(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 and to the inflammatory reaction to them. 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). Seborrheic dermatitis may precede or be associated with psoriasis (called seborrhiasis or sebopsoriasis). Seborrheic dermatitis may be more common and more severe among patients with neurologic disorders (especially Parkinson disease), because of, for example, changes in the activity of sebaceous glands, or among those with HIV/AIDS, likely because of an imbalance of T-cell pro- and anti-inflammatory responses. 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, on the eyebrows, in the nasolabial folds, and over the sternum. Marginal blepharitis with dry yellow crusts and conjunctival irritation may develop. Seborrheic dermatitis does not cause hair loss.
Newborns may develop seborrheic dermatitis 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.
Diagnosis of seborrheic dermatitis is made by physical examination.
Seborrheic dermatitis of the scalp must be differentiated from other disorders:
Atopic dermatitis of the scalp: This disorder typically first manifests with fine, white, dry scaling rather than the greasy yellowish scale of seborrheic dermatitis.
Scalp psoriasis: The erythematous and scaly plaques are sharply demarcated.
Rosacea: When rosacea affects the face, it first manifests with erythema, papules, and papulopustules but not with scaling (however, patients can have both seborrheic dermatitis and rosacea).
Treatment of seborrheic dermatitis of the scalp should include shampooing at least twice a week, because less frequent shampooing enables proliferation of Malassezia. Antifungal shampoos (eg, ketoconazole 2% or 1%) are highly effective in controlling the dandruff of seborrheic dermatitis. Keratolytic shampoos (zinc pyrithione, selenium sulfide, or sulfur and salicylic acid) and tar shampoos (available over the counter in the US) used daily or every other day until dandruff is controlled and twice/week thereafter are also helpful. If antifungals and keratolytics fail to sufficiently relieve pruritus, topical corticosteroid solutions (eg, 0.01% fluocinolone acetonide solution) are used. Although the scalp is one of the areas least susceptible to the adverse effects of topical corticosteroids (eg, telangiectasia, atrophy, folliculitis, acne, striae distensae), adverse effects can occur with long-term use, so topical corticosteroids should be used only as needed. Because seborrheic dermatitis tends to be chronic and often recurs with cessation of treatment, long-term use of antifungal shampoos (eg, once or twice weekly) is often required. Seborrheic dermatitis in beard and eyebrow areas is treated similarly to seborrheic dermatitis of the scalp. However, beard and eyebrow areas are more prone to the adverse effects of topical corticosteroids. Thus, corticosteroids should be used less frequently, and lower potency corticosteroid solutions (eg, 0.025% triamcinolone) should be used when possible.
For seborrheic dermatitis in nonterminal hair-bearing areas (eg, nasolabial folds, postauricular areas, sternum), treatment is similar. However, creams (which are typically not acceptable in hair-bearing areas) are preferred to solutions. For milder cases, 2% ketoconazole cream or other topical imidazoles applied twice daily are often sufficient. If not, mild topical corticosteroids (1 to 2.5% hydrocortisone cream, 0.2% hydrocortisone valerate cream) are applied twice daily. Higher potency topical corticosteroids are typically not required and should only be used short-term, if at all, because of the susceptibility of facial skin to the adverse effects of corticosteroids (eg, telangiectasia, atrophy, folliculitis/acne, perioral dermatitis). Calcineurin inhibitors (pimecrolimus and tacrolimus) are also effective, particularly when long-term use is necessary and antifungals alone are not sufficiently effective.
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, for example, 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 on the scalp, around the eyebrows, nasolabial folds, nose, external auditory canal, behind the ears, 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 include topical antifungals, keratolytic and tar shampoos, and topical corticosteroids.