(See also Definition of Dermatitis.)
Despite the name, the composition and flow of sebum are usually normal. The pathogenesis of seborrheic dermatitis is unclear, but its activity has been linked to the number of Malassezia yeasts present on the skin. Seborrheic dermatitis occurs most often in infants, usually within the first 3 months of life, and in adults aged 30 to 70 years. The incidence and severity of disease seem to be affected by genetic factors, emotional or physical stress, and climate (usually worse in cold weather). SD may precede or be associated with psoriasis (called seborrhiasis). SD may be more common and more severe among patients with neurologic disorders (especially Parkinson disease) or HIV/AIDS. Very rarely, the dermatitis becomes generalized.
Symptoms of seborrheic dermatitis develop gradually, and the dermatitis is usually apparent only as dry flakes (dandruff) or greasy diffuse scaling of the scalp (dandruff) with variable pruritus. In severe disease, yellow-red scaling papules appear along the hairline, behind the ears, in the external auditory canals, on the eyebrows, in the axillae, on the bridge of the nose, in the nasolabial folds, and over the sternum. Marginal blepharitis with dry yellow crusts and conjunctival irritation may develop. SD does not cause hair loss.
Newborns may develop SD with a thick, yellow, crusted scalp lesion (cradle cap); fissuring and yellow scaling behind the ears; red facial papules; and stubborn diaper rash. Older children and adults may develop thick, tenacious, scaly plaques on the scalp that may measure 1 to 2 cm in diameter.
In adults with involvement of the scalp, zinc pyrithione, selenium sulfide, sulfur and salicylic acid, ketoconazole (2% and 1%), and tar shampoo (available over the counter) should be used daily or every other day until dandruff is controlled and twice/week thereafter. A corticosteroid lotion (eg, 0.01% fluocinolone acetonide solution, 0.025% triamcinolone acetonide lotion) can be rubbed into the scalp or other hairy areas twice daily until scaling and redness are controlled.
For seborrheic dermatitis (SD) of the postauricular areas, nasolabial folds, eyelid margins, and bridge of the nose, 1 to 2.5% hydrocortisone cream is rubbed in 2 or 3 times daily, decreasing to once a day when SD is controlled; hydrocortisone cream is the safest corticosteroid for the face because fluorinated corticosteroids may cause adverse effects (eg, telangiectasia, atrophy, perioral dermatitis). In some patients, 2% ketoconazole cream or other topical imidazoles applied twice daily for 1 to 2 weeks induce a remission that lasts for months. An imidazole or hydrocortisone can be used as first-line therapy; if necessary, they can be used simultaneously. Calcineurin inhibitors (pimecrolimus and tacrolimus) are also effective particularly when long-term use is necessary. For eyelid margin seborrhea, a dilution of 1 part baby shampoo to 9 parts water is applied with a cotton swab.
In infants, a baby shampoo is used daily, and 1 to 2.5% hydrocortisone cream or fluocinolone 0.01% oil can be used once to twice daily for redness and scaling on the scalp or face. Topical antifungals such as ketoconazole 2% cream or econazole 1% cream can also be helpful in severe cases. For thick lesions on the scalp of a young child, mineral oil, olive oil, or a corticosteroid gel or oil is applied at bedtime to affected areas and rubbed in with a toothbrush. The scalp is shampooed daily until the thick scale is gone.
In adults, seborrheic dermatitis causes dandruff and sometimes scaling around the eyebrows, nose, and external ear, behind the ears, in the axilla, and on the sternum.
Seborrheic dermatitis can cause a thick, yellow, crusted scalp lesion in newborns or thick, scaly scalp plaques in older children and adults.
Treatments can include medicated shampoos and topical corticosteroids.