Cleansing without compromise: the impact of cleansers on the skin barrier and the technology of mild cleansing

There is evidence that the "acid mantle" of the stratum corneum is important for both permeability barrier formation and cutaneous antimicrobial defense. The origin of the acidic pH of the stratum corneum remains conjectural, however. Both passive (e.g., eccrine/sebaceous secretions, proteolytic) and active (e.g., proton pumps) mechanisms have been proposed. We assessed here whether the free fatty acid pool, which is derived from phospholipase-mediated hydrolysis of phospholipids during cornification, contributes to stratum corneum acidification and function. Topical applications of two chemically unrelated secretory phospholipase sPLA2 inhibitors, bromphenacylbromide and 1-hexadecyl-3-trifluoroethylglycero-sn-2-phosphomethanol, for 3 d produced an increase in the pH of murine skin surface that was paralleled not only by a permeability barrier abnormality but also altered stratum corneum integrity (number of strippings required to break the barrier) and decreased stratum corneum cohesion (protein weight removed per stripping). Not only stratum corneum pH but also all of the functional abnormalities normalized when either palmitic, stearic, or linoleic acids were coapplied with the inhibitors. Moreover, exposure of intact murine stratum corneum to a neutral pH for as little as 3 h produced comparable abnormalities in stratum corneum integrity and cohesion, and further amplified the inhibitor-induced functional alterations. Furthermore, short-term applications of an acidic pH buffer to inhibitor-treated skin also reversed the abnormalities in stratum corneum integrity and cohesion, despite the ongoing decrease in free fatty acid levels. Finally, the secretory-phospholipase-inhibitor-induced alterations in integrity/cohesion were in accordance with premature dissolution of desmosomes, demonstrated both by electron microscopy and by reduced desmoglein 1 levels in the stratum corneum (shown by immunofluorescence staining and visualized by confocal microscopy). Together, these results demonstrate: (i) the importance of phospholipid-to-free-fatty-acid processing for normal stratum corneum acidification; and (ii) the potentially important role of this pathway not only for barrier homeostasis but also for the dual functions of stratum corneum integrity and cohesion.

Although it is important that dermatologists and the general population know the irritation potential of products marketed for dry skin used for body cleansing, this information is not usually available. To assess the irritative effect of different soaps and liquid cleansers recommended for sensitive skin. To study the correlation of the irritation effect of each substance with its pH and with the presence or absence of syndet in the product. Seventeen products marketed for dry skin and 12 common soaps used by the general population were studied. Fresh soap emulsions (8%) were applied to the volar side of the right forearm of 30 individuals with sensitive skin for 5 consecutive days using aluminum chambers. The appearance of irritation (erythema, scaling and fissures) was recorded, scored, and expressed in an Irritation index (IrIn). The pH of each solution was measured. Products with a low IrIn were White Dove (Dove, Lever Pond's, Toronto, Ontario, Canada), Dove Baby, Cetaphil (bar) (Cetaphil, Gulderma Lab., Forth Worth, TX, USA), Dove liquid cleanser for hands, Dove pink, and Aderma (Adenma, Pierre Fabre, Dermo-Cosmetique, Boulagne, France). Most corresponded to syndet products. Among the most used brand-name soap, Camay Classic (Camay, Procter & Gamble de Mexico, México, U.F.) had the lowest IrIn. Dove Baby was the only product with a neutral pH. A significant correlation between pH and the IrIn of cleansers was found (P < 0.006). Most products recommended for sensitive skin have a considerable irritation effect, which is related to the pH of the product. Better regulation of advertisement specifications including the pH level and type of cleanser contained is necessary for the majority of soaps and cleansers.

Skin-cleansing compositions based on alkyl carboxylates (soaps) have a higher irritation potential than those based on syndet surfactants such as alkyl isethionates or alkyl ether sulphates. Contributing factors include inherent differences in the irritation potential of soaps and syndet surfactants, pH-induced changes in surfactant solution chemistry, and the direct effects of pH on the physical properties of the stratum corneum (SC). Past work has not directly addressed the effect of solution pH on the SC itself and its potential role in cleanser-induced skin irritation. In the current work, alterations to SC properties induced by buffered pH solutions and two strongly ionizable surfactants, sodium dodecyl sulphate and sodium lauryl ether sulphate, at different pH values are measured. By utilizing optical coherence tomography (OCT) and infrared (IR) spectroscopy we have directly measured physical changes in SC proteins and lipids. Our results indicate that SC swelling, which reflects alterations to SC structural proteins, is increased significantly at pH 10, compared to pH 4 and 6.5. The transition temperature (T(m)) of SC lipids is found to increase at pH 10, compared to pH 4 and 6.5, suggesting a more rigid SC lipid matrix. Surfactants cause a further increase in swelling and lipid rigidity. Some aspects of what these results mean for SC physical properties as well as their implications to potential mechanisms of surfactant-induced skin irritation are discussed.