Atopic dermatitis is a multifactorial disease due to a combination of genetic and environmental factors. The pathophysiological mechanisms involved in AD are multiple: innate functional abnormality in the skin barrier partly linked to mutations of the filaggrin, a major structural protein of the skin; and genes involved in innate and adaptive immunity; Finally, the model of the hygiene theory has been clarified in recent years: environmental factors alter the diversity of skin and digestive microbiomes, and this diversity seems to play a major role in the development of atopy.