Perianal dermatitis of the newborn

**Definition:** Perianal dermatitis of the newborn presents with perianal erythema during the first week of life, which in more severe forms may progress to oedema and superficial erosion of perianal skin. Although it usually occurs alone, perianal dermatitis may sometimes be associated with primary irritant napkin dermatitis. It is commoner in infants receiving cow's milk formulations than in breast-fed infants; it is assumed that it represents an irritant response to faecal constituents.