Irritant diaper dermatitis (IDD) is a common condition caused by the combination of wearing diapers, and incontinence of urine and faeces. The available evidence suggests that maceration of the stratum corneum by water increases susceptibility to frictional damage, and epidermal permeation of irritants. The most important irritants underlying IDD appear to be digestive enzymes persisting in faeces, particularly when these are activated by a high pH.