pH‐induced alterations in stratum corneum properties

Abstract

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.

Skin pH: From Basic SciencE to Basic Skin Care

“…Soap-based cleansers are known to have a higher potential to irritate skin than syndets (77-82). Ananthapadmanabhan and colleagues (83) have demonstrated that high-pH solutions even in the absence of surfactants increase SC swelling and lipid rigidity. The higher pH of soap bars may be a contributing factor in the higher irritation potential of soap bars compared to syndet bars.…”

Friction and lubrication of human skin

“…70% (i.e., about 2.5 g water/g dry tissue) at 100% RH or when immersed in water [37,39]. A pronounced swelling is associated with water immersion [40] and a considerable reduction in the YoungÕs modulus. Tensile experiments show that values for this parameter decrease from %1 GPa at 50% RH [41] to a value of %3 MPa in water [42].…”

Efficacy of the combined use of a mild foaming cleanser and moisturizer for the care of infant skin

“…However, a decrease in the number of infants with higher TEWL indicated that this combination skin care could improve lower cutaneous barrier function. It is important to maintain the infant skin surface at a weakly acidic pH to allow the development of skin barrier function,15 but some reports have indicated that skin pH is transiently raised by cleansing with soap, liquid surfactants, or water 13. The skin surface pH on the face, buttocks, and the flexor of the arm was decreased in both the lotion group and in the cream group.…”

“…It is hard to produce a fine foam without the use of a sponge or towel, but the use of these can naturally harm fragile infant skin because of excessive rubbing. The benefits of a weakly acidic base for cleansers have been also reported 12,13. We have therefore designed a mild acidic cleanser with less surfactant, which could be used as a fine-textured foam through a dispenser.…”