Evaulation of irritation potential of surfactant mixtures

Irritation potential of sodium laureth sulfate (SLES) alone, and in combination with lauryl glucoside (LG), polysorbate 20 (PS) and cocoamidopropyl betaine (CAPB) was tested in 13 human subjects. Four main and six sub-formulations were prepared and evaluated. Formulations were applied to the forearm as a 24 h close patch study. Irritation was scored by two different methods using an in vivo clinical protocol based on visual scoring and on the stratum corneum capacitance measurement. Irritation was found to be dose dependent. At 2 mg/patch level ten subjects did not show any skin reaction. At 20 mg/patch level eleven subjects showed a broad range of skin irritation. The highest irritation was observed with the formula that contained SLES, LG, and cocamide DEA together. Among the sub-formulations, cocamide DEA showed the highest irritation grade. A statistically significant correlation was observed between visual, clinical and corneometer scores. It was concluded that the irritation potential of surfactants was related to the total surfactant concentration, application mode, and the thermodynamic activity of molecules in the solution as well as the chemical structure of the surfactant molecules.     

Confocal Raman microspectroscopy of stratum corneum: a pre-clinical validation study

Skin moisturization is not only important for maintaining skin functional properties but also has great impact on the skin's aesthetic properties. The top layer of the skin, the stratum corneum (SC), plays a key role in protecting and preventing against external aggressions as well as in regulating water flux in and out. Confocal Raman microspectroscopy is the first commercially available technique that provides a non-invasive, in vivo method to determine depth profiles of water concentration in the skin, however, in this case it was applied in an in vitro setting. As the first phase of validating the usefulness of confocal Raman microspectroscopy, we used porcine skin as a surrogate for human skin. Water concentration profiles were obtained using confocal Raman microspectroscopy from isolated pigskin SC and compared with that using the Karl Fischer titration method. The two methods correlated very well with a regression coefficient of 1.07 as well as a correlation coefficient, R(2) = 0.989, which demonstrated the consistency and accuracy of confocal Raman microspectroscopy for water concentration determination. To evaluate the instrument's response to different skin care/cleansing products, a wide range of products were tested to compare their skin moisturization ability. Among those tested were a lotion, commercial soap bar, syndet bar, traditional non-emollient shower gel (water, Sodium Laureth Ether Sulfate (SLES), cocamidopropyl betaine system) and emollient containing shower gel (water, sunflower oil, SLES, cocamidopropyl betaine, glycerin, petrolatum). The results were consistent with what was expected. The water content on skin treated with (A) lotion was significantly higher than the non-treated control; (B) syndet bar-treated skin had a significantly higher water content than soap-based bar-treated sites; (C) non-emollient shower gel washed sites were more moisturized than soap-based bar-treated samples; and (D) emollient shower gel-treated skin was significantly more hydrated than non-emollient shower gel washed skin. The unique and direct quantitative water content information provided by confocal Raman microspectroscopy offers a whole new perspective for fundamental skin moisturization studies and will play an important role in evaluating moisturizing profiles and the hydration potential of products designed for personal care in the cosmetic industry.     

Infrared spectroscopy of the skin: influencing the stratum corneum with cosmetic products

The stratum corneum is the outermost layer of the skin and, as such, represents the decisive barrier between the body and the environment. The combination of horny cells and lamellar lipid layers prevents water loss from the body and protects it against penetration by exogenous substances. For selective investigation of the thin outermost stratum corneum layer ATR-FTIR (attenuated total reflection Fourier transform infrared) spectroscopy has proved itself in practice. It provides information about the sebum content, type of fatty substances, water content and degree of order of the lamellar lipid film in the stratum corneum. Different types of skin (dry, normal and greasy) differ mainly in their sebum content but also in the composition of their fats and the degree of order of their lipids. A comparison with model lipid mixtures shows that the stratum corneum lipids are mainly present in a fixed gel form under physiological conditions. In cleansing processes a large part of the sebum is removed from the skin. The skin reacts to the defatting process by the rapid secretion of sebum. After cleansing with a mild face cleansing emulsion the re-achievement of the same fat status takes longer than with a surfactant shower gel. Skin creams cause alterations to the skin moisture and in the degree of order of the stratum corneum lipids. A lamellar cream with a structure similar to that of the stratum corneum lipids increases the degree of order of the alkyl chains of the skin lipid film (biomimetic principle), whereas a conventional w/o cream reduces this degree of order. Skin moisture increases after the use of the creams.     

