What differences can you see?
| Feature | Seborrhoeic dermatitis | Plaque psoriasis |
|---|---|---|
| Patch edges | Usually poorly defined. | Usually sharply defined. |
| Scale | Often yellow and greasy, but can also be white or dry. | Usually thicker, dry, white or silvery. |
| Typical locations | Scalp, central face and front of the chest. | Scalp, elbows, knees and lower back; nails can also be affected. |
| At the hairline | The scalp is a common site. | Patches often extend beyond the hairline onto the forehead and behind the ears. |
| Course | A chronic condition that comes back. | A chronic condition with periods of worsening and improvement. |
Colour alone is not a reliable way to separate them. Psoriasis can look pink or red on white skin and grey on brown or black skin, with dark marks remaining after patches clear. Not every type of psoriasis has thick scale: inverse psoriasis affects skin folds and can produce thin patches without scales.25
Why do they happen?
Yeast living on the skin and sebum, the skin's natural oil, are thought to play a role in seborrhoeic dermatitis. Psoriasis involves an overactive immune system that speeds up skin cell growth, creating a build up of cells and scale. Psoriasis is not contagious.456
Can you tell at home?
Use the pattern as a clue, not a diagnosis. Dandruff caused by seborrhoeic dermatitis can resemble psoriasis, and sebopsoriasis combines features of both. Psoriasis can also affect only the scalp, so having no elbow or knee patches does not rule it out.14
A clinician checks the rash, your symptoms and family history. Trichoscopy, a magnified examination of the scalp, helps distinguish patterns of scale and tiny blood vessels. Sometimes a biopsy, which examines a small skin sample, is needed. Arrange an assessment if the rash persists