Diaper rash is an irritation (reddening, sometimes with small pimple-like dots) of the skin normally covered by the diaper. This rash appears most obvious on the lower abdomen, genitals, around the anus and in the folds of skin in the groin. The buttocks are less often involved. Most babies get diaper rash sometime in the first year of life.
Anything that irritates and has prolonged contact with the skin can cause diaper rash. Urine and stool are both irritating to the skin and if the diaper is left on too long, diaper rash will occur. Allergies to plastic pants, disposable diapers, detergents and fabric softeners (if you use cloth diapers), lotions, and powders can also cause diaper rash, but are infrequent causes. Diaper rash is less common in breastfed infants and more common in those who are taking solid foods or who have diarrhea.