it is made up of both non-viable epidermis
and viable epidermis (Figure 2). The non-viable epidermis is the stratum corneum
(SC), which can be considered as the barrier to penetration. The layers below the
stratum corneum are viable epidermis which consist of blood capillaries and nerve
fibers. 95% of the total cells in the epidermis are keratinocytes [15].
Figure 1. The skin is composed of three main layers: the epidermis, dermis and the hy-
podermis [15].

Z. Y. Li
DOI:
10.4236/jcdsa.2020.102009 87 J. Cosmetics, Dermatological Sciences and Applications
Figure 2. The structure of skin epidermis [20].
The structure of the stratum corneum can be described as “bricks and mortar”.
There are corneocytes and intercellular lipids in the SC, where the “bricks” are
representing the corneocytes and “mortar” is the intercellular lipids [16] [17] [18]
[19]. The SC is composed of approximately 40% protein, mostly keratin [20].
Cleanser surfactants can bind to SC proteins, leading to transient swelling and
hyperhydration under washing conditions. As water evaporates after washing,
SC proteins will be shrinking, leading to a drying stress [21].
The skin lipids have occupied approximately 10% to 15% of the SC. The major
lipids in the SC are ceramides, which approximately occupied 47%. There are
also cholesterols, fatty acids and cholesterol esters [20]. The physical conformation
of the intercellular lamellar lipids provides a tight and semipermeable barrier to
the passage of water through the tissue. The structural organization as illustrated
in Figure 3 is proposed to account for these observations. The simultaneous pres-
ence of both a crystalline and a liquid crystalline phase is depicted by the domain
mosaic model of SC lipid organization. The fluid phase allows flexibility within
the lipid layer without compromising permeability barriers of the SC [22]. The
packing of the lipids within the bilayers is expected to control the overall barrier
properties. Orthorhombic, hexagonal and fluid bilayers are all proposed forms of
bilayers, among which orthorhombic is the most compact packing with the
highest barrier properties while the fluid form is the least [22] [23].
3. An Introduction to Surfactant
Surfactant, an abbreviation for surface active agent, is an amphiphilic molecule that
has both hydrophilic and hydrophobic/lipophilic parts. In cosmetics, surfactant

Z. Y. Li
DOI:
10.4236/jcdsa.2020.102009 88 J. Cosmetics, Dermatological Sciences and Applications
Figure 3. The skin lipids structural organization [24].
is commonly used as a detergent in facial cleansing. The function herein is to
lower the interfacial tension at the dirt/water and skin/water interfaces, there-
by detaching the dirt from the skin surface. The dirt can also be removed in an
emulsified form [24]. Surfactants tend to form aggregates called micelles, where
the surfactants hydrophobic groups are directed towards the interior of the clus-
ter and the polar heads are directed towards water. The micelle is a polar aggre-
gate of high-water solubility without much surface activity. It is only the surfac-
tant monomers that are capable of lowering surface tension [1] [6] [7] [24] [25]
[26] [27].
Surfactants can be classified into four groups based on the charge presented
on the polar groups after dissociation in the aqueous solution: anionic, cationic,
non-ionic and amphoteric.
Anionic Surfactant
Anionics are the most common used surfactant, occupying about 60% annual
worldwide surfactant production. Their hydrophilic heads possess negative charges.
Anionic surfactants have strong cleansing power, good wetting properties and
excellent lather characteristic, but they are considered to be irritated to the skin
and eyes [1] [2]. The examples of the most commonly used anionic surfactants
are soap, sodium lauryl sulphate (SLS), and sodium laureth sulphate (SLES). Soap
is still the largest single type of surfactant, which is a generic name representing
the alkali metal salts of carboxylic acids derived from animal fats or vegetable oils.

Z. Y. Li
DOI:
10.4236/jcdsa.2020.102009 89 J. Cosmetics, Dermatological Sciences and Applications
Perhaps the most famous soap cleanser on the market is Shiseido Senka Perfect
Whip Cleansing Foam. SLS is a well-known wetting agent and a detergent, which
has been proven to irritate the skin leading to the skin barrier damage as well.
SLES is the primary surfactant in commercial body wash, shower gel and sham-
poo, owing to its good cleansing power and low cost. The commercial examples
containing SLES are Lush I Love Juicy Shampoo and La Roche-Posay Effaclar
Purifying Foaming Gel Cleanser. However, SLES also has some irritant potential
to the skin [3] [4] [5]. Anionic surfactant is normally used as a primary surfactant,
thanks to its moderate cost, and more importantly the irritation potential can be
reduced in the formulation by mixing the anionic surfactant with polymers and
other types of surfactants [6] [7] [8].