Prediction and measurement of surfactant action upon human skin under realistic conditions

The lysosomal enzyme acid phosphatase has been characterized and quantified in tapestrip biopsies of human stratum corneum by means of a sensitive spectrofluorometric procedure. When the stratum corneum of panellists was exposed to dilute solutions of various surfactants under realistic exposure conditions, the changes observed in stratum corneum acid phosphatase specific activity have been found to correlate very closely with the visual, macroscopic changes such as dryness and flakiness, that are elicited in skin as a result of surfactants. This method monitors denaturation of stratum corneum proteins, which is an important feature of skin surfactant interactions, and serves as an effective, non-invasive predictive tool for skin irritancy and mildness of surfactants.
Prevention et mesure de l'action des tensio-actifs sur la peau humaine dans des conditions conformes a la réalité     

Vol. 42, No. 1, pp.16-21, 2008Decrease in the skin transparency induced by protein carbonylation in the stratum corneum

It has been reported in recent years that the carbonyl modification of protein plays a part in various diseases. The existence of the protein carbonylation in the stratum corneum also came to be known in the last few years, but the effect on the properties of the stratum corneum including the skin appearance was not clarified. In this study, we examined the influence of protein carbonylation in the stratum corneum to provide helpful information for skin care products focusing on transparency of the stratum corneum. Firstly, we developed a method to assess the protein carbonylation level numerically by the image analysis of tape-stripped stratum corneum reacted with a fluorescent hydrazide. The level of stratum corneum carbonylation of the sun-exposed site (face) was higher than that of unexposed site (upper arm), and the surface part of the stratum corneum showed a higher level of carbonylation compared with the deeper layer. Stratum corneum carbonylation was induced by in vitro UV irradiation. In addition, it was shown that the skin transparency score was significantly low in the woman with high level of protein carbonylation in the stratum corneum of the cheek. An experimentally carbonylated stratum corneum sheet in vitro became opaque. Among the amino acids investigated, L-lysine was the most effective to prevent carbonylation of the stratum corneum ex vivo . Moreover, L-lysine inhibited the decrease in the skin transparency caused by experimental carbonylation of the stratum corneum in the human skin. These results suggest that preventing the carbonylation of the stratum corneum due to adverse effects from the environment by l-lysine could improve the skin transparency.
Keywords: stratum corneum, protein carbonylation, appearance, skin transparency, l-lysine, amino acids, fluorescent hydrazide, tape-stripping     

Predicting skin penetration of actives from complex cosmetic formulations: an evaluation of inter formulation and inter active effects during formulation optimization for transdermal delivery

Twenty products, containing a radiolabelled form of each active in typical cosmetic formulations, were made and applied to female human epidermal membranes mounted in Franz diffusion cells for 48 h under ‘in use’ conditions. The products consisted of combinations of five formulations (a hydro‐alcoholic gel, an oil in water emulsion, a water in oil emulsion, a microemulsion and an oil) with four model drug actives (testosterone, hydrocortisone, 5‐fluorouracil and ketoconazole). Steady‐state flux appeared to be reached by 8 h and maintained for all products, other than for the microemulsions, consistent with the actives being present in the residual formulation on the skin at saturation. The recovery for each active at the end of the 48‐h study (from a series of stratum corneum tape strips, the remaining skin, cumulative amount penetrating into the receptor solution, product washed from the skin and on the donor chamber cap) ranged from 86.5% to 100.6%. The rank order of the fluxes for the actives from the hydro‐alcoholic gel is consistent with the known active molecular size and polarity determinants for maximum epidermal flux. Actives with similar steady‐state (maximum) fluxes from a range of formulations had retention in the stratum corneum and similar transport rate constants through the stratum corneum. The microemulsion formulation significantly enhanced both the stratum corneum steady‐state flux and transport rate constant for 5‐fluorouracil, hydrocortisone and testosterone. The penetration flux of each active could be related to its size and polarity and appeared maximal when the actives in the different cosmetic formulations applied to the skin under ‘in use’ conditions were likely to remain in the residual product on the skin as a saturated solution after solvent evaporation. Enhanced penetration fluxes can be achieved by formulation selection and an appropriate choice/mix of emollients/adjuvants. The principles described here provide a framework for understanding the delivery of cosmetic ingredients from various formulations.     

