pH in Atopic Dermatitis.

Atopic dermatitis (synonym atopic eczema, AD) is a chronic inflammatory skin disorder essentially characterised by a red "itchy" skin rash. The condition is prevalent around the world, affecting 15-30% of children and 2-10% of adults [Odhiambo et al.: J Allergy Clin Immunol 2009;124:1251-1258.e23]. The pathophysiological mechanisms underpinning AD are complex, broadly involving skin barrier dysfunction, an altered immune response (affecting both the adaptive and innate immune systems) and an unfavourable environment (external stressors) [Werfel et al.: J Allergy Clin Immunol 2016;138:336-349]. Intriguingly at the centre of this maelstrom of events, linking them together, is a very basic skin property - skin pH. Skin pH is a central regulator of skin barrier homeostasis and an important innate defence mechanism. Moreover, recent evidence suggests that elevated pH can also drive altered immune responses placing it squarely in the centre of AD pathogenesis, but just how important is skin pH to the development of AD? In this chapter, the current evidence entangling skin pH in AD pathogenesis is reviewed.