Dandruff and seborrheic dermatitis in London: what actually works when shampoo isn't enough

Dandruff is the most searched, worst-treated scalp complaint in London. The vast majority of shoppers reach for a 'moisturising' or 'gentle' shampoo — and get worse. The vast majority of GPs prescribe hydrocortisone and it doesn't hold. The vast majority of dandruff shampoos are used incorrectly.

This guide is what a trichologist would tell you in a 45-minute consult: what is actually happening on your scalp, which actives to buy, how to use them, and when to escalate.

The Malassezia story

Every human scalp carries Malassezia — a lipophilic yeast that lives off sebum. In most people it lives quietly. In some (roughly half the adult population, more in men, more in central heating climates like London winters), the scalp mounts an inflammatory response to Malassezia's metabolites — oleic acid in particular. That inflammation drives accelerated skin turnover, which is what you see as flaking.

This is why moisturising shampoos fail. The problem is not dryness — the problem is an over-responsive inflammatory reaction to a yeast that is thriving on sebum. Feeding the scalp with more oil, or leaving the yeast undisturbed with a 'gentle' formula, is exactly backwards.

The actives that work

Five actives have solid evidence. Any dandruff shampoo worth buying contains one of these at a therapeutic strength:

• Ketoconazole 2% (Nizoral, prescription) or 1% (over the counter): the strongest evidence base, direct antifungal action on Malassezia.
• Ciclopirox 1.5%: excellent efficacy, sometimes better tolerated than ketoconazole.
• Selenium sulphide 2.5% (Selsun): powerful antifungal, can discolour blonde or chemically-treated hair.
• Zinc pyrithione 1–2% (Head & Shoulders clinical strength): antifungal and anti-inflammatory, gentler for daily use.
• Salicylic acid 3–6%: keratolytic — dissolves the built-up flake so the antifungal can reach the scalp. Best combined with an antifungal, not used alone.

The right way to use dandruff shampoo

Almost no-one uses dandruff shampoo correctly. Two changes double results.

• Leave it on. The active needs 5 minutes on the scalp to work. 30 seconds and rinse — which is how everyone showers — is not enough.
• Massage it into scalp, not hair. Focus on the scalp itself, not the lengths. Follow with a conditioner on the lengths only.
• Rotate actives. Malassezia adapts to a single active over months. Rotate ketoconazole with ciclopirox or zinc pyrithione every 4–8 weeks to keep effectiveness.
• Induction phase: 3x weekly for 4 weeks. Maintenance phase: 1–2x weekly indefinitely. Relapse is almost universal if maintenance is stopped.
• Salicylic acid pre-treatment: if scale is thick, use a salicylic-acid-based shampoo first to break the crust, then follow with the antifungal in the same wash.

Seborrheic dermatitis: when dandruff gets serious

Seborrheic dermatitis (SD) is the same disease process on a spectrum. Where dandruff is fine white flake, SD produces visible redness, greasy yellow scale, and often extends beyond the scalp — into eyebrows, nasolabial folds, behind the ears, and the mid-chest. It flares with stress, alcohol, illness and winter.

SD needs more than shampoo. A topical antifungal cream (ketoconazole 2% cream) for face and body, a short-term topical corticosteroid (hydrocortisone 1% for face, mometasone or clobetasol for scalp), and occasionally a topical calcineurin inhibitor (tacrolimus, pimecrolimus) for maintenance are all standard. Oral antifungals (itraconazole, fluconazole) are reserved for severe cases.

London-specific triggers

Hard water. Central London water is genuinely hard — high calcium and magnesium leave a mineral film on the scalp, block cleansing efficacy, and irritate sensitive skin. A shower filter (Jolie, Hello Klean, T3 Source) is not a gimmick for reactive scalps.

Central heating. London winters produce very low indoor humidity, which worsens all scalp inflammation. A bedroom humidifier helps.

Chlorinated pools. Rinse hair and scalp thoroughly after any swim.

Cycling helmets in summer. Occlusive, warm, sweat-trapping — a Malassezia paradise. Rinse-only mid-day washes help if flares track to summer commuting.

When it isn't dandruff

Four conditions look like dandruff and aren't: scalp psoriasis (thicker, silvery scale, often extends past the hairline in a sharp border), tinea capitis (patchy hair loss with scale, more common in children, needs oral antifungal), contact dermatitis (recent product change, itch is more prominent than flake), and lichen simplex (thickened patches from chronic scratching).

If a proper 4-week course of a therapeutic-strength antifungal shampoo used correctly hasn't shifted your scale, book a scalp exam. In London a trichologist consult with trichoscopy is £120–£250; a dermatology consult privately is £220–£400.