In vivo evaluation in man by two noninvasive methods of the stratum corneum barrier function after physical and chemical modifications

This study investigated the effect of different treatments on skin permeability, in vivo in man, by two noninvasive methods: transepidermal water loss (TEWL) determination measured with an evaporimeter, and Laser Doppler velocimetry (LDV) to measure the lag time before the vasodilatation induced by application of methyl and hexyl nicotinates.
Different treatments were performed on forearms of volunteers: 1. removal of the stratum corneum by stripping, 2. occlusion and hydration of the stratum corneum, 3. application of three surfactants in aqueous solution (Tween 60, sodium dodecyl sulphate and cetyl trimethylammonium bromide).
Increase in TEWL and decrease in lag time before the vasodilating effects of nicotinates measured with LDV after all treatments confirmed the modifications in skin permeability. The variations observed were more or less significant depending on the treatment, the investigative method, and the molecule used for the penetration study. With methyl (hydrophilic) nicotinate, the more TEWL increased, the more lag time decreased. A significant decrease in lag time after hexyl (lipophilic) nicotinate application was observed when there was a very high increase in TEWL. The lipophilic nature of the stratum corneum barrier was confirmed in vivo. Use of these two complementary methods, TEWL and LDV, allows the evaluation in vivo of the effect of different treatments on skin permeability in man.     

First skin-physiological tests in weightlessness in the ISS space station

Citation: IFSCC Magazine , 11 (2008) (3) 231–238
A prolonged stay in weightlessness induces several medical alterations of the human body and also results in impairment of the skin. The stratum corneum, epidermal barrier as well as other skin compartments are affected in terms of their susceptibility to dryness, desquamation and pruritus. This can lead, for example, to wound healing disorders. Skin physiological tests were performed on the skin of an astronaut during the ASTROLAB-Mission within the Skin Care program initiated by the ESA. The skin was analyzed before, partly during and after the mission. In addition, the tests were repeated after 1 year. During the mission a control skin area was treated with a skincare product. The results showed corneal disturbance caused by environmental conditions, suboptimal skin cleansing and skin care. The observed effects were minimized by application of a skincare product. Measurements of the epidermis showed an accelerated rate of epidermal keratinization; skin elasticity was reduced distinctly and the sonographic examination showed a disaggregation of the cutis with hypoechoic areas. Additional measurements performed a year after the mission indicate that the verified alterations, which in a broader sense seem similar to skin ageing and appear as a time lapse process in weightlessness, are reversible. Further testing of the preventive efficacy of anti-ageing products from a cosmetic point of view would appear to be an appropriate objective for prospective long-term space missions.
Keywords:  Weightlessness, skin changes, hydration, TEWL, SELS (Visioscan^®), elasticity, US-B-scan     

What are meters measuring?

