Dandruff is white flakes of skin on the scalp and in the hair, often with a dry, itchy scalp. It is common, it is not caused by poor hygiene and you cannot catch it. It is linked to a yeast called Malassezia that lives naturally on the skin and feeds on sebum, the oil your scalp makes, which is why the usual advice is a product containing an anti-dandruff active ingredient. Dry scalp, leftover product and several skin conditions can look like it, so the first job is working out which one you have.
This is the starting point for our series on flaky scalps. Each section below gives you the short version of one topic and then hands you to the article that covers it in depth.
- 1. What is dandruff?
- 2. What causes dandruff?
- 3. Is it dandruff or something else?
- 4. What helps: which anti-dandruff ingredients are there?
- 5. Why is zinc pyrithione gone from EU shampoos?
- 6. Does hard water play a part?
- 7. Do sweat, training and headgear make it worse?
- 8. Why is dandruff often worse in winter?
- 9. How do you use an anti-dandruff shampoo?
- 10. When should you see a pharmacist or doctor?
- 11. Summary
- 12. Frequently asked questions
- 13. Sources
Start here. Find the row that matches what you see, then follow the link.
| What you see | Most likely | Read more |
|---|---|---|
| Larger flakes that can look oily, an itchy scalp, comes and goes whatever plain shampoo you use | Dandruff | Dandruff, dry scalp or leftover product |
| Small, dry flakes, worse with hot showers or frequent washing | Dry scalp | Dandruff, dry scalp or leftover product |
| Chalky or waxy specks that appear as hair dries, soon after a change of product or water | Residue or soap scum | Does hard water cause dandruff? |
| Flaking and itch that seem worse after training or a long time under a helmet or cap | Existing flaking made more noticeable by sweat and heat | Dandruff and sweat |
| Flakes that come back every autumn and winter | A seasonal dandruff flare, a dry scalp, or both | Dandruff in winter |
| You are not sure what to look for on an anti-dandruff label | A question about actives | Anti-dandruff ingredients explained |
| Advice that still recommends zinc pyrithione | Advice from before the EU ban, or from outside the EU | Why zinc pyrithione disappeared from EU shampoos |
| Redness, soreness, swelling, bleeding, patches beyond the scalp, hair loss, or no change after at least four weeks of an anti-dandruff shampoo | Possibly another condition | See a pharmacist or doctor |
What is dandruff?
A common condition of the scalp skin, not a sign that you are washing wrong. The NHS describes it as white flakes of skin on the scalp and in the hair, more noticeable in darker hair or when they fall onto your shoulders, and says the scalp may also feel dry and itchy. It calls dandruff a common skin condition that is not harmful and that you cannot catch. Mayo Clinic agrees that it is common and is neither contagious nor harmful, and adds that it often starts in young adulthood.
Dermatology places dandruff on a scale. DermNet, the dermatology reference, describes dandruff as an uninflamed form of seborrhoeic dermatitis on the scalp. In other words, it belongs to a condition that, in its fuller form, adds redness and scaly patches and can affect the face and body too. Redness and spreading are exactly the signs that mean it is time to get it looked at.
The longer comparison of dandruff with its lookalikes is in dandruff, dry scalp or leftover product.
What causes dandruff?
A yeast called Malassezia, which feeds on scalp oil, is believed to play a role, and stress and cold weather may make dandruff worse. The NHS says dandruff can have different causes, including a type of yeast that naturally lives on your skin and skin conditions such as eczema, and that stress and cold weather may make it worse. DermNet names that yeast as Malassezia, a normal resident of the skin, and explains that its enzymes break down the fats in sebum.
Mayo Clinic lists several contributors alongside Malassezia: irritated or oily skin, dry skin, sensitivity to hair products and other skin conditions such as psoriasis and eczema. It also notes that dandruff is more common in males.
Just as useful is what is not on the list. The NHS is clear that dandruff is not caused by poor hygiene, although flakes can be more obvious if you do not wash your hair regularly. Washing more often can make flakes less visible, but it does not treat the cause. And none of the main health or dermatology sources we checked lists hard water or sweat as a cause, two ideas that come up often and that have their own sections below.
Is it dandruff or something else?
Flakes and itch are symptoms, not a diagnosis, and at least three everyday things look like dandruff.
- Dry scalp. Cleveland Clinic sums up the difference in one line: excess oil causes dandruff, and loss of moisture causes dry scalp. Dry scalp flakes tend to be smaller and drier.
- Leftover product. Product that is not fully rinsed out, or soap scum from a soap bar in hard water, can dry into white specks at the roots.
- A reaction to a product. The American Academy of Dermatology explains that an allergic reaction to a hair product causes an itchy scalp and a rash on the scalp and any other skin the product touches, and that you must stop using the product.