Cationic Surfactant
Cationic surfactants are positively charged, and have lower deterging power
than that of anionic surfactants, however, they can be used as antimicrobial pre-
servatives due to the considerable bactericidal activity against a wide range of mi-
croorganisms [26]. The examples of the most commonly used cationic surfactant
are amine salts and quaternary ammonium salts [28]. For example, Cetrimonium
Bromide is used in Bioderma Sensibio Micellar Water.
Nonionic Surfactant
Nonionic surfactant is the second largest surfactant groups, and has no elec-
trical charge on its head, so it is normally compatible with all other types of sur-
factant. The nonionic surfactants are also used as thickeners for shampoos, as
emulsifiers and suspending agents in cosmetics, pharmaceuticals and foods [29].
The nonionic surfactants are regarded as the lowest irritants to the skin [2], which
is why they are often formulated in eye makeup removers such as PEG-6 Ca-
prylic/capric glycerides in Bioderma Sensibio Micellar Water. The physicochemi-
cal properties of the ethoxylated compounds are very temperature dependent.
Non-ionic surfactants containing polyoxyethylene chain exhibit reverse solubili-
ty versus temperature in water. As temperature rises, the interactions between
the oxyethylene groups and water become weaker, therefore two phases even-
tually appear. The temperature at which it occurs is called the cloud point. The
cloud point mainly depends on the number of oxyethylene units while the hy-
drophobic chain length has a less influence [2].
Amphoteric surfactant
Amphoteric surfactants usually contain two charged groups with different signs.
An amphoteric surfactant is one that changes from net cationic via zwitterionic
to net anionic ongoing from low pH to high pH. The change in pH naturally af-
fects surfactant properties such as foaming, wetting, detergency and etc. Am-
photeric surfactants are mild to skin and also exhibit low eye irritation and are
frequently used in shampoos and other cosmetic products. For instance, Co-
co-betaine was formulated together with SLES in La Roche-Posay Effaclar Puri-
fying Foaming Gel Cleanser to improve its skin mildness. However, their appli-
cation sometimes is restricted by their high costs [30].

Z. Y. Li
DOI:
10.4236/jcdsa.2020.102009 90 J. Cosmetics, Dermatological Sciences and Applications
General physicochemical properties of surfactant
There are many physicochemical properties of surfactants, and one of the
most important characteristics is the critical micelle concentration (CMC). CMC
is the concentration of the surfactant above which micelles are spontaneously
formed [31]. When the concentration is below the CMC, the surfactant molecule
that has been added into the water will arrange on the air-water interface, with
the hydrophobic part facing toward the air. As the added surfactant concentra-
tion reaches a certain level, there is no space for the rest surfactant to be placed
at the interface, therefore, the molecules start to form aggregates, which is called
micelles. Any further addition of the surfactants after reaching CMC will only
increase the number of micelles in the aqueous phase. The surfactant molecule
that has been placed on the interface is called monomer, and only monomers
have surface activity, meaning only monomers could lower the surface tension
between two phases, so beyond the CMC, there is no further reduction in the
interfacial tension. Usually anionic and cationic surfactants have higher CMCs
than those of nonionic surfactants, due to the fact that the charge degree of the
hydrophilic group could influence the CMC value [10] [28] [30].
Another interesting characteristic of the surfactant is the packing geometry.
The surfactant structure formed is as a result of the balance between the polar
and the non-polar part of the surfactant molecule. The critical packing parame-
ter (CPP) can be seen as the ratio between the cross-sectional area of the hydro-
phobic part and that of the hydrophilic head part. When the CPP is smaller than
1, it can be arranged as a normal micelle, normal discontinuous cubic, normal
hexagonal, or normal bicontinuous cubic. When the CPP is equal to 1, it usually
forms a lamellar phase. When the CPP is greater than 1, it can form reverse hex-
agonal, reverse discontinuous cubic, or reverse micelle [32].
4. Surfactant Skin Penetration Models
There are three generally accepted models that have partially explained the me-
chanisms behind surfactant penetrating into skin.
The Surfactant Monomer Skin Penetration Model
The monomer penetration model is the most commonly accepted model, as it
regards that only surfactant monomers could penetrate into the skin, either be-
cause that only surfactant monomers are surface active or the micelles are too
big to pass through the skin barrier [1] [6] [33]. This view is based on experimen-
tal observations which a correlation between the amount of surfactant monomers
that have been added in and the damage level of the skin has been shown [12]
[33] [34]. It is widely accepted that the surfactants need to penetrate into the SC
and then induce irritation. However, if the surfactant monomer skin penetration
model is always true, the level of penetrated surfactant should reach a maximum,
which is at the CMC of the surfactant. As a result, surfactant concentration beyond
the CMC would have no effects on the contribution of surfactant-induced skin
irritation. However, it is well-known that the surfactant-induced skin irritation
exacerbates as the total surfactant concentration increases beyond the CMC [12].