There is increasing pressure on manufacturers of cosmetic products to provide data to support claims. Data are available from many sources including historical (published literature), laboratory data, cell culture experiments and human studies. Undoubtedly, human studies are the most reliable, and there are a wide range of tests available. Many meters have been developed for measuring different aspects of skin physiology but an understanding of these devices is essential, otherwise the data generated is of little value. There is some confusion as to what exactly some meters measure, an example of which is transepidermal water loss (TEWL) and water content (hydration) of the stratum corneum. Measurement of TEWL is used mainly to support claims that a product may, in the short or long term, improve or repair the barrier function of skin. It is not an indicator of hydration of the stratum corneum. One way to measure hydration is to look for the changes in electrical properties of the stratum corneum that the increased water content produces, i.e. measure capacitance or conductance. It is important that we do not loose sight of the fact that meters may measure something that is imperceptible to the consumer or has no meaning to them. Reliance only on devices that give numbers may lead to problems. An example of a study where three facial cosmetic products were subjected to perceptual tests and to a standard volunteer test for moisturization will be discussed. The relationship between any measured parameter, and what it means to the consumer, needs to be understood. A moisturization claim may be technically supported by a study using a device such as the Corneometer. However, a 20% increase in water content almost certainly does not represent a 20% better moisturization as far as the consumer is concerned. The way forward is to relate the two approaches to product testing during product development. Hopefully, this will allow the product development process to be more systematic.     

Eucalyptus increases ceramide levels in keratinocytes and improves stratum corneum function

The objectives of this study were to identify a plant extract that would improve stratum corneum functions and to elucidate the mechanism(s) involved. Based on the information that stratum corneum functions depend on the level of ceramide in the stratum corneum, we identified a Eucalyptus extract that was able to increase the level of ceramide in human keratinocytes in culture and in human stratum corneum and that improves the stratum corneum water holding and barrier functions. Addition of the Eucalyptus extract to human keratinocytes in culture increased the level of ceramide in a dose-dependent manner and also increased the biosynthesis of ceramide, glucosylceramide and sphingomyelin. Topical application of the Eucalyptus extract on the dry skin of human subjects induced by acetone and diethylether treatment resulted in a significant increase in ceramide level in the stratum corneum, a significant improvement in its water-holding function and an improvement in its barrier function. The addition of macrocarpal A, one of the main components of the Eucalyptus extract, to human keratinocytes in culture increased the level of ceramide and the mRNA expression of serine palmitoyltransferase, acid sphingomyelinase, neutral sphingomyelinase, glucosylceramide synthase and glucocerebrosidase in a dose-dependent manner. Our results indicate that the increased content of ceramides in the stratum corneum may underlie the therapeutic effect of the Eucalyptus extract. Our results also indicate the possibility that macrocarpal A is the key component that stimulates the synthesis of ceramide in the stratum corneum.     

Use of infrared spectroscopy for in vivo measurement of the stratum corneum moisturization after application of costmetic preparations

In this study the moisturization of the stratum corneum was assessed using a non-invasive and non-destructive in vivo method, i.e., Fourier Transform Infra Red spectroscopy. First, the values of absorption band integrations were recorded for the non-treated skin. Next, the results after application of various cosmetic preparations were reported and correlated with corneometric findings.     

Skin lipid organization,composition and barrier function

Citation: IFSCC Magazine, 10 (2007) (4) 297–307 The primary function of the skin is to act as a barrier against unwanted influences from the environment and to protect the body from water loss. The barrier function of the skin is located in the superficial layer of the skin, the stratum corneum. The stratum corneum consists of dead cells filled with keratin and water, the corneocytes, embedded in lipid regions. As the lipid regions are the only continuous structure in the stratum corneum, they are considered to be very important for the skin barrier function. The main lipid classes are ceramides, cholesterol and free fatty acids. In this paper the lipid organization in human stratum corneum is reviewed. In addition, the role the various lipid classes play in lipid organization is discussed using mixtures prepared from either native human ceramides or synthetic ceramides. Finally, a model is described which allows study of the relation between lipid composition, organization and barrier function. This model is referred to as the stratum corneum substitute. Keywords: ceramides, FTIR, lipid organization, stratum corneum, X‐ray diffraction     

Human skin equivalents are an excellent tool to study the effect of moisturizers on the water distribution in the stratum corneum

