TL;DR: Key Takeaways
- Dandruff: small greasy white/yellow flakes, mild itch, scalp only.
- Scalp psoriasis: thick silvery scale on red plaques with clear borders.
- Psoriasis often extends past the hairline (forehead, behind ears, neck).
- Anti-dandruff shampoo not working after 4 weeks → suspect psoriasis.
Quick answer
Dandruff (seborrheic dermatitis) makes small, greasy, white-to-yellow flakes with mild itch, stays inside the hairline, and clears with an OTC anti-dandruff shampoo in a few weeks. Scalp psoriasis makes thick, silvery-white scale sitting on top of well-defined red plaques, itches intensely, and commonly extends past the hairline onto the forehead, behind the ears, or the back of the neck. If your dandruff shampoo hasn't worked after 4 weeks, get a dermatologist to check for psoriasis.
At-a-glance comparison
| Feature | Dandruff | Scalp Psoriasis |
|---|---|---|
| Scale | Small, greasy, white/yellow | Thick, silvery, dry |
| Underlying skin | Mildly pink | Well-defined red plaque |
| Borders | Diffuse, fuzzy | Sharp, clearly defined |
| Location | Scalp only | Extends past hairline, behind ears, neck |
| Itch | Mild – moderate | Intense, sometimes burning |
| Response to OTC shampoo | Clears in 2–4 weeks | Minimal improvement |
| Elsewhere on body | Sides of nose, eyebrows, chest | Elbows, knees, lower back, nails |
The hairline test
The single most useful clue: look at your hairline in a mirror. If the flaky, red skin stops at the hair, it's almost always dandruff. If it clearly crosses the hairline onto your forehead, temples, behind your ears, or the nape of your neck, it's most likely scalp psoriasis. Psoriasis doesn't respect the boundary of the scalp; seborrheic dermatitis usually does.
Treatment that actually works
- Dandruff: alternate two shampoos — zinc pyrithione, ketoconazole 1%, or selenium sulfide. Leave on 5 minutes before rinsing.
- Scalp psoriasis: coal tar or 3% salicylic acid shampoo to soften scale first
- Prescription topical steroid or vitamin D analogue (calcipotriol) lotion for plaques
- Never pick or comb out thick scale — it triggers Koebner and worsens plaques
- Extensive scalp psoriasis + nail pitting + joint pain → ask about systemic treatment
See a doctor if:
- OTC anti-dandruff shampoo hasn't worked after 4 weeks
- Plaques are spreading past the hairline
- Hair shedding, joint stiffness, or nail changes
- Scalp is weeping, crusting, or painful (possible bacterial infection)
Why one check is rarely enough
A single scan tells you about one spot, on one day. But skin changes are about patterns over time — a new mole appearing, a slow shift in shape, size or colour, or a patch that simply isn't healing. Monitoring the same spots side-by-side, week after week, surfaces the subtle changes a one-off check will always miss — and gives you a clear record to show a clinician if something needs a closer look.
(ScanSkinAI is a screening and monitoring tool, not a diagnosis. Always see a clinician for anything that is changing, bleeding, or worrying you.)
Unlimited scans · Track changes side-by-side · Cancel anytime
Let AI narrow it down
Upload a photo of your scalp. ScanSkinAI matches your pattern against trained dermatology categories including psoriasis and seborrheic dermatitis.
Frequently Asked Questions
Dandruff flakes are small, white or yellow, greasy, and confined to the scalp. Scalp psoriasis produces thick, silvery-white scale on well-defined red plaques that often extend past the hairline onto the forehead, behind the ears, or the back of the neck.
Dandruff itch is mild to moderate. Scalp psoriasis itch is often intense and can burn or sting. Scratching psoriasis frequently triggers new plaques (the Koebner phenomenon).
No — they're separate conditions. But seborrheic dermatitis (the medical name for dandruff) and scalp psoriasis can coexist, called sebopsoriasis. If OTC anti-dandruff shampoo hasn't cleared it in 4 weeks, ask a clinician to check for psoriasis.
Dandruff: zinc pyrithione, ketoconazole 1%, or selenium sulfide. Scalp psoriasis: coal tar or salicylic acid shampoos, plus prescription topical steroid or vitamin D analogue lotion applied to the scalp.
The condition itself doesn't destroy hair follicles, but severe scratching, harsh scale removal, or long-standing inflammation can cause temporary shedding. Hair usually regrows once the plaques clear.