Dandruff, Seborrhoeic Dermatitis or Psoriasis?

All three produce flakes on your shoulders, and all three get treated with whatever anti-dandruff shampoo is nearest. Two of them respond to that. The third does not, which is why some people conclude nothing works.

Telling them apart is not difficult once you know what to look at, and it decides which bottle to buy. This page is about the conditions themselves; our guide to ketoconazole without the jargon covers the ingredient that treats two of them.

On this page:

• The three at a glance
• Ordinary dandruff
• Seborrhoeic dermatitis
• Scalp psoriasis
• Three questions that decide it
• Which product each one points to
• When to stop self-treating
• Frequently asked questions

The three at a glance

Read the table by column rather than by row, because the pattern across all five characteristics is what identifies a condition rather than any single one of them.

	Dandruff	Seborrhoeic dermatitis	Scalp psoriasis
Flakes	Fine, white, dry	Greasy, yellowish	Thick, silvery
Redness	Little or none	Yes, underneath	Yes, sharply bordered
Edges	Diffuse	Diffuse	Clearly defined patches
Beyond the scalp	No	Eyebrows, sides of nose	Elbows, knees, nails
Responds to ketoconazole	Yes	Yes	Not primarily

The last two rows do most of the work. Where else it appears, and whether an antifungal touches it, separate psoriasis from the other two far more reliably than the flakes do.

Ordinary dandruff

Fine white flakes, an itchy scalp, and not much visible redness underneath. It comes and goes, is often worse in winter, and it is extremely common.

The driver is Malassezia, a yeast that lives on almost everyone's skin. Dandruff is what happens in the people whose skin reacts to it, which is why an antifungal treats it and why a cosmetic anti-dandruff shampoo aimed only at washing flakes away tends to disappoint. NHS guidance on dandruff covers the basics and when to ask a pharmacist.

Ketoconazole shampoo works well here. The choice is really about strength rather than product, and our comparison of Nizoral 1% and 2% covers which one to start with.

Seborrhoeic dermatitis

The same yeast, further along. Greasy yellowish scale rather than dry white flakes, visible redness underneath, and itching that is harder to ignore.

The giveaway is where else it appears. DermNet NZ describes it affecting the eyebrows, the sides of the nose, behind the ears and the chest as well as the scalp. Dandruff stays on your head; this does not.

It responds to the same antifungal treatment, usually needing the 2% strength to clear a flare and ongoing maintenance to keep it clear, because it recurs rather than resolves. This is the condition most people who think they have stubborn dandruff actually have, and it is the reason a course that seems to work keeps needing repeating.

Scalp psoriasis

Thick, silvery scale sitting on sharply bordered plaques, often extending slightly past the hairline where you can see the edge clearly. Underneath, the skin is red and inflamed rather than merely irritated.

DermNet NZ describes scalp psoriasis as an immune-driven condition rather than a reaction to yeast, which is why ketoconazole is not the primary answer for it. Picking at the scale can trigger it to spread, which is worth knowing before you start scratching.

Look elsewhere on your body. Psoriasis commonly appears on elbows and knees and can affect the nails with pitting or ridging, and that combination is close to conclusive. If this is the row you are reading yourself into, stop here and go to our review of the Nizoral psoriasis shampoo, which covers the salicylic acid product, how to use it and where its ceiling sits.

Three questions that decide it

Ask them in this order, because they are ranked by how much each one tells you.

Where else does it appear? Nowhere suggests dandruff. Eyebrows and nose suggest seborrhoeic dermatitis. Elbows, knees or nails suggest psoriasis. This single question resolves most cases on its own.

What do the edges look like? Diffuse and fading out suggests the first two. Sharply bordered patches you could draw around suggest psoriasis.

Are the flakes dry, greasy or thick? Dry and white, greasy and yellow, thick and silvery, in that order. This is the least reliable of the three, which is why it is last rather than first, since flake appearance changes with how recently you washed.

One thing all three share: none of them causes permanent hair loss, though scratching and inflammation can trigger temporary shedding. Our page on whether dandruff causes hair loss covers that distinction.

Which product each one points to

Two of the three answers are the same product at different strengths, which is why getting the diagnosis right matters more than getting the brand right.

For an active flare of dandruff or seborrhoeic dermatitis, the 2% treatment shampoo at EUR 24.99 twice a week for two to four weeks is the clearing phase, and a 1% shampoo once weekly is what holds it afterwards. Our guide to how often to use Nizoral covers the schedule in detail.

For psoriasis the active ingredient changes entirely: Nizoral Scalp Psoriasis Shampoo and Conditioner at EUR 34.99 uses 3% salicylic acid to lift scale rather than an antifungal to reduce yeast. Our guide to Nizoral for psoriasis versus dandruff covers the split product by product, and all of them sit together in the Nizoral and scalp care collection.

When to stop self-treating

Six to eight weeks of correct treatment with no improvement at all is itself informative, because it points away from the two yeast-driven conditions. That is the moment to see a pharmacist or doctor rather than buying a third shampoo.

Go sooner if there is pain rather than itching, if the skin is bleeding or weeping, if plaques are spreading, or if there are signs of infection. A proper diagnosis also rules out the less common explanations, since thick scale on a scalp is not always psoriasis. Where scalp symptoms come alongside noticeable hair loss, NHS guidance on hair loss covers when that combination warrants a look.

Frequently asked questions

How do I know if it is dandruff or seborrhoeic dermatitis?

Seborrhoeic dermatitis has visible redness under the flakes, greasier yellowish scale, and usually appears beyond the scalp on the eyebrows or the sides of the nose. Dandruff stays on the head and leaves the skin underneath looking more or less normal.

Will anti-dandruff shampoo help psoriasis?

Not primarily. Psoriasis is immune-driven rather than yeast-driven, so an antifungal is aimed at something that is not the problem. It needs a product that lifts scale, which is a different active ingredient entirely.

Can I have more than one?

Yes, and it happens more often than people expect. If treatment clears part of the picture but leaves the rest untouched, that is worth raising with a pharmacist rather than switching products again on your own.

Does it matter which one I have?

Yes, because two of the three respond to ketoconazole and one does not. Buying the wrong product is the usual reason a medicated shampoo appears to fail, and it costs you weeks as well as the price of the bottle.

When should I see a doctor?

If there is pain rather than itching, bleeding, spreading redness, or no improvement at all after six to eight weeks of correct treatment. A diagnosis at that point saves you buying a third product that treats the wrong thing.