In this study, the mode of action of moisturizers on the level of water in the stratum corneum was studied using cryo‐scanning electron microscopy. As model for dry skin, we used human skin equivalents (HSEs) generated at 93% or 60% relative humidity (RH). During the generation of the HSEs, the moisturizers were applied during a period of maximal 2 weeks. In HSEs generated under normal culture conditions (93% RH), application of 10% glycerol or 5% urea formulations resulted in increased water levels. Whereas the 5% urea formulations resulted mainly in the formation of intercellular water domains, after 10% glycerol both swelling of corneocytes and formation of intercellular water domains were noticed. A reduction in RH to 60% during treatment reduced the stratum corneum water levels drastically. Treatment with the non‐occlusive lipophilic moisturizer isopropyl isostearate resulted in increased water level in the central part of the stratum corneum compared with the untreated control. Our results show that HSEs can be used as a model to study the water distribution.     

Skin barrier structure, function and formation - learning from cryo-electron microscopy of vitreous, fully hydrated native human epidermis

The hydration level of the stratum corneum largely depends on the physical state and molecular organization of the stratum corneum intercellular lipid matrix. A better understanding of stratum corneum lipid organization may thus aid the development of more rational cosmetic formulations. Several experimental and theoretical problems of a fundamental character remain, however, unresolved. These are, e.g. that precise quantitative skin barrier compositional data are difficult to obtain and that in vitro experimental skin barrier models usually are of limited value because of the prevailing non-equilibrium conditions in vivo. However, new experimental methods have recently been developed, which may help to overcome some of these limitations. These are, e.g. direct electrospray ionization-mass spectrometry (ESI-MS) of intact long-chain skin ceramides and direct high-resolution cryo-transmission electron microscopy (cryo-TEM) of vitreous sections of native, fully hydrated epidermis. Here, we show that cryo-transmission electron micrographs of vitreous normal human skin often dramatically differ from those obtained by conventional electron microscopy of resin-embedded skin. Our epidermal cryo-TEM data are subsequently discussed in relation to central problems of present conceptions of skin barrier structure, function and formation.     

Surfactants and the skin

The skin surface is the interface between us, the organism, and the outside world. When we clean the skin we remove not only the bacteria, dirt and grease which have accumulated, but also part of our natural barrier - the stratum corneum. Corneocytes, both singly and in clumps, are released from the skin surface by the action of detergents and mechanical stimulation. So too are the lipids and proteins which make up the intercorneocyte region of the stratum corneum. The analysis of the types and amounts of materials released by a standard scrub procedure may prove useful in the selection of surfactants with particular properties. Changes in the physical properties of the skin occur after washing. For example, changes in skin surface pH and transepidermal water loss (a sensitive index of barrier function) are easily demonstrable. Excessive exposure to surfactants results in repeated damage to the stratum corneum which can in turn lead to an irritant dermatitis. Individual susceptibility to irritant dermatitis varies and this may be demonstrated using a simple patch test technique. This test is a way of potentially increasing the sensitivity of human based assays such as the soap chamber test by preselection of subjects. Alternatively it may be possible to use measurements of function such as transepidermal water loss or laser Doppler blood flow as an index of damage rather than conventional cutaneous irritancy. These approaches may help in the search for the ideal of a non-irritant cleanser.     

Control of melanosome transfer by promoting shrinkage or expansion of melanocyte dendrites

