The acidic character of skin’s outer surface was first described in 1892 by Heuss1 and years later by Schade and Marchionini2 as acid mantle, and its importance has been recognized as playing a crucial role in permeability barrier homeostasis, skin integrity/cohesion and immune function.3–5 Given the significance of an acidic skin pH for normal functioning and defenses, it is important that the skin is therefore able to resist acidic/alkaline aggression to some extent—i.e., has a buffering capacity.6 With age, however, the pH of skin increases and its ability to buffer this change in pH decreases,7 which results in impaired barrier homeostasis and skin integrity/cohesion, an increased likelihood for skin infection, and increased sensitivity/irritation to topically applied products.8
This paper briefly reviews the basic science of pH and buffering capacity and the deleterious effects of increased pH in mature skin. In more detail, the authors consider which components of the stratum corneum (SC) are likely responsible for buffering capacity in skin of all ages, and discuss physiologic changes in the SC that may contribute to the decreased buffering capacity detected in mature skin.
pH and Buffering Capacity
pH is a measure of the hydronium ion concentration in the skin. When dilute aqueous acid or alkaline solutions come into contact with healthy skin, the pH changes—although this is generally temporary and the original pH is rapidly restored via buffering. Recall that a buffer is a chemical system that can limit changes in pH when an acid or a base is added.