The short answer
A medicated shampoo with an antifungal ingredient, left on the scalp for several minutes rather than rinsed straight off. Ordinary shampoo does not treat it.
- Use a shampoo containing ketoconazole, selenium sulfide, zinc pyrithione or coal tar.
- Leave it on the scalp for three to five minutes before rinsing. This is the step that makes the difference, and almost nobody does it.
- Use it two or three times a week initially, then less as it improves.
- Rotate between two different actives if one stops working.
- Massage into the scalp, not the hair.
What will ruin it
A scalp that is intensely itchy, weeping, scaly beyond the hairline, or accompanied by patches elsewhere on the body needs a GP or pharmacist. Psoriasis and seborrhoeic dermatitis are treated differently.
Why it works
Ordinary dandruff is largely an inflammatory response to a yeast that lives on everybody's skin. It is not caused by dryness and not by poor washing, which is why moisturising and washing harder both fail.
This is general information, not medical advice, and it does not replace a GP, a pharmacist or NHS 111. Call 999 in an emergency. Full disclaimer.