Coenzyme Q₁₀ is an endogenous antioxidant found in the skin along with vitamins A, C and E. Coenzyme Q₁₀ is used increasingly in cosmetic products and is advertised as a skin energizer, protector against skin aging, skin repairer and an anti-wrinkling agent. As the outermost layer of skin, the stratum corneum is the interface between the body and the environment and requires antioxidants to protect it and the epidermis and dermis below it. Nutrient levels in the stratum corneum correlate with those in the skin. Two forms of coenzyme Q₁₀ (pure coenzyme Q₁₀ and a yeast-based coenzyme Q₁₀) were investigated in a commercial vehicle. Two groups of subjects were tested aged 21–29 and 51–70, respectively. Coenzyme Q₁₀ absorption in the stratum corneum was determined after a 1-h application and ethanol extraction. Significantly more yeast coenzyme Q₁₀ was absorbed than the pure coenzyme Q₁₀ and the middle-aged subjects absorbed about twice as much coenzyme Q₁₀ as did the younger subjects. Skin antioxidants were significantly increased by yeast coenzyme Q₁₀ but not by pure coenzyme Q₁₀. Peroxides declined in the stratum corneum after twice daily application of coenzyme Q₁₀ with both forms but the decrease was greater with the yeast form. The older subjects had significantly higher baseline levels of lipid peroxides than did the younger group, indicating an increase in skin oxidative damage with age. The yeast coenzyme Q₁₀ is the superior form of coenzyme Q₁₀ for human skin application.     

Non-invasive assessment of stratum corneum structure and function

Methods for the study of the stratum corneum in situ are described and their application to clinical problems and cosmetic science are discussed. In vivo measurements of the thickness of skin and the components of skin can be made using high frequency pulsed ultrasound. Improved resolution of the device should allow measurement of epidermal thickness, and even that of the stratum corneum, which may vary with hydration. The protective ability of the stratum corneum can be estimated in a number of ways, the most familiar technique being transepidermal water loss measurements. Mechanical properties of the stratum corneum have been widely investigated in vivo by numerous researchers. A recent technique devised by us to deform the stratum corneum using an extendable metal frame has been used on patients with ichthyotic disorders. The deformation or compliance of the skin surface has been measured using profilometric methods, and compared to normal individuals. The results appear to be in agreement with the loss of flexural ability experienced by ichthyotic patients. Other mechanical methods more usually involve the measurement of the forces generated by skin while undergoing extension. Three techniques are described which have been used to investigate hydrational change with emollient application. Finally, the phenomenon of desquamation is discussed and methods presented for its evaluation. Passive collection of corneocytes using chambers is useful for estimation of the rates of desquamation, but are laborious and inconvenient. Forced desquamation using the desquamator enables rapid controlled harvesting of corneocytes. In addition to this, the dansyl chloride fluorescence technique has been adopted for estimation of stratum corneum kinetics using visual comparison and fluorimetric techniques. These techniques require further refinement and validation, but the tests available now are nonetheless important in understanding the biology and pharmacology of the stratum corneum.     

A liquid crystal application in skin care cosmetics

Intercellular lipids of the stratum corneum contribute threefold to the maintenance of a healthy skin: by hydration, cell adhesion, and reduction of transepidermal water loss. All of these functions can be attributed to the self-organizing property of the amphiphilic molecules of the stratum corneum lipids. A new type of skin care product called Lamellar Gel was developed, which contains a (synthesized) pseudo-ceramide. Its structure is similar to that of ceramide found among the stratum corneum lipids, which allows it to control intramolecular interactions. Compared to regular emulsions the Lamellar Gel demonstrated better skin care characteristics regarding permeability, skin hydration, and skin occlusion. This was attributed to the fact that it formed the same self-organizing structure as natural stratum corneum lipids, hence showing a high affinity to the skin. A high moisturizing effect was observed as the Lamellar Gel combines the benefits of both O/W and W/O emulsions: it provides the same initial hydration as an O/W emulsion and at the same time the same occlusivity as a W/O emulsion. Transepidermal water loss increases under dry environmental conditions. This especially affects the skin around the eyes, where the skin is very thin, and wrinkles are very easily formed. Treatment with the Lamellar Gel recovered these wrinkles promptly and hydrated the stratum corneum for a long time.     