Z. Y. Li
DOI:
10.4236/jcdsa.2020.102009 91 J. Cosmetics, Dermatological Sciences and Applications
The Surfactant Micelle Skin Penetration Model
To rationalize the observed dose-dependent effect of the surfactant-induced
irritation, researchers proposed that: 1) the monomer activity increased beyond
the CMC, and 2) the micelles solubilized lipids present in the skin. In contrast, it
was found out that the surfactant monomer activity does not increase but slightly
decreases beyond the CMC. In addition, an increase in the number of micelles
above the CMC demonstrates an increase in the lipid solubilization capacity, but
it could not explain the observed enhanced surfactant penetration into skin [31].
Therefore, a more complex mechanism has been proposed. It was suggested that
not only surfactant monomers but also some micelles are able to penetrate into
the skin [35]. Moore
et al.
[31] carried out an investigation whether an increase
in the total SDS concentration above the CMC in the contacting solution would
lead to an increase in the SDS concentration in the epidermis. The results showed
that there was a linear relationship between the SDS concentration in the con-
tacting solution and the SDS concentration in the epidermis, contradicting the
view of surfactant monomer skin penetration model [31].
Surfactant micelle penetration model is thus proposed. To consider the mi-
celle penetration model, it is necessary to consider the micelle size relative to the
radius of aqueous pore in the skin barrier, therefore it is interesting to examine
the effect of adding poly (ethylene oxide) (PEO) to the surfactant solution. In the
presence of PEO, the SDS concentration in the epidermis has been reduced sig-
nificantly [31]. This was due to that the PEO could bind to the SDS micelles, and
form micelle-like complexes with SDS, which have a relatively larger size than
that of the SDS micelles. The larger PEO-bonded micelles were postulated to be
hindered by the aqueous pores, thereby reducing SDS skin penetration [31]. The
researchers also studied SDS micelles skin penetration by mixing SDS with the
ethylene oxide type non-ionic surfactants (CmEn) [31], and they discovered that
the SDS from the SDS/CmEn mixtures is less able to penetrate into the skin than
that from the pure SDS solution. By using the dynamic light scattering technique,
they revealed that the SDS/CmEn mixed micelles had larger sizes than those of the
pure SDS micelles, and hence the increase in the micelle size reduced the surfac-
tant penetration into the skin was proposed [31].
Glycerin is a well-known humectant and skin beneficial agent. An investiga-
tion on whether the addition of glycerin would reduce the SDS micelle skin pe-
netration was carried out. It was shown that the addition of 10 wt% glycerin to
the SDS solution did not reduce its CMC or micelle size. On the other hand, with
the addition of 10 wt% glycerin, the size and the number density of the aqueous
pores in the SC were reduced, suggesting that the SDS micelles were sterically
hindered to penetrate [34].
Sodium cocoyl isethionate (SCI) is a very important surfactant that has been
using in facial cleansers and body washes, attributed to its mild, less irritate cha-
racteristics to the skin. One of the reasons accounting for the mildness of SCI
was the incapability of its micelles to contribute to the skin penetration. It was
shown that the SCI micelles have a significant larger size than that of the skin

Z. Y. Li
DOI:
10.4236/jcdsa.2020.102009 92 J. Cosmetics, Dermatological Sciences and Applications
aqueous pores, suggesting that it is unfavorable for the SCI micelles to penetrate
into the skin and induce further irritation (Table 1) [36]. Ananthapadmanabhan
et al.
[29] observed that the CMC of SCI is lower than that of SDS, and binds to
proteins only about one fifth as much as the SDS does under similar conditions
and exposure time, which has proved that monomer penetration model is cor-
rect in this way [37].
Charge Density Correlation Model
The mechanisms of anionic surfactant penetration into skin are still widely
debated. Neither the monomer penetration model nor the micelle penetration
model could fully explain how anionic surfactant penetrates into the skin. A new
hypothesis is proposed in which short-term penetration is based on monomer
concentration and longer-term penetration is based on surfactant-induced damage
to the skin barriers [36]. A strong correlation was found between the amount of
penetrated anionic surfactants and the Zeta potential of the surfactant solutions.
