The aetiopathogenesis of atopic dermatitis (AD) is complex and during recent years much has been learnt regarding the genetic predisposition to the development of this condition and how its interaction with the environment influences clinical manifestations. AD is not a simple condition. An inherited stratum corneum barrier defect, transepidermal water loss, early antigen exposure through the skin and over-hygienic care of the young child seem to be the major drivers in the manifestation of the disease. Many other, more specific, environmental factors may influence the clinical picture in individual patients; some of these have an allergic basis, while others do not. In this article, the terminology used in this issue of CME is explained, the evidence for the different aetiopathological factors is presented and the factors that worsen or improve AD are listed.