Hypohidrotic ectodermal dysplasia (HED) is one of a diverse group of disorders that affect the skin and skin derivatives (teeth, hair, nails, sweat glands, and sebaceous glands). Disturbances in other organ systems are common in these diseases. The hallmarks of HED are a deficiency or complete absence of sweat glands, malformed or missing teeth, and a generalized decrease in body hair.