Research Summary:
Cleanser technology has evolved significantly from being focused solely on cleansing to also providing mildness and moisturizing benefits. It is well-established that harsh surfactants in cleansers can damage skin proteins and lipids, leading to after-wash tightness, dryness, barrier damage, irritation, and even itchiness. For cleansers to offer skincare benefits, they must first minimize surfactant-induced damage to skin proteins and lipids. Secondly, they should deposit and deliver beneficial agents such as occlusives, skin lipids, and humectants during the wash process to enhance skin hydration, as well as improve its mechanical and visual properties.
While all surfactants tend to interact with skin lipids, their interaction with skin proteins can vary significantly depending on the nature of their functional head group. In vitro, ex vivo, and in vivo studies have shown that surfactants which cause significant skin irritation tend to interact strongly with skin proteins. Based on these insights, several surfactants and surfactant mixtures have been identified as "less irritating" mild surfactants due to their reduced interactions with skin proteins. Surfactants that interact minimally with both skin lipids and proteins are particularly mild.
Another factor that can worsen surfactant-induced dryness and irritation is the pH level of the cleanser. Recent studies indicate that high pH solutions (pH 10), even in the absence of surfactants, can increase stratum corneum (SC) swelling and alter lipid rigidity. This suggests that cleansers with a neutral or acidic pH, closer to the skin's natural pH of 5.5, may be less damaging to the skin.
Mildness enhancers and moisturizing agents, such as lipids, occlusives, and humectants, help to reduce the damaging interactions between surfactants and skin proteins and lipids, thereby minimizing skin damage. Additionally, these agents play a restorative role by replenishing the skin lipids lost during the cleansing process. This review discusses the benefits of these agents and their roles in improving the overall health of the skin barrier.
KEYWORDS:
Amphoteric surfactants, anionic surfactants, dry skin, non-ionic surfactants, skin barrier damage, stratum corneum, syndet, surfactants, after-wash tightness.