When an anionic surfactant solution contacts with the skin, monomers pene-
trate into the skin, bind to proteins and increase the charge on protein network-
ing, leading to swelling of the structure. This allows progressive surfactant bind-
ing in even deeper skin layers, leading to further structural swelling and surfac-
tant penetration [36]. As the damage to the skin increases, it is possible for mi-
celles and small surfactant aggregates to penetrate, leading to further swelling of
the structures. The more negative charged surfactant system, the longer the sur-
factant exposure time, more bindings could occur, resulting in more swelling of
the structures. These structures are likely to have a charge characteristic propor-
tional to micelle-like structures, which could explain the correlation between the
Zeta potential and the micelle penetration. Interestingly, their data did not show
a strong correlation between the micelle size and surfactant penetration. The less
skin penetration of SDS micelles with PEO was hypothesized to be attributed to
the lower diffusion speed [38].
5. Interaction between Surfactant and Proteins/Lipids
Protein are copolymers built up of amino acids that contain polar and non-polar
groups. The polar groups cloud be ionic or non-ionic, which may also vary with
pH, thus protein can be seen as an amphoteric polyelectrolyte with some hydro-
phobic groups or as an amphiphilic polymer with a variable charge density. It has
occupied approximately 40% of the SC [31].
Table 1. Skin aqueous pore characteristic resulting from skin exposure to three solutions
[32].
Types of aqueous
contacting
solution
Average aqueous
pore radius
Rpore (A)
Normalized pore
number density
(E/T) normal
Micelle radius
(A)
Critical micelle
concentration,
CMC (mM)
a) SCI
29 ± 5
2 ± 1
33.5 ± 1
1.0
b) SDS
33 ± 5
7 ± 1
19.5 ± 1
8.7
c) PBS Control
20 ± 3
1
N/A
N/A

Z. Y. Li
DOI:
10.4236/jcdsa.2020.102009 93 J. Cosmetics, Dermatological Sciences and Applications
There are two stages of binding between surfactant and water-soluble protein:
site-specific binding and co-operative binding. Site-specific binding is the sur-
factant binds to sites on the protein for which there is favourable interaction be-
tween the surfactant and the site. An example for this is the binding of an anio-
nic surfactant to positively charged amino acid group on the protein. The sites on
the protein relative to the total number of side chains, which forms one-to-one
specific interactions [39].
Surfactants such as non-ionic surfactants do not go through site specific inte-
ractions with the protein, due to the fact that interactions are not free energeti-
cally favourable. Those surfactants interact with the protein through another
stage which is called cooperative binding. In cooperative binding, the surfactant
molecules aggregate to form micellar structures that interact with the protein.
This interaction takes place and corresponds to the protein unfolding and losing
its secondary structure [39].
To reduce the protein bindings, a bulky non-ionic surfactant is favorable due
to: 1) the protein backbone shields exposed hydrophobic patches at the hydro-
phobic core-water micellar interface from the aqueous environment surround-
ing the micelle. A large head group will shield and reduce the hydrophobic sur-
face area of the micelle core exposed to water, thus reducing the driving force for
protein backbone to bind to the surface, by increasing the steric interactions be-
tween the protein and the surfactant heads; 2) the hydrophobic protein side chains
are able to penetrate into the hydrophobic core of the micelle. The large hydro-
philic heads of the non-ionic surfactants should also sterically hinder the access
of the hydrophobic protein side chains into the micellar interior, thus reducing
the strength of the interactions. In addition, it has been found that the reduction
in the micelle surface charge density could make the electrostatic interactions
less favourable, thereby mixing anionic surfactants with non-ionic surfactants is
a common method to reduce surfactant bindings to proteins [39].
It is recognized that the lipid organization controls the skin absorption of ex-
ogenous substances, therefore, any damage to the lipid organization could lead
to an alteration of the skin barrier [32]. The skin lipid phases consist in a lamellar
structure made of stacks of lipid bilayers. Fluid phase is the most permeable phase
in their molten state, whereas there are two solid crystalline phases: the orthor-
hombic phase (OR) and the hexagonal phase (HEX) [28]. As the damage to the
skin barrier increases, the organization of the lipids will be more likely shifted to
the liquid crystalline phase [40].
There are three possible mechanisms of surfactants interacting with the SC li-
pids: 1) removal of the surface lipids by the detergent action of surfactants; 2)
disorganization of the SC by mixing with surfactants. This happens when the sur-
factants mix with lipids in the SC, which will distort the organization of the li-
pids; 3) solubilization and extraction of the SC lipids into the surfactant solution.
