Dandruff (Seborrhoeic Dermatitis) — Causes, Malassezia, Shampoos & Treatment Guide — Symptoms, Causes & Treatment | MyMedicPlus

Dandruff (pityriasis capitis) is a chronic, non-inflammatory condition of the scalp characterised by excessive flaking of scalp skin cells (keratinocytes), causing visible white or grey flakes on hair and clothing, often accompanied by scalp itching. It is one of the most common scalp conditions, affecting approximately 50% of adults worldwide. Dandruff is closely related to seborrhoeic dermatitis (SD) — a chronic inflammatory skin condition affecting the scalp, face (eyebrows, nasolabial folds, beard), chest, and other sebaceous gland-rich areas — which represents a more severe manifestation on a spectrum. The yeast Malassezia globosa and M. restricta (lipophilic yeasts naturally present on human skin) play a central role in both dandruff and seborrhoeic dermatitis by metabolising sebum to oleic acid, which penetrates the stratum corneum and triggers an inflammatory response in susceptible individuals.

Malassezia yeast overgrowth: the primary pathogenic mechanism — Malassezia metabolises sebum triglycerides (using lipase enzymes) to free fatty acids, including oleic acid, which disrupts the scalp epidermal barrier and triggers accelerated keratinocyte turnover (normal scalp turnover: 28 days; dandruff: 7-14 days). Excess sebum production (seborrhoea): increased androgens (puberty, testosterone) stimulate sebaceous glands; sebum provides substrate for Malassezia growth. Genetic predisposition: individual sensitivity to Malassezia lipase products determines susceptibility. Risk factors: male sex (higher sebum production, higher prevalence); adolescence and early adulthood; stress (exacerbates sebum production and immune dysregulation); cold, dry weather; certain neurological conditions (Parkinson's disease, epilepsy) — notably high seborrhoeic dermatitis prevalence; HIV/AIDS (severe, treatment-resistant seborrhoeic dermatitis is an early manifestation); facial hair (provides Malassezia-rich microenvironment); use of certain hair products (pomades, oils — promote Malassezia growth).

Dandruff (mild): white or grey dry flakes visible on the scalp, hair, and dark clothing; scalp itching (pruritus) — often worse in winter; scalp may appear oily. Seborrhoeic dermatitis (moderate-severe): yellowish, greasy, adherent scales on the scalp; erythema (redness) of the scalp — may extend to the hairline, behind the ears, and into the external ear canal; facial involvement — greasy scales on the eyebrows, nasolabial folds, and beard; blepharitis (eyelid scaling and redness); chest and axillary involvement in severe cases. Chronic course with flares (stress, illness, seasonal change) and remissions. Distinguishing from scalp psoriasis: psoriasis typically has well-defined silvery-white scales with a pinkish-red plaque border; often involves the nape of the neck, extending beyond the hairline; may be associated with nail changes and joint symptoms (psoriatic arthritis).

Dandruff and seborrhoeic dermatitis are primarily clinical diagnoses based on history and examination. No investigations are usually required for typical presentations. Dermatoscopy: magnified examination of the scalp may show yellowish adherent scale, periinfundibular erythema (redness around hair follicle openings) — helpful for differentiating from psoriasis. Scalp biopsy (histopathology): rarely needed; shows non-specific features of seborrhoeic dermatitis (focal parakeratosis, follicular plugging, spongiosis, perivascular lymphocytic infiltrate). Differential diagnosis: scalp psoriasis (well-demarcated plaques, silvery scales); tinea capitis (scalp ringworm — more common in children; broken-off hairs, kerion; confirmed by Wood's lamp and fungal culture — requires oral antifungal treatment); contact dermatitis (reaction to hair dye, shampoo); atopic eczema (scalp involvement possible, usually in context of widespread atopic disease).

