Common skin abnormality involving local accumulation of pigment, also called a mole. The condition is in fact so common that it can hardly be considered abnormal. It is a small brown to black patch, consisting of a dense accumulation of skin pigment, on which a few hairs may grow. There are variants set deeper in the skin, which show through as blue. If a naevus increases in size, starts to itch, bleed or become ulcerated, a doctor should be consulted immediately as there is a possibility of melanoma. Inflammation of the genital region in babies, associated with wet nappies. The most important cause is bacterial conversion of urea in urine to ammonia; materials used to wash and disinfect nappies can also cause or sustain nappy rash. Factors that encourage the condition are frequent excretion of thin faeces, not changing nappies often enough, inadequate cleaning of the buttocks, an excessive ambient temperature and constricting plastic pants. The first signs are redness of the groin, spreading over the genitals, buttocks, thighs and lower abdomen, which develops into a partially wet, partially scaly condition. There is often the smell of ammonia. Complications can occur if Candida cells grow over the rash, causing candidiasis, and a chronic pattern of development. Treatment is by frequent nappy changes and careful cleaning of the soiled area of skin using water. Diarrhoea should be treated if it occurs. Nappies should be thoroughly rinsed to remove alkali. Modern nappy liners, which keep the buttocks dry for longer, are also useful. The skin disorder itself is best treated with zinc ointment.