The surfactant monomers penetrate into the SC and insert in the lipid bilayer
followed by micellar solubilization of cholesterol, free fatty acids and fatty esters
[41].

Z. Y. Li
DOI:
10.4236/jcdsa.2020.102009 94 J. Cosmetics, Dermatological Sciences and Applications
Investigation was carried on about how different types of surfactant contri-
buted to the removal of different types of skin lipids. SLS, sodium stearoyl lacty-
late (SSL), cetyl trimethyl ammonium chloride (CTAC), distearyldimonium chlo-
ride (DC), laureth-23, PEG-25 hydrogenerated castor oil, PEG-100 stearate,
PEG-12 dimenthicone, Polyoxyethylene sorbitan laurate (polysorbate) and hy-
drogenated lecithin were examined to remove various model skin lipids such as
squalene, triglycerides (TG), ceramides and cholesterol [41]. The results showed
that different surfactants can remove different types of lipids in the skin. For SLS,
there was a significant decrease in squalene and n-alkane; for SLS and CTAC,
there was a significant decrease of TG. All surfactants induced an increase of the
polar component of the skin except PEG-12 dimethicone and polysorbate. SLS,
CTAC, and DC were significant on removing ceramides and TG. Ceramide le-
vels became less than 3 times lower than TG after the surfactant treatment. No
surfactant removed a significant high level of cholesterol [41]. PEG-12 dimethi-
cone and polysorbate are exception of inducing an increase of the polar compo-
nents in the skin, indicating they are mild to the skin. The structural transition
of lipid bilayer from the orthorhombic phase to the hexagonal phase was detected
whereas the disorganization to the liquid crystalline phase was not observed.
Polysorbate and PEG-12 dimethicone were identified as the mildest surfactants
in this study, probably thanks to their large PEG headgroups, suggesting that
bulky PEG headgroup inhibited the penetration of these surfactants into the SC
lipid matrix [40].
6. Modern Mild Cleanser Formulation
Recent researches and applications have provided more information on the in-
teractions between surfactants and skin, which helps the industry develop tech-
nologies that can produce cleansers that are both functional and mild. Liquid
cleansers usually have a combination of anionic and amphoteric surfactants along
with high levels of oils and occlusive as moisturizers, in order to reduce the pro-
tein denaturation and skin barrier damage [29]. However, the addition of ampho-
teric surfactants cannot solve the problem completely, a certain degree of skin li-
pids damage still occurs. The ratio between anionic and amphoteric surfactants
also needs to be considered. The current moisturizing shower gels usually use
moisturizing oils and humectants at a very high concentration, even though most
of them will be washed away during rinsing [37]. Nowadays, the cleansers often
use a combination of mild surfactant systems and efficient natural emollient oils,
lipids, occlusive, as well as humectants.
Skin dryness is one of the common problems caused by cleansers, and it is
usually addressed by occlusives, emollients and/or humectants. Petrolatum act as
an occlusive barrier, reducing the evaporation of the water inside the skin. Liq-
uid triglyceride oils can penetrate into skin cracks and crevices, and moisturize
the deeper skin layers. More importantly it can also prevent surfactants from in-
teracting with the skin proteins [37]. Glycerol is used as a humectant to retain

Z. Y. Li
DOI:
10.4236/jcdsa.2020.102009 95 J. Cosmetics, Dermatological Sciences and Applications
skin moisture, however, due to its high-water solubility, the addition of glycerol
in cleansers becomes inefficient, because a large amount of glycerol will be lost
during wash. Simple addition of petrolatum and triglycerides in cleansers is fac-
ing this problem as well. The industry uses long-chain fatty acids (C16-C18) to
lower the tendency of a surfactant system to damage lipid membranes. This is
perhaps due to their ability to act as a buffer against lipid extraction by surfac-
tant micelles, and to deposit and to replenish some of the fatty acid lipids lost
during cleansing, which makes the cleanser milder [21].
The use of polymers to make milder cleansers is an alternative approach. Po-
lyethylene oxide (PEO) has been shown to alter micelles and reduce the aggres-
siveness of surfactants [42]. The PEO chains bind water molecules and the sur-
factant monomers, increasing the sizes of the micelles, thereby sterically hinder-
ing the micelle penetration into skin. More recently, hydrophobically modified
polymers (HMPs) have been used instead of PEO. HMPs can associate with sur-
factants in solutions. Surfactant self-assembled to the hydrophobic domains of
the HMPs, results in slower surfactant dynamics [37]. In addition, thanks to the
larger sizes of the surfactants, less surfactants can penetrate into the SC, making
the cleanser less aggressive. A gentle facial cleanser with HMPs was developed by
researchers in Johnson & Johnson, and the clinical test results demonstrated that
HMPs do minimize the SC disruption [37].
