Dandruff is one of the most common scalp complaints, and one of the most misunderstood. This guide sets out what the NHS and the British Association of Dermatologists (BAD) say about what it is, what shampoo ingredients they name, how long to give a product, and when a flaky scalp deserves a closer look.
What is dandruff, exactly?
According to the NHS, dandruff is a common skin condition that is not harmful and not contagious. It produces white flakes of skin on the scalp and in the hair, which are more noticeable on darker hair or when they fall onto the shoulders. The scalp may also feel dry and itchy.
The BAD describes dandruff as the scalp form of a wider condition, seborrhoeic dermatitis, and says it is very common, affecting almost half of all adults. In other words, if flakes have appeared on your collar, you are in large company.
Dandruff is not a sign of poor hygiene. The NHS states plainly that poor hygiene does not cause it, although flakes may be more obvious if hair is not washed regularly. That distinction matters, because the assumption that dandruff means “not clean enough” leads many people to scrub harder, which can leave an already sensitive scalp more irritated.
What actually causes the flaking?
The honest answer is that the cause is not fully understood. The NHS says dandruff may be linked to a yeast that naturally lives on the skin, or to skin conditions such as eczema. The BAD goes into more detail for seborrhoeic dermatitis: a yeast called Malassezia, which normally lives on the skin, is found in higher amounts in affected people. Current thinking, it says, is that a weakened skin barrier and an increased sensitivity to a substance the yeast produces lead to inflammation. It adds that this yeast is different from the one that causes thrush, and that there is thought to be a genetic susceptibility combined with external factors.
Two things are worth taking from this:
- The yeast is a normal resident of the skin. The issue is the skin’s reaction to it, not an infection picked up from someone else.
- Because the reaction varies from person to person, so does what works.
Why does it come and go?
Many people notice that flaking is worse at certain times. The NHS says stress and cold weather can make dandruff worse, and the BAD lists tiredness, stress and cold, dry weather as triggers for flares in seborrhoeic dermatitis. That helps explain why scalps often seem flakier in autumn and winter, when cold air outdoors meets heated air indoors.
The BAD also notes that the condition has no cure but can be controlled, and that symptoms often return when treatment stops. That is a useful expectation to hold from the start: a product that works is usually one you keep using in some pattern, not one you use once and forget.
Which shampoo ingredients do health bodies name?
The NHS advises using an anti-dandruff shampoo, available from pharmacies and supermarkets, and says to choose one with one or more of three ingredients: ketoconazole, coal tar or salicylic acid. The BAD, writing about seborrhoeic dermatitis of the scalp, names medicated shampoos containing zinc pyrithione, selenium sulphide or ketoconazole.
The two lists overlap on ketoconazole and differ elsewhere, which reflects the different audiences: the NHS page is written for everyday dandruff, the BAD leaflet for the broader condition. The table below sets out what each source says, without ranking one over another.
| Ingredient | Named by the NHS (dandruff) | Named by the BAD (scalp) |
|---|---|---|
| Ketoconazole | Yes | Yes |
| Coal tar | Yes | Not named |
| Salicylic acid | Yes | Named as a descaling ingredient, not in shampoo |
| Zinc pyrithione | Not named | Yes |
| Selenium sulphide | Not named | Yes |
Reading the ingredient list on the back of a bottle is the practical step. Our guide to reading a cosmetics label explains how ingredient lists are ordered and what the names mean, which helps when you are comparing products in a pharmacy aisle. A pharmacist can also explain how to use a given shampoo, as the NHS points out.
How should a medicated shampoo be used?
The NHS does not specify how often to wash with an anti-dandruff shampoo, so the product’s own instructions and a pharmacist’s advice are the guide. The BAD gives one concrete technique for the scalp: massage the shampoo in and leave it for 5 to 10 minutes before rinsing. For the body, it says to leave it on for 5 minutes.
That contact time is the part many people skip. A quick lather and rinse does not give an active ingredient long on the skin. If the label gives different timings, follow the label, as the instructions on a licensed product take precedence over general guidance.
