(See also Overview of Dermatitis.)
The cause is unknown, but the number of Malassezia yeasts, an organism normally present on the skin, plays some role. Seborrheic dermatitis occurs most often in infants, usually within the first 3 months of life, teens, and in those aged 30 to 70 years. The disorder is more common among men, often runs in families, and is worse in cold weather. Emotional or physical stress seems to worsen seborrheic dermatitis. A form of seborrheic dermatitis also occurs in as many as 85% of people with AIDS. Seborrheic dermatitis is also common among people with Parkinson disease.
Seborrheic dermatitis usually begins gradually, causing dry or greasy scaling of the scalp (dandruff), sometimes with itching but without hair loss. In more severe cases, yellowish to reddish scaly raised bumps appear along the hairline, behind the ears, in the ear canal, on the eyebrows, on the bridge of the nose, around the nose, on the chest, in the armpits, and on the upper back.
In infants younger than 1 month of age, seborrheic dermatitis may produce a thick, yellow, crusted scalp rash (cradle cap) and sometimes yellow scaling behind the ears and red pimples on the face. Frequently, a stubborn diaper rash accompanies the scalp rash.
Older children and adults may develop a thick, tenacious, scaly scalp rash with large flakes of skin.
In adults and older children, the scalp can be treated with a shampoo containing pyrithione zinc, selenium sulfide, salicylic acid and sulfur, or tar. The person usually uses the medicated shampoo daily or every other day until the dermatitis is controlled and then twice weekly. Ketoconazole cream (an antifungal drug) is often effective as well. Thick crusts and scales, if present, can be loosened with overnight application of corticosteroid lotions or salicylic acid under a shower cap.
Often, treatment must be continued for many weeks. If the dermatitis returns after the treatment is discontinued, treatment can be restarted. Topical corticosteroids are also used on the head and other affected areas. On the face, only mild corticosteroids, such as 1 to 2.5% hydrocortisone, should be used. Even mild corticosteroids must be used cautiously, because long-term use can thin the skin and cause other problems. Calcineurin inhibitors (pimecrolimus and tacrolimus) are also used, particularly for long-term therapy.
In infants, the scalp can be shampooed daily with mild baby shampoo, and 1 to 2.5% hydrocortisone cream or fluocinolone 0.01% oil can be rubbed into the scalp or face. Antifungal creams such as 2% ketoconazole or 1% econazole can be helpful in severe cases. For young children who have a thick scaly rash on the scalp, mineral oil, olive oil, or a corticosteroid gel or oil can be rubbed gently into the affected area with a soft toothbrush at bedtime.