7. Conclusion and Perspectives
The focus of this review paper is to summarize the state of the art understand-
ings of modern mild skin cleansing technologies. Anionic surfactants have good
lathering and cleansing properties making them the ideal ingredients in cleanser
formulations, on the other hand, anionic surfactants have small micelle size and
high charge density, potentially contributing to the skin irritation induced by sur-
factants. To address this issue, addition of non-ionic/amphoteric surfactants to the
cleanser formulation can reduce the micelle charge density and sterically hinder
the micelle-skin protein binding, making the cleanser less harsh to the skin. In
addition, adding polymers to the surfactant system further increases the micelle
size and decreases the micelle diffusion speed, thereby hindering surfactant pe-
netrating into skin. Last but not the least, incorporation of humectants, emollients
as well as occlusive into the surfactant system in the cleanser formulation can
either reduce the surfactant skin penetration, or lower the surfactant system da-
maging the skin lipids, thereby minimizing the occurrence of skin irritation.
Acknowledgements
The author is grateful for the opportunities provided by Mill Hill School in Lon-
don, UK and the ViaX Online Education Platform.
Conflicts of Interest
The author declares no conflicts of interest regarding the publication of this pa-
per.

Z. Y. Li
DOI:
10.4236/jcdsa.2020.102009 96 J. Cosmetics, Dermatological Sciences and Applications
References
[1] Ananthapadmanabhan, K.P., Yu, K.K., Meyers, C.L. and Aronson, M.P. (1996)
Binding of Surfactants to Stratum Corneum.
Journal of the Society of Cosmetic
Chemists
, 47, 185-200.
[2] Strube, D.D., Koontz, S.W., Murahata, R.I. and Theiler, R.F. (1989) The Flex Wash
Test: A Test Method for Evaluating the Mildness of Personal Washing Products.
Journal of the Society of Cosmetic Chemists
, 40, 297-306.
[3] Imokawa, G. (1997) Surfactant Mildness. In: Rieger, M.M. and Rhein, L.D., Eds.,
Surfactants in Cosmetics
, Marcel Dekker, New York, 427-471.
[4] Scheuplein, R. and Blank, I. (1971) Permeability of the Skin.
Physiological Reviews
,
51, 702-747. https://doi.org/10.1152/physrev.1971.51.4.702
[5] Abraham, W. (1997) Surfactant Effects on Skin Barrier. In: Rieger, M.M. and Rhein,
L.D., Eds.,
Surfactants in Cosmetics
, Marcel Dekker, New York, 437-487.
[6] Faucher, J.A. and Goddard, E.D. (1978) Interaction of Keratinous Substrates with
Sodium Lauryl Sulfate. I. Sorption.
Journal of the Society of Cosmetic Chemists
, 29,
323-337.
[7] Faucher, J.A. and Goddard, E.D. (1978) Interaction of Keratinous Substrates with
Sodium Lauryl Sulfate. II. Permeation through Stratum Corneum.
Journal of the
Society of Cosmetic Chemists
, 29, 339-353.
[8] Rhein, L.D. and Sireion, F.A. (1991) Surfactant Interactions with Skin. In: Bender,
M., Ed.,
Interfacial Phenomena in Biological Systems
,
Surfactant Science Series
, Vol.
39, CRC Press, Boca Raton, 33-49.
[9] Hama, I., Sasamoto, H., Tamura, T., Nakamura, T. and Miura, K. (1998) Skin
Compatibility and Ecotoxicity of Ethoxylated Fatty Methyl Ester Nonionics.
Journal
of Surfactants and Detergents
, 1, 93-97. https://doi.org/10.1007/s11743-998-0012-8
[10] Rhein, L.D., Robbins, C.R., Fernee, K. and Cantore, R. (1986) Surfactant Structure
Effects on Swelling of Isolated Human Stratum Corneum.
Journal of the Society of
Cosmetic Chemists
, 37, 125-139.
[11] Imokawa, G., Sumura, K. and Katsumi, M. (1975) Study on Skin Roughness Caused
by Surfactants: II. Correlation between Protein Denaturation and Skin Roughness.
Journal of the American Oil Chemists
’
Society
, 52, 484-489.
https://doi.org/10.1007/BF02640737
[12] Hall-Manning, T.J., Holland, G.H., Rennie, G., Revell, P., Hines, J., Barratt, M.D.
and Basketter, D.A. (1998) Skin Irritation Potential of Mixed Surfactant Systems.
