Seborrheic Dermatitis

Definition/diagnostic criteria Seborrheic dermatitis (SD), also known as seborrheic eczema, is a chronic inflammatory skin condition characterised by a scaly rash. It primarily affects areas with a high concentration of sebaceous glands, including the face, scalp and chest. The rash is marked by red, sharply marginated macules or patches covered with greasy-looking yellowish scales​​​​​​. In individuals with skin of colour, SD may present with scaly, hypopigmented macules and patches.

Epidemiology Globally, SD affects 1-5% of the population, with a slightly increased incidence among African Americans (6.5%) and West Africans (2.9-6%). There is increased prevalence in immunocompromised individuals, where rates can reach 34-83%. It is more commonly seen in males, likely due to the influence of androgens on sebum production. While it can occur at any age, peak incidences are noted in infants, adolescents and young adults​​.

Diagnosis
Clinical features:

• SD is most commonly observed in patients aged 18 to 40, but can manifest at any age.
• It predominantly impacts areas rich in sebaceous glands, such as the scalp, behind the ears, face (especially medial eyebrows, glabella, and nasolabial folds), upper trunk, and various flexures.
• Itchiness varies among individuals and is not always a predominant symptom​​​​.

Investigations:

• Diagnosis of SD is generally clinical, based on the characteristic distribution and appearance of the rash.
• Fine scaling, often referred to as ‘dandruff’, aids in confirming the diagnosis.
• In cases of atypical presentation or lack of response to standard treatments, further investigations such as fungal cultures, skin biopsies, or blood tests for underlying conditions like HIV may be necessary​​​​.

Treatment
General measures:

• Treatment aims to improve the appearance of the visible rash and to alleviate itch and erythema.
• Over-the-counter treatments are recommended for mild cases.
• Regular use of antifungal medication and intermittent topical steroids form the cornerstone of treatment, with no clear evidence favouring one antifungal over another​​.

Specific management:

• Scalp: Removal of thick crusts or scales with agents like olive oil, followed by medicated shampoos containing ketoconazole or selenium sulfide. Topical steroids may be used intermittently to reduce itching​​.
• Face, ears, chest, and back: Maintenance of skin hygiene without soap, application of antifungal creams (e.g. ketoconazole, miconazole) and intermittent courses of low-potency steroids like 1% hydrocortisone cream. Topical calcineurin inhibitors may be used as an alternative to steroids​​.
• Severe cases: Oral antifungal medications, oral tetracyclines for their anti-inflammatory effects, oral isotretinoin and ultraviolet light treatment are considered, typically after specialist consultation​​.

Prognosis SD generally responds well to treatment, but it has a tendency to relapse, necessitating maintenance or intermittent therapy for long-term control​​.