Diaper dermatitis, primary irritant diaper dermatitis, napkin dermatitis Definition and EpidemiologyDiaper dermatitis is one of the most common inflammatory dermatoses in infants occurring within the napkin area. It develops in as many as 50% of all diaper-wearing children, with a peak incidence between the 9th and 12th months of life. Secondary infection with Candida albicans is common and occurs in up to 50%. The great majority of cases are self-limiting and moderate in severity, and only in 6% of cases is diaper dermatitis severe and recurrent. Etiology and PathophysiologyThe pathophysiology of diaper dermatitis is due to a multitude of factors. It is now generally accepted that the most important irritants are feces-derived digestive enzymes, especially trypsin and lipase. The assumption of an irritant effect of digestive enzymes is based on the observation that overhydration of the skin is caused by prolonged contact with a wet napkin, which subsequently results in maceration of the skin. In addition, abrasive damage attributable to friction is the cause of a decreased barrier function favoring secondary irritants and infection.The intestinal tract of breast-fed children is less heavily colonized by urease-producing organisms such as enterobacteria. Urease degrades urea to ammonia and increases the alkalinity. Since the pH alkalinity in the feces of cow milk-fed infants is higher than in that of breast -fed children and the activity of such digestive enzymes as trypsin and lipase is related to increasing pH, breast-fed infants develop a diaper rash less frequently.Secondary infection with Candida albicans or various gram-positive bacteria (e.g. Staphylococcus aureus) is common and may aggravate the dermatitis. In approximately 50% of cases Candida albicans, mainly derived from the gastrointestinal tract, and less frequently bacteria are involved in the pathologic process. In addition, the warm, moist environment created by the diaper promotes the growth of these organisms.