Nappy rash

Irritant diaper dermatitis (IDD, also called a diaper or nappy rash) is a generic term applied to skin rash in the diaper (in British and Australian English "nappy") area that are caused by various skin disorders and/or irritants.

Generic irritant diaper dermatitis is characterized by joined patches of erythema and scaling mainly seen on the convex surfaces, with the skin folds spared.

Diaper dermatitis with secondary bacterial or fungal involvement tends to spread to concave surfaces (i.e. skin folds), as well as convex surfaces, and often exhibits a central red, beefy erythema with satellite pustules around the border.

It is usually considered a form of irritant contact dermatitis. The word "diaper" is in the name not because the diaper itself causes the rash but rather because the rash is associated with diaper use, being caused by the materials trapped by the diaper (usually feces). Allergic contact dermatitis has also been suggested, but there is little evidence for this cause. In adults with incontinence (fecal, urinary, or both), the rash is sometimes called incontinence-associated dermatitis (IAD).

The term diaper candidiasis is used when a fungal origin is identified. The distinction is important because the treatment is different (antifungals).