Dandruff affects approximately 50% of the adult population worldwide, making it one of the most common scalp conditions. Despite its prevalence, many people don’t treat it effectively — usually because they don’t understand what causes it.

What Actually Causes Dandruff?

Dandruff is not caused by poor hygiene or a dry scalp (though it can coexist with dryness). The primary cause is an overgrowth of Malassezia globosa, a yeast that lives on all human scalps. When Malassezia metabolises scalp sebum, it produces oleic acid — which penetrates the scalp in susceptible individuals, triggering skin cell turnover to speed up dramatically. Normally skin cells take about a month to turn over; with dandruff, it happens in 2–7 days. The visible flakes are clumps of shed skin cells.

Medicated Shampoos: The Active Ingredients

Ketoconazole 2% (Nizoral) — the most clinically effective antifungal shampoo. Kills Malassezia, addressing the root cause. Use twice weekly initially; once weekly for maintenance. Available OTC. Zinc pyrithione (Head & Shoulders) — antifungal and antibacterial properties. Effective for mild to moderate dandruff. Can be used daily. Selenium sulphide (Selsun) — antifungal and reduces cell turnover rate. Effective but may temporarily discolour dyed or chemically treated hair. Leave on for 2–5 minutes before rinsing. Salicylic acid — keratolytic; dissolves and loosens the flakes. Good as part of a two-step approach (salicylic acid to remove flakes, antifungal to treat cause). Coal tar — slows skin cell turnover; most useful for scalp psoriasis. Has a distinctive smell.

How to Use Anti-Dandruff Shampoo Correctly

Most people rinse out shampoo far too quickly. For medicated shampoos to work, they need contact time with the scalp — apply, lather, then leave for 3–5 minutes before rinsing. Use 2–3 times per week. Rotating between two different active ingredients every few weeks can prevent resistance and maintain effectiveness.

Scalp Psoriasis

Scalp psoriasis produces silvery-white, thick plaques rather than the fine, loose flakes of dandruff. It extends beyond the hairline onto the forehead, ears and back of neck. Requires different treatment: coal tar shampoo, salicylic acid preparations, and prescription topical steroids. If you think you have scalp psoriasis rather than dandruff, see your GP.

Shop Dandruff Treatments and Medicated Shampoos at Chemist 2 Customer.