Seborrheic dermatitis is a common inflammatory disease of the skin characterized by scaly lesions usually on the scalp, hairline, and face. It appears as red, inflamed skin covered by greasy or dry scales that may be white, yellowish, or gray. It can effect the scalp, eyebrows, forehead, face, folds around the nose and ears, the chest, armpits (axilla), and groin. Dandruff and cradle cap are mild forms of seborrheic dermatitis that appear as fine white scales without inflammation.

The cause of seborrheic dermatitis is unclear, although it is has been linked to genetic or environmental factors. Pityrosporum ovale , a species of yeast normally found in hair follicles, has been proposed as one possible causative factor. A high fat diet and alcohol ingestion are thought to play some role. Other possible risk factors include:

• Stress and fatigue
• Weather extremes (e. g. hot, humid weather or cold, dry weather)
• Oily skin
• Infrequent shampoos
• Obesity
• Parkinson's disease
• acquired immunodeficiency syndrome (AIDS)
• Use of drying lotions that contain alcohol
• Other skin disorders (for example acne, rosacea, or psoriasis)

Mild forms of the disorder may be asymptomatic (without symptoms). Symptoms also disappear and reappear, and vary in intensity over time. When scaling is present, it may be accompanied by itching that can lead to secondary infection.

The diagnosis of seborrheic dermatitis is based on assessment of symptoms, accompanied by consideration of medical history.

Treatment consists of vigorous shampoos with preparations that assist with softening and removing the scaly accumulations. For mild cases, a non-prescription shampoo with selenium sulfide or zinc pyrithione may be used. For more severe problems, the doctor may prescribe shampoos containing coal tar or scalp creams containing cortisone. The antiseborrheic shampoo should be left on the scalp for approximately five minutes before rinsing out. Hydrocortisone cream may also be ordered for application to the affected areas on the face and body. Application of the hydrocortisone should be discontinued when the condition clears and restarted with recurrence.

This chronic (ever-present) condition may be characterized by long periods of inactivity. Symptoms in the acute phase can be controlled with appropriate treatment. The condition cannot be prevented; however, severity and frequency of flare-ups may be minimized with frequent shampoos, thorough drying of skin folds after bathing, and wearing of loose, ventilating clothing. Foods that appear to worsen the condition should be avoided.