Seborrhoeic Dermatitis (SD) is a very common chronic and/or relapsing inflammatory skin disorder presenting with a papulosquamous morphology in areas rich in sebaceous glands, particularly the scalp, face, and body folds.

Etiology

Yeast of the genus Malassezia has long been regarded as a main predisposing factor. Additional predisposing factors have been described, including sebaceous activity, host immunity (especially HIV infection), epidermal barrier integrity, skin microbiota, endocrine & neurologic factors, emotional stress and environmental influences.

Risk factors for the development of seborrheic dermatitis include:

• Age 
• Male sex 
• Increased sebaceous gland activity 
• Immunodeficiency, including:
• Lymphoma
• Renal transplantation
• HIV-AIDS
• Neurological and psychiatric disease, including:
• Parkinson disease
• Stroke
• Alzheimer dementia
• Major depression
• Autonomic dysfunction
• Exposure to drug treatment, including:
• Dopamine antagonists
• Immunosuppressants
• Psoralen/PUVA
• Lithium
• Low ambient humidity and/or low ambient temperature 

Clinical presentations

Seborrheic dermatitis is a clinical diagnosis based on the location and appearance of the lesions.

The incidence of SD notably peaks in three age groups, in infancy between 2 weeks and 12 months of age, during adolescence, and between age 30 and 60 years during adulthood.

In infants, SD presents as “cradle cap”—yellowish, greasy and crusty skin on the scalp—that is usually self-limited.

In adolescents and adults, SD is a chronic or relapsing condition, often presents as flaky, greasy yellowish scales with erythematous skin in seborrhoeic areas such as the scalp, face (eyebrows, nasolabial folds, above the upper lip), ears, retro-auricular area, the upper chest and trunks.

The face, scalp, and chest are the sites most commonly involved in Adult SD, with around 88%, 70%, and 27% of cases developing lesions in these areas, respectively.

In addition to skin inflammation, SD can be associated with pruritus.

Investigations

It is not necessary to routinely investigate seborrheic dermatitis

The following tests may be helpful in the differential diagnosis

• KOH examination of skin scrapings
• Swab for microscopy, culture, and sensitivities
• Histology and direct immunofluorescence
• HIV serology; VDRL
• Serum zinc levels
• ANA; ENA; ESR