Antifungal shampoos (first-line): ketoconazole 2% shampoo (Nizoral) — used 2-3 times weekly for 4 weeks, then once weekly for maintenance; most effective antifungal for dandruff/SD; available over-the-counter. Zinc pyrithione shampoos (Head and Shoulders, Selsun Blue with ZPT): antifungal and antibacterial; daily use; good for mild dandruff maintenance. Selenium sulphide 2.5% shampoo: antifungal and sebostatic (reduces sebum production); apply 2-3 times weekly; avoid contact with eyes or coloured hair. Salicylic acid and sulphur shampoos: keratolytic — dissolve and loosen thick scales, allowing antifungals to penetrate. Coal tar shampoos (Polytar, T/Gel): antifungal, antiproliferative, anti-inflammatory; slightly cosmetically unacceptable (odour, staining) but effective. Topical corticosteroids: for scalp seborrhoeic dermatitis with significant inflammation — betamethasone valerate 0.1% scalp application or clobetasol propionate scalp foam; use as short courses (2-4 weeks) to control flares. Ciclopirox olamine 1% shampoo/gel: broad-spectrum antifungal; effective for seborrhoeic dermatitis; often combined with corticosteroids. Facial seborrhoeic dermatitis: ketoconazole 2% cream; low-potency topical corticosteroids (hydrocortisone 1%) short-term; calcineurin inhibitors (tacrolimus 0.1% ointment, pimecrolimus 1% cream) as steroid-sparing alternatives. Severe/refractory cases: refer to dermatologist; consider oral itraconazole (200 mg daily for 1 week/month); phototherapy (narrow-band UVB).

Untreated dandruff is usually benign but chronic and distressing. Social and psychological impact: embarrassment, reduced self-confidence, social withdrawal, and anxiety are significant consequences of visible flaking, particularly when the scalp is severe. Seborrhoeic dermatitis without treatment can spread beyond the scalp to affect the face, eyebrows, nasolabial folds, beard, ears, and chest — significantly impacting appearance and quality of life. Chronic scratching can cause excoriation, secondary bacterial infection (folliculitis, impetigo), and scarring alopecia if follicular damage occurs. Seborrhoeic dermatitis in HIV/AIDS can be severe and widespread — a marker of immune deterioration; treatment may require systemic antifungals and HIV antiretroviral therapy. Dandruff may contribute to or exacerbate blepharitis (eyelid margin inflammation), causing chronic eye irritation.

Dandruff cannot be cured but can be effectively controlled with regular treatment. Use an antifungal shampoo (ketoconazole or zinc pyrithione) once or twice weekly as long-term maintenance — even when the scalp is clear — to prevent Malassezia overgrowth. Reduce scalp oiliness: wash hair regularly (every other day or daily if scalp is very oily); avoid heavy oils, pomades, or thick hair products that promote Malassezia growth. Manage stress: psychological stress exacerbates dandruff and seborrhoeic dermatitis — regular exercise, mindfulness, and adequate sleep help. Moderate sun exposure: UV light suppresses Malassezia growth — brief, daily outdoor sun exposure may improve scalp SD (but avoid sunburn and long-term UV damage risk). Avoid very hot water when washing hair — it stimulates sebum production. Switch shampoos regularly: alternating between two antifungal shampoos (e.g., ketoconazole and zinc pyrithione) prevents Malassezia adaptation.

Most mild dandruff can be managed with over-the-counter antifungal shampoos without seeing a doctor. See your GP or dermatologist if: dandruff is severe, widespread, or not improving after 4–6 weeks of regular antifungal shampoo use; there is significant scalp redness, thickened plaques, or extension beyond the hairline to the face, ears, or eyebrows (severe seborrhoeic dermatitis may need prescription-strength topical steroids); the scalp is intensely itchy, causing significant distress or sleep disturbance; or you are unsure whether the condition is dandruff, scalp psoriasis, or another skin condition — accurate diagnosis changes treatment. Patients with HIV, Parkinson's disease, or who are immunosuppressed should seek early treatment for seborrhoeic dermatitis as it tends to be more severe and refractory in these groups.