Seborrhoeic Dermatitis
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Direct answer
Seborrhoeic dermatitis is a chronic, relapsing inflammatory dermatitis of sebum-rich and flexural sites — the scalp, nasolabial folds, eyebrows, glabella, ears, presternal area and body folds — presenting with greasy yellow scale on well-demarcated erythema. It is linked to an altered immune response to lipophilic Malassezia yeasts rather than to excess sebum itself. Dandruff is its mildest, scalp-limited form; cradle cap is the infantile variety. Treatment uses antifungal agents such as ketoconazole shampoo and cream, mild topical corticosteroids and topical calcineurin inhibitors, with long-term maintenance because the tendency is lifelong.
What you must remember
- Distribution: scalp and margin (dandruff to severe marginal dermatitis), glabella, nasolabial folds, eyebrows and lids (blepharitis), retro-auricular folds, external ears, presternum in a petaloid pattern, and axillary, inframammary and inguinal flexures.
- Morphology: sharply demarcated erythematous patches covered with yellowish, greasy scale; flexural lesions may be moist, fissured and secondarily colonised — a "sebopsoriasis" overlap with psoriasis is described.
- Infantile type: cradle cap — yellowish greasy crusts on the scalp of neonates — plus flexural involvement, superficially resembling napkin psoriasis; it settles with mild keratolytics and emollients and usually clears by the first year. Sudden severe, generalised seborrhoeic eruption with diarrhoea and failure to thrive in an infant is Leiner disease, linked in older descriptions to complement C5 dysfunction.
- Marker associations: marked or refractory seborrhoeic dermatitis is a well-known early mucocutaneous marker of HIV infection; it is also common in Parkinson disease, after stroke, with lithium therapy and in stress or cold, dry seasons.
- Aetiology: Malassezia (Pityrosporum) yeasts drive inflammation in a susceptible host; sebum production and neurogenic factors modify expression — the yeast is a commensal, so the disease is not classically contagious.
- Treatment: ketoconazole 2 per cent shampoo or cream, ciclopirox or selenium sulphide preparations; mild topical corticosteroids for short courses on the face and flexures; tacrolimus or pimecrolimus as steroid-sparing options; eyelid hygiene for blepharitis; maintenance once to twice weekly antifungal washing to prevent relapse.
- Course: chronic and recurring, improving in summer and with sun exposure; no scarring or permanent hair loss is expected from uncomplicated disease.
Common confusion
Scalp and flexural seborrhoeic dermatitis is repeatedly contrasted with psoriasis: seborrhoeic dermatitis shows diffuse, fine, greasy scale with relatively flat erythema involving the nasolabial and retro-auricular areas, whereas scalp psoriasis forms thick, discrete, well-marginated plaques with silvery micaceous scale extending beyond the hairline, often with nail pitting. The second trap is infantile seborrhoeic dermatitis versus atopic dermatitis — the seborrhoeic infant is a comfortable, non-itchy baby with early scalp onset and flexural scaling, while the atopic infant is over two months, irritable and pruritic with dry skin. Sudden severe disease in an adult should prompt HIV testing.
Exam-focused takeaway
NEET-PG uses this topic for association one-liners — seborrhoeic dermatitis in HIV and Parkinson disease are the classics — and for image-based diagnosis of greasy facial scale in the nasolabial folds. Expect dandruff as the mildest form, ketoconazole as the drug of choice, Malassezia as the organism, and the infantile versus atopic comparison in paediatric-framed stems. Leiner disease with the triad of erythroderma, diarrhoea and failure to thrive appears occasionally as a difficult single-correct option.
Frequently asked questions
Which organism is linked to seborrhoeic dermatitis?
Lipophilic Malassezia yeasts (formerly Pityrosporum ovale or Pityrosporum orbiculare); they are normal commensals, and disease reflects an abnormal inflammatory response to them, which is why antifungal therapy helps.
What is cradle cap?
Thick, yellowish, greasy crusts on the scalp of infants within the first weeks of life — the infantile form of seborrhoeic dermatitis — usually clearing with emollients, gentle keratolysis or mild antifungal shampoos.
Why is seborrhoeic dermatitis called a marker of HIV?
Severe, extensive, treatment-resistant seborrhoeic dermatitis appears at higher CD4 counts than opportunistic infections and is one of the earliest mucocutaneous markers of HIV infection; new severe disease warrants an HIV test.
What is the difference between dandruff and seborrhoeic dermatitis?
Dandruff is non-inflammatory flaking limited to the scalp, whereas seborrhoeic dermatitis adds visible erythema and extends to facial and flexural sebum-rich sites; both respond to antifungal shampoos.
Which treatment is first line?
Ketoconazole 2 per cent shampoo or cream (alternatives include ciclopirox and selenium sulphide), combined with short courses of a mild topical corticosteroid or a calcineurin inhibitor for inflamed facial and flexural disease.
What is sebopsoriasis?
An overlap syndrome with features of both psoriasis and seborrhoeic dermatitis — well-defined greasy plaques on the scalp, face, chest and flexures — often treated as seborrhoeic dermatitis but monitored for evolution to psoriasis.