Once the skin is clear, the BAD says that continuing with an antifungal shampoo once or twice a week can help prevent recurrence, and that a doctor may advise taking breaks from treatment.
How long should you try a product before changing it?
The NHS gives a clear timeframe: use the shampoo for up to 4 weeks to see whether it helps, and be prepared to try more than one type. If symptoms persist after at least 4 weeks of anti-dandruff shampoo, it advises seeing a GP.
A simple worked example shows how to apply this:
- Week 0: pick one shampoo with an ingredient the NHS names, and note how your scalp looks and feels.
- Weeks 1 to 4: use it as directed, changing nothing else about your hair routine if you can, so you can tell what is making a difference.
- Week 4: if flaking has eased, carry on as advised. If it has not, that is the moment to try a different ingredient or ask a pharmacist, and if symptoms are still present, to see a GP.
Changing several products at once is the most common reason people cannot tell what helped. The same one-change-at-a-time logic applies to starting retinol, where it is also the best way to identify what is irritating the skin.
Is it really dandruff? Look-alike conditions
Not every flaky scalp is dandruff. The NHS lists several conditions with similar symptoms:
- Seborrhoeic dermatitis: scaly, itchy, red patches on the scalp, face and body.
- Ringworm of the scalp (tinea capitis): a red or silver rash, sometimes with patchy hair loss.
- Eczema: dry, red, flaky, very itchy skin.
- Contact dermatitis: irritated skin, sometimes blistered or cracked, from products such as hair dye, sprays, gels or mousses.
- Psoriasis: red, crusty, sore patches covered in silvery scales.
- Cradle cap: greasy, yellowish crusts on a baby’s scalp, eyebrows and nappy area.
The contact dermatitis entry is a reminder that styling products themselves can be the cause. If a rash follows a colour appointment, our explainer on hair dye reactions and the patch test covers what to look for. And if what concerns you is thinning rather than flaking, male pattern hair loss is a separate subject with its own evidence.
When is it time to see a GP?
The NHS lists these non-urgent reasons to see a GP:
- symptoms persist after at least 4 weeks of anti-dandruff shampoo;
- dandruff is severe, or the scalp is very itchy;
- the scalp is red or swollen;
- flaky, itchy patches appear on the face or other parts of the body.
A GP can check the scalp for other skin conditions. The BAD adds that diagnosis is usually made by examining the rash, often in primary care, with referral to a dermatologist if needed, and that tests are not usually necessary. For babies, the BAD says the scalp form (cradle cap) usually clears within months and that adult approaches should not be used on them, so a pharmacist or health visitor is the right first call.
Everyday habits that support a calmer scalp
Beyond shampoo, the BAD’s self-care advice for seborrhoeic dermatitis is modest: use a gentle, soap-free wash on affected skin, apply a light moisturiser to support the skin barrier, and, if you wear make-up on affected areas, choose non-comedogenic products that do not block pores. It also says research suggests eating fruit may help reduce flares, which is worth stating with its caveat: it is an association, not a treatment.
For the ears, the BAD advises avoiding cotton buds, which worsen irritation. For the eyelids, it describes gently cleaning between the lashes with a non-irritating eyelid cleanser, and anything affecting the eyes is a good reason to talk to a pharmacist or doctor rather than experimenting.
A calm approach to a very common problem
Dandruff is common, harmless and manageable, and the guidance from the NHS and the BAD is consistent: use an anti-dandruff shampoo with an ingredient they name, give it time and proper contact with the scalp, change one thing at a time, and speak to a pharmacist or GP if four weeks pass without improvement or if the scalp is red, swollen, very itchy or flaky patches appear elsewhere. Knowing it is not a hygiene failure removes the most unhelpful part of the problem.
This article offers general information, not medical advice. If you are worried about your scalp or skin, speak to a pharmacist, GP or dermatologist.
Sources: NHS (Dandruff); British Association of Dermatologists (Seborrhoeic dermatitis patient information leaflet)
