Definition and Epidemiology

Seborrheic dermatitis is a chronic, common dermatosis that occurs across the life span. It is characterized by greasy, slightly erythematous scaling that occurs in areas with the highest concentration of sweat glands or sebaceous glands, including the scalp, face, and postauricular and intertriginous areas.^1,2 The disorder affects 1% to 5% of immunocompetent adults. Men tend to be affected more than women. Although the association is unclear, this disorder occurs in disproportionate numbers in patients with neurologic disorders (e.g., Parkinson disease, epilepsy, central nervous system disease or trauma) and may worsen with stress and fatigue.²

Pathophysiology

The cause of seborrheic dermatitis is unknown. Sebaceous gland secretion, the presence of Malassezia yeast, and the host immune response are thought to contribute to the condition.²

Clinical Presentation and Physical Examination

Seborrheic dermatitis is seen in both young and old patients. In infants, the most common presentation is yellow or brown scaling lesions on the scalp, which are called cradle cap. In adolescents and adults, another common presentation is dry, flaky scales on the scalp. This disorder is known as dandruff.^3,4

On the face and auricular area, seborrheic dermatitis is seen as greasy, erythematous, sharply marginated plaques. Polycyclic plaques are commonly seen on the sternal area. In the axillae and groin, the eruption manifests as more confluent plaques with fine scales and less well-defined borders. Lesions are usually asymptomatic, although pruritus is may be present.

Diagnostics and Differential Diagnosis

There are many differential diagnoses. More common diseases that can resemble seborrheic dermatitis include eczema, psoriasis, impetigo, dermatophytosis, tinea versicolor, intertriginous candidiasis, otitis externa, blepharitis, and systemic lupus erythematosus. Psoriasis is often described with more circumscribed, thicker plaques with a bright silvery hue. Seborrheic dermatitis can often overlap with psoriasis in a condition known as sebopsoriasis. Pityriasis versicolor is often less inflamed with more extension and flatter lesions. Atopic or contact dermatitis generally is accompanied by pruritus; patch testing may be needed. If the diagnosis is uncertain, a skin biopsy and immunofluorescence studies should be completed.

Less common diseases that can resemble seborrheic dermatitis include Langerhans cell histiocytosis, acrodermatitis enteropathica, pemphigus foliaceus, and glucagonoma syndrome. If these disorders are considered, there should be consultation with a dermatologist.

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