Food and Chemical Toxicology
, 36, 233-238.
https://doi.org/10.1016/S0278-6915(97)00144-0
[13] Evert, R.F. (2006) Esau’s Plant Anatomy: Meristems, Cells, and Tissues of the Plant
Body—Their Structure, Function, and Development. 3rd Edition, Wiley, Hoboken,
NJ. https://doi.org/10.1002/0470047380
[14] Keleb, E., Sharma, R.K., Mosa, E.B. and Aljahvi, A.Z. (2010) Transdermal Drug De-
livery System-Design and Evaluation.
International Journal of Advances in Phar-
maceutical Sciences
, 1, 201-211.
[15] Lumenlearning, Module 24: The Integumentary System, Structure and Function of
the Skin.
https://courses.lumenlearning.com/wmopen-biology2/chapter/structure-and-functi
on-of-skin/
[16] Elias, P.M. (1981) Lipids and the Epidermal Permeability Barrier.
Archives of Der-
matological Research
, 270, 95-117. https://doi.org/10.1007/BF00417155
[17] Wertz, P.W. and Downing, D.E. (1989) Stratum Corneum: Biological and Bio-

Z. Y. Li
DOI:
10.4236/jcdsa.2020.102009 97 J. Cosmetics, Dermatological Sciences and Applications
chemical Considerations. In: Hadgraft, J. and Guy, R.H., Eds.,
Transdermal Drug
Delivery
:
Developmental Issues and Research Initiatives
, Marcel Dekker, New York,
1-22.
[18] Bronaugh, R.L. and Maibach, H.I. (1985)
In Vitro
Models for Human Percutaneous
Absorption. In: Maibach, H.I. and Lowe, N.J., Eds.,
Models in Dermatology
, Vol. 2,
Karger, Basel, 178-188.
[19] Heisig, M., Lieckfeldt, R., Witturn, G., Mazurkevich, G. and Lee, G. (1996) Non
Steady-State Descriptions of Drug Permeation through Stratum Corneum. I. The
Biphasic Brick-and-Mortar Model.
Pharmaceutical Research
, 13, 421-426.
https://doi.org/10.1023/A:1016048710880
[20] https://images.wisegeek.com/anatomy-of-the-epidermis.jpg
[21] Lips, A., Ananthapadmanabhan, K.P., Vethamuthu, M.,
et al.
(2006) Role of Surfac-
tant Micelle Charge in Protein Denaturation and Surfactant Induced Skin Irritation.
In: Rhein, L.D., Schlossman, M., O’Lenick, A. and Somasundaran, P., Eds.,
Surfac-
tants in Personal Care Products and Decorative Cosmetics
, CRC Press, Boca Raton,
177-187.
[22] Ananthapadmanabhan, K.P.,
et al.
(2009) A Novel Technology in Mild and Moistu-
rizing Cleansing Liquids.
Cosmetic Dermatology
, 22, 307-316.
[23] Vreeken, R.J.
https://www.researchgate.net/figure/Lamellar-and-lateral-organization-in-human
stratum-corneum-1-The-outermost-layer-of_fig4_231613918
[24] Vilaplana, J., Mascaro, J.M., Trullas, C., Coil, J., Romaguera, C., Zemba, C. and Pe-
lejero, C. (1992) Human Irritant Response to Different Qualities and Concentra-
tions of Cocoamidopropylbetaines: A Possible Model of Paradoxical Irritant Re-
sponse.
Contact Dermatitis
, 26, 289-294.
https://doi.org/10.1111/j.1600-0536.1992.tb00120.x
[25] Brito, R.O., Silva, S.G., Fernandes, R.M., Marques, E.F., Enrique-Borges, J. and do
Vale, M.L. (2011) Enhanced Interfacial Properties of Novel Amino Acid-Derived
Surfactants: Effects of Headgroup Chemistry and of Alkyl Chain Length and Unsa-
turation.
Colloids and Surfaces B
:
Biointerfaces
, 86, 65-70.
https://doi.org/10.1016/j.colsurfb.2011.03.017
[26] Wilhelm, K.-P., Cua, A.B., Wolff, H.H. and Maibach, H.I. (1993) Surfactant-Induced
Stratum Corneum Hydration
in Vivo
: Prediction of the Irritation Potential in
Anionic Surfactants.
Journal of Investigative Dermatology
, 101, 310-315.
[27] Loden, M. (1990) The Simultaneous Penetration of Water and Sodium Lauryl Sul-
fate through Isolated Human Skin.