J. Cosmet. Sci., 59, 217–224 (May/June 2008) In vivo spectrophotometric evaluation of skin barrier recovery after topical application of soybean phytosterols

The skin's uppermost thin layer, stratum corneum, plays a crucial role in protecting the body against unwanted influences from the environment. Disruption of the stratum corneum, by tape stripping or chemical injury, results in epidermal recovery of the skin barrier. Soy phytosterols are widely used in the cosmetic field as active ingredients in creams and lipsticks. Furthermore, they deserve an important place among nutracosmeceuticals; in fact, after their absorption from the diet they are transferred from the plasma to the skin, playing an important role in the constitution of skin surface lipids. The aim of the present work was to study the effect of the topical application of soybean phytosterols on skin barrier recovery in human volunteers using the extent of methyl nicotinate (MN)-induced erythema in damaged skin as a parameter to evaluate the rate of stratum corneum recovery. MN was chosen as an erythematogenous substance for its capability to cause an erythema whose intensity and duration are proportional to the quantity of the substance that has entered the living epidermis over time. MN-induced erythema was monitored using reflectance spectrophotometry as a non-invasive instrumental technique. The results show clearly that soy phytosterols exert positive results on skin repair; in fact, 3 days after tape stripping, the sites treated with a formulation containing phytosterols showed an appreciable recovery of barrier function compared to those treated with a vehicle control without soy phytosterols.     

Exfoliation for sensitive skin with neutralized salicylic acid?

Citation: IFSCC Magazine, 11 (2008) (2) 115–119 Abstract: Hydroxy acids enjoy tremendous interest in cosmetology thanks to their skin anti‐ageing and water barrier enhancing activities. One of their actions is to promote the natural stratum corneum (stratum corneum) desquamatory process. However, their use is limited due to an inherent pH‐related irritancy potential which is even more exacerbated on sensitive skin. Clearly there is an opportunity for improvement. In this research we evaluated in humans the efficacy of salicylic acid, and its salts, as a corneodesmolytic agent using the dihydroxyacetone method and measuring the reduction in skin staining with treatment over time using a chromameter. Salicylic acid at 2% in a preparation of pH 3.12 significantly increased exfoliation by 10.9% compared with placebo (P < 0.05), confirming its desquamatory enhancing properties. Then the effect of vehicle cream pH on salicylic acid activity was studied. Salicylic acid at close to neutral pH (mostly in its neutralized form as salicylate, pH 6.50) exerted a corneodesmolytic activity as good as that of salicylic acid in an acidic vehicle (pH 3.12) after only two days of application. Furthermore, the performance of glycolic acid and salicylic acid salts as exfoliants were compared at pH 6.50. When these two hydroxyl acids were formulated at the same molar level in a cosmetic base (14.47mmol L^‐1), the salicylic acid preparation gave an 8.2% increase in stratum corneum desquamation compared with the glycolic acid preparation (P < 0.05). The corneodesmolytic effects were confirmed using a tape‐stripping assay combined with a quantitative protein assay. Neutralized salicylic acid was found to enhance the removal of stratum corneum proteins significantly more than the vehicle after 25 sequential tape strippings (14%; P < 0.05). Finally, salicylic acid had no significant influence on skin water barrier properties after 22 days of treatment. In the second phase of this research we assessed the suitability of neutralized salicylic acid as an ingredient for sensitive skin. A stinging test was performed according to the Frosch & Kligman method to evaluate the influence of the formulation base‐pH on stinging potential. Salicylic acid formulated at pH 6.50 induced no stinging sensation (score 0) in contrast to salicylic acid at pH 3.12 (score 19; P < 0.05). In addition, a clinical study was conducted to assess the erythema induced on volunteers’ cheeks after a single application of a neutralized salicylic acid (1%) formulation compared with placebo. Visual redness was assessed by a dermatologist and then measured with a Mexameter. No significant differences were observed. Moreover, half of the panel had sensitive skin and no correlation could be established between redness and/or abnormal sensation and sensitive skin. In conclusion, neutralized salicylic acid at a 1% concentration is a suitable exfoliant agent for subjects with sensitive skin. Keywords: exfoliation, hydroxy acids, Salicylic acid, stratum corneum Paper presented at the IFSCC Conference 2007, Amsterdam, The Netherlands.