Then there are skin conditions that can resemble dandruff. The AAD says that flaking which does not respond to home treatment may be a sign of seborrhoeic dermatitis, psoriasis, a fungal infection of the scalp or eczema, and its page on dry scalp conditions adds that scalp ringworm usually comes with patches of hair loss or broken hairs. None of these is resolved by changing shampoo, so they are a question for a pharmacist or doctor.
The full comparison, with what to do about each one, is in dandruff, dry scalp or leftover product. For a short version inside our hair type guide, see the scalp section of are shampoo bars good for curly, fine or coloured hair.
What helps: which anti-dandruff ingredients are there?
An anti-dandruff product works through a named active ingredient, not through the words on the front of the pack. Antifungals reduce the growth of Malassezia; keratolytics loosen and remove the scale.
The NHS tells you to look for shampoos containing ketoconazole, coal tar or salicylic acid. The AAD also lists selenium sulfide, sulfur and zinc pyrithione, though zinc pyrithione is no longer allowed in EU cosmetics. Two more names you may meet on EU labels are climbazole, which Commission Regulation (EU) 2019/698 lists as an anti-dandruff agent in rinse-off shampoo, and piroctone olamine, which COSMILE, the ingredient database run by the industry association Cosmetics Europe, lists with an anti-dandruff function.
How they are sold differs. Salicylic acid and climbazole can appear in EU cosmetic shampoos within limits set in the EU cosmetics rules; the salicylic acid limits are in Commission Regulation (EU) 2019/1966. Ketoconazole is an antifungal medicine: in the UK most ketoconazole shampoos can be bought in pharmacies and shops and are also available on prescription. Coal tar is on the EU list of substances prohibited in cosmetics, as a 2003 SCCNFP opinion recording the committee's earlier conclusions on coal tars notes, so coal tar shampoos, where they are available, are medicines. Availability varies by country, so ask a pharmacist.
We do not rank the actives: which one suits a given scalp is a question for a pharmacist. Rinsed bars contain no anti-dandruff active. None of the actives above is on either Rinsed ingredient list, and we make no claim that the bars help with dandruff. What each active does, and how the EU classifies it, is in anti-dandruff ingredients explained.
Why is zinc pyrithione gone from EU shampoos?
Because of a legal mechanism, not a finding that the shampoos harmed people. Under EU chemicals law it was classified as toxic for reproduction, category 1B, and EU cosmetics law bans substances with that classification unless every condition for an exception is met.
Commission Regulation (EU) 2021/1902 added zinc pyrithione to Annex II, the list of substances prohibited in cosmetic products, with effect from 1 March 2022. The regulation itself records that the EU's Scientific Committee on Consumer Safety concluded zinc pyrithione can be considered safe as an anti-dandruff ingredient in rinse-off hair products at up to 1%. It was banned anyway because it had not been established that no suitable alternative substances were available, and that is one of the conditions for an exception.
A hazard classification describes what a substance can do in principle, so the ban is not a verdict on the shampoos people used for years. In practice, advice that still recommends zinc pyrithione usually predates the ban or comes from outside the EU, and a cosmetic shampoo made available in the EU since 1 March 2022 should not contain it. Rinsed bars do not contain zinc pyrithione. The regulation, the timeline and what the classification means are in why zinc pyrithione disappeared from EU shampoos.
Does hard water play a part?
There is no good evidence that hard water causes dandruff, but it can create flakes that look like it. Hard water carries dissolved calcium and magnesium. According to the Royal Society of Chemistry, those ions react with soap to form an insoluble scum. On a scalp it can dry into chalky or waxy flecks that pass for dandruff, usually soon after a change of product or water.
The research on hard water and skin is about eczema, not dandruff. A lab study of 80 people found that skin washed in hard water held more detergent and became more irritated, especially in people with eczema who carry a particular gene variant (FLG). But a trial in 336 children with eczema found that fitting a water softener gave no additional benefit over usual care. Neither study looked at the scalp, and we found no study on hard water and dandruff itself.
This is the one part of the topic where the bar you choose matters, and only for residue. Rinsed bars are syndets with no saponified oils, and it is soap that forms soap scum with the calcium and magnesium in hard water. That is a statement about the ingredient list, not a promise about your scalp, and it does nothing for dandruff. Any product that is not rinsed out can still leave residue. The full evidence is in does hard water cause dandruff.
Shampoo, body and face wash, all in one bar. Cooling, refreshing and designed for those always on the go.
Do sweat, training and headgear make it worse?
