Atopic dermatitis in skin of colour. Part 1: New discoveries in epidemiology and pathogenesis.

Atopic dermatitis (AD) is a global condition that has a rising prevalence in developing countries such as those within South-east Asia and Latin America. Recent research re-presents the condition as a heterogenous disease of distinct endotypes among different ethnic groups. Variation between ethnic groups in physiological measures such as transepidermal water loss, ceramide-to-cholesterol ratio, skin sensitivity, alongside pathological barrier and immune system dysfunction processes, may ultimately lead to the distinct phenotypes seen clinically. AD in patients of Caucasian ethnicities is typified by filaggrin dysfunction, more Th1 and less Th17 involvement, with less epidermal thickness compared to patients of Black or Asian ethnicities. AD in patients of Black ethnic groups is Th2/Th22-skewed, with robust IgE expression, and less Th1 and Th17 involvement than patients of Asian or Caucasian ethnicities. AD across South Asian and East Asian populations is characterised by Th17/Th22 upregulation. Differences also exist in how AD psychosocially impacts individuals of different ethnic groups.