Seborrheic dermatitis is a form of skin inflammation (dermatitis) that causes a red, oily, flaking skin rash in areas of the body where glands in the skin called sebaceous glands are most abundant — the scalp, face and groin. In infants, it primarily affects the scalp, where it is called cradle cap. The causes of seborrheic dermatitis are unclear, but yeast may be involved in some cases.
Although doctors recognize that seborrheic dermatitis occurs in skin areas that have many sebaceous glands, they still do not know exactly why it develops there. It is thought that a tiny yeast may play a role in seborrheic dermatitis. Seborrheic dermatitis is a common skin disorder that affects people who often have no other health problems.