Journal of the Society of Cosmetic Chemists
, 41,
227-233.
[28] Robbins, C.R. and Fernee, K.M. (1983) Some Observations on the Swelling Behavior
of Human Epidermal Membranes.
Journal of the Society of Cosmetic Chemists
, 34,
21-34.
[29] Ananthapadmanabhan, K.P., Moore, D.J., Subramanyan, K.,
et al
. (2004) Cleansing
without Compromise: The Impact of Cleansers on the Skin Barrier and the Tech-
nology of Mild Cleansing.
Dermatologic Therapy
, 17, 16-25.
https://doi.org/10.1111/j.1396-0296.2004.04S1002.x
[30] Putterman, G.J., Wolejsza, N.F., Wolfram, M.A. and Laden, K. (1997) The Effect of
Detergents on Swelling of Stratum Corneum.
Journal of the Society of Cosmetic
Chemists
, 28, 521-532.
[31] Moore, P.N., Puvvada, S. and Blankschtein, D. (2003) Challenging the Surfactant
Monomer Skin Penetration Model: Penetration of Sodium Dodecyl Sulfate Micelles
into the Epidermis.
Journal of Cosmetic Science
, 54, 29-46.

Z. Y. Li
DOI:
10.4236/jcdsa.2020.102009 98 J. Cosmetics, Dermatological Sciences and Applications
[32] Damien, F. and Boncheva, M. (2010) The Extent of Orthorhombic Lipid Phases in
the Stratum Corneum Determines the Barrier Efficiency of Human Skin
in Vivo
.
Journal of Investigative Dermatology
, 130, 611-614.
https://doi.org/10.1038/jid.2009.272
[33] Li, J., Dahanayake, M., Reierson, R.L. and Tracy, D.J. (1999) Amphoteric Surfac-
tants Having Multiple Hydrophobic and Hydrophilic Groups. U.S. Patent 5914310.
[34] Myers, D. (2006) Surfactant Science and Technology. 3rd Edition, John Wiley &
Sons, Inc., Hoboken, NJ. https://doi.org/10.1002/047174607X
[35] Agner, T. and Serup, J. (1990) Sodium Lauryl Sulphate for Irritant Patch Test-
ing—A Dose-Response Study Using Bioengineering Methods for Determination of
Skin Irritation.
Journal of Investigative Dermatology
, 95, 543-547.
[36] Ghosh, S. and Blankschtein, D. (2007) Why Is Sodium Cocoyl Isethionate (SCI)
Mild to the Skin Barrier?—An
in Vitro
Investigation Based on the Relative Sizes of
the SCI Micelles and the Skin Aqueous Pores.
Journal of Cosmetic Science
, 58,
229-244.
[37] Draelos, Z., Hornby, S., Walters, R.M. and Appa, Y. (2013) Hydrophobically Mod-
ified Polymers Can Minimize Skin Irritation Potential Caused by Surfactant-Based
Cleansers.
Journal of Cosmetic Dermatology
, 12, 314-321.
https://doi.org/10.1111/jocd.12061
[38] Ananthapadmanabhan, K.P. (1993) Protein-Surfactant Interactions. In: Goddard,
E.D., Ed.,
Interactions of Surfactants with Polymers and Proteins
, CRC Press, Boca
Raton, 319. https://doi.org/10.1201/9781351073783-9
[39] Janssens, M., van Smeden, J., Gooris, G.S.,
et al.
(2011) Lamellar Lipid Organization
and Ceramide Composition in the Stratum Corneum of Patients with Atopic Ecze-
ma.
Journal of Investigative Dermatology
, 131, 2136-2138.
https://doi.org/10.1038/jid.2011.175
[40] Lemery, E.,
et al.
(2015) Surfactants Have Multi-Fold Effects on Skin Barrier Func-
tion.
European Journal of Dermatology
, 25, 424-435.
https://doi.org/10.1684/ejd.2015.2587
[41] Fluhr, W., Bornkessel, A. and Berardesca, E. (2006) Glycerol Just a Moisturizer? Bi-
ological and Biophysical Effects. In: Loden, M. and Maiback, H.I., Eds.,
Dry Skin
and Moisturizers
, CRC Press, Boca Raton, FL, 227-244.
[42] Moore, P.N., Puvvada, S. and Blankschtein, D. (2003) Role of the Surfactant Polar
Head Structure in Protein-Surfactant Complexation: Zein Protein Solubilization by
SDS and by SDS/C12E
n
Surfactant Solutions.
Langmuir
, 19, 1009-1016.
https://doi.org/10.1021/la020613k