Several epidermal barrier functions, like skin barrier regeneration and antimicrobial response, are related to the acidic nature of the skin surface pH (ss-pH). However, the epidermal acidification is known to be fragile and it is commonly accepted that cosmetic products, especially soaps and skin cleansing products, can induce significant changes in ss-pH. As a consequence, epidermal barrier function and skin microflora are affected negatively. ss-pH even increases after a single washing procedure or after rinsing the skin with water alone. The skin pH recovery needs time up to several hours before it can reach the physiological level. For cosmetic-relevant skin conditions, skin disorders and specific consumer groups, maintaining of the acidic ss-pH is beneficial for epidermal physiology and cutaneous microflora. In this context, cleansing and skin care products with a pH level of 4.0-5.0 may be helpful. In addition, combining the acidic product pH level with the ideal mix of surfactants, thereby enhancing product compatibility and minimizing skin irritation and intolerance, is a major challenge for the future. Beyond innovative cleansing technology, further multifaceted cosmetic research is a prerequisite to get deeper knowledge on the interrelation of product pH level, surfactant composition and corneobiology.
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