Sweat does not cause dandruff, but it may make existing flaking more noticeable in some people. None of the medical sources we checked lists sweat as a cause, and skipping a shower after the gym does not give you dandruff. The AAD does list becoming sweaty among the triggers for seborrhoeic dermatitis, and says the salt from sweat can trigger a flare. Since dandruff is an uninflamed form of the same condition, it is reasonable to say sweat may aggravate it, and not reasonable to say sweat causes it.
Heat and headgear are plausible aggravators, but we found no clinical study on helmets or caps and dandruff. What is well documented is a different problem: the AAD describes acne mechanica, where sports equipment traps heat and sweat and rubs the skin, starting as small, rough bumps. Spots along a helmet line are not dandruff, and are worth getting checked if they persist.
The habits the sources support are ordinary ones: wash your scalp as often as it needs, which for an oily scalp can mean daily according to the AAD, do not sit for hours in a sweaty cap, keep headgear clean, and if you use an anti-dandruff shampoo, follow its directions. Situation by situation advice for the gym, cycling, swimming and running is in dandruff and sweat.
Why is dandruff often worse in winter?
Two different things may get worse in winter, and they need different responses. The NHS says cold weather may make dandruff worse, and Mayo Clinic says the same of cold, dry weather. DermNet lists winter flares that improve in summer as typical of seborrhoeic dermatitis in adults, and the AAD says flare ups are common when the weather turns cold and dry. The sources describe the pattern but not exactly why it happens.
Dry scalp is the clearer winter problem. Cleveland Clinic says low humidity and cold climates can dry out the scalp, and the AAD says hot water can dry your skin and your scalp. The AAD's advice for dry skin is to keep showers and baths to five to ten minutes in warm water and to consider a humidifier at home. For seborrhoeic dermatitis, it also suggests dressing for the weather, including a hat outdoors.
So in winter, turning the water down and washing less often can help a dry scalp, while dandruff still calls for an anti-dandruff product used as directed. A flare every winter is a known pattern, not a sign you are doing something wrong. The factor by factor table is in dandruff in winter.
How do you use an anti-dandruff shampoo?
Follow the directions on the product you choose. That is the most important rule, because products differ. Beyond that, the sources give only general guidance, and we will not go further than they do.
- Follow the label or leaflet. The AAD notes that these shampoos are lathered onto the scalp and that some are meant to stay on for a few minutes before rinsing, which is why the directions matter. A medicine comes with a patient leaflet; read it.
- Give it time. The NHS suggests using an anti-dandruff shampoo for up to four weeks to see whether your dandruff gets better, and says you might need to try more than one type to find one that works for you.
- Ask a pharmacist. The NHS says a pharmacist can tell you how to use the shampoo. A pharmacist can also help you choose between actives and tell you if you need to see a doctor.
We do not give schedules or routines here; the directions and your pharmacist cover those. If you use a medicated shampoo, keep using it as directed; a Rinsed bar is not a substitute for it. More on reading an active on a label is in anti-dandruff ingredients explained.
When should you see a pharmacist or doctor?
A pharmacist is a quick first stop for any flaky scalp. See a pharmacist or doctor, rather than trying another shampoo, if any of these apply. The NHS advises seeing a GP if you still have dandruff after using an anti-dandruff shampoo for at least four weeks, if your dandruff is bad or your scalp is very itchy, if your scalp is red or swollen, or if you have flaky, itchy patches on your face or other parts of your body.
- Flaking that persists, keeps coming back or is getting worse
- Redness, swelling, soreness or pain
- Bleeding from the scalp
- Flaky or red patches spreading beyond the scalp
- Patches of hair loss or broken hairs
- Severe itching
- No improvement after at least four weeks of an anti-dandruff shampoo used as directed
- A rash or itch that started with a new product: stop using the product
Psoriasis, seborrhoeic dermatitis, eczema, fungal infections and contact reactions can all look like dandruff from the outside, and none of them is solved by a change of shampoo. For everything else that can go wrong after switching to a bar, beyond the scalp, see shampoo bar problems, solved.
Summary
Dandruff is a common, harmless scalp condition that is not caused by poor hygiene. It is linked to Malassezia, a yeast that lives on the skin and feeds on sebum, and it is an uninflamed form of seborrhoeic dermatitis. Stress and cold weather may make dandruff worse. The standard advice is a product with an anti-dandruff active, such as ketoconazole, selenium sulfide or salicylic acid, used as directed. Climbazole and piroctone olamine also appear in EU cosmetic shampoos, and zinc pyrithione has been banned from EU cosmetics since 1 March 2022. Rinsed bars contain no anti-dandruff active.
Dry scalp, residue and product reactions can look like dandruff. There is no good evidence that hard water or sweat causes it, though soap scum in hard water can mimic it. Rinsed bars are syndets with no saponified oils, and it is soap that forms soap scum with the calcium and magnesium in hard water; that is not a promise about your scalp. Anything persistent, severe, red, sore, swollen, spreading or painful, or unchanged after at least four weeks, is a question for a pharmacist or doctor.
Frequently asked questions
Is dandruff caused by not washing your hair enough?
No. The NHS says dandruff is not caused by poor hygiene, although flakes can be more obvious if you do not wash your hair regularly. It is linked to a yeast called Malassezia that lives naturally on the skin and feeds on scalp oil.
Is dandruff contagious?
No. The NHS says you cannot catch dandruff, and Mayo Clinic describes it as neither contagious nor harmful.
How can I tell dandruff from a dry scalp?
Dandruff flakes tend to be larger and can look oily. Dry scalp flakes tend to be smaller and drier, and are often worse with cold weather, hot showers or frequent washing. Cleveland Clinic puts it simply: excess oil causes dandruff, loss of moisture causes dry scalp. If you are not sure, ask a pharmacist.
Do Rinsed bars help with dandruff?
No. Rinsed bars are 3-in-1 cleansing bars and contain no anti-dandruff active. If you have dandruff, use a product that contains an active made for it, follow its directions, and see a pharmacist or doctor if it does not improve.
How long should I use an anti-dandruff shampoo before it works?
The NHS suggests using it for up to four weeks to see if your dandruff gets better, and says you may need to try more than one type. Follow the directions on the product. If you still have dandruff after at least four weeks, see a GP or pharmacist.
Does hard water cause dandruff?
There is no good evidence that it does. Hard water can, however, react with true soap and leave a scum on hair and scalp that looks like flakes. That is residue, not skin, and it builds up less if you use less product and rinse thoroughly.
Is zinc pyrithione still allowed in shampoo?
Not in cosmetic products in the EU. Commission Regulation (EU) 2021/1902 added it to the list of prohibited substances from 1 March 2022. Advice that still recommends it usually predates the ban or comes from outside the EU.
Do Rinsed bars contain fragrance?
Yes. Every Rinsed bar contains Parfum, and the ingredient lists name the fragrance allergens present above the EU labelling threshold. If you know you react to fragrance, check the list before you buy, and if your scalp or skin reacts after using a bar, stop using it.
Sources
The facts in this article are based on the sources below, checked in September 2026.
- Dandruff. NHS.
- Dandruff: Symptoms and causes. Mayo Clinic.
- Seborrheic dermatitis: Causes and treatment. DermNet, 2024.
- How to treat dandruff. American Academy of Dermatology, 2023.
- Dry Scalp: Causes, Treatment & Prevention. Cleveland Clinic, 2022.
- 10 reasons your scalp itches and how to get relief. American Academy of Dermatology.
- Is your dry scalp something more serious? American Academy of Dermatology.
- About ketoconazole. NHS, 2024.
- Regulation (EC) No 1223/2009 of the European Parliament and of the Council of 30 November 2009 on cosmetic products (recast). Official Journal of the European Union, 2009.
- Commission Regulation (EU) 2019/698 of 30 April 2019 amending Annexes III and V to Regulation (EC) No 1223/2009 of the European Parliament and of the Council on cosmetic products. Official Journal of the European Union, 2019.
- Commission Regulation (EU) 2019/1966 of 27 November 2019 amending and correcting Annexes II, III and V to Regulation (EC) No 1223/2009 of the European Parliament and of the Council on cosmetic products. Official Journal of the European Union, 2019.
- Piroctone Olamine: Ingredient. COSMILE Europe.
- Opinion of the Scientific Committee on Cosmetic Products and Non-Food Products Intended for Consumers concerning Wood Tars and Wood Tar Preparations, SCCNFP/0646/03, final. SCCNFP, European Commission, 2003.
- Commission Regulation (EU) 2021/1902 of 29 October 2021 amending Annexes II, III and V to Regulation (EC) No 1223/2009 of the European Parliament and of the Council as regards the use in cosmetic products of certain substances classified as carcinogenic, mutagenic or toxic for reproduction. Official Journal of the European Union, 2021.
- What ions cause hardness in water? Royal Society of Chemistry.
- The Effect of Water Hardness on Surfactant Deposition after Washing and Subsequent Skin Irritation in Atopic Dermatitis Patients and Healthy Control Subjects. Journal of Investigative Dermatology, 2018.
- A Randomised Controlled Trial of Ion-Exchange Water Softeners for the Treatment of Eczema in Children. PLoS Medicine, 2011.
- Seborrheic dermatitis: Self-care. American Academy of Dermatology.
- Is sports equipment causing your acne? American Academy of Dermatology.
- Dermatologists' top tips for relieving dry skin. American Academy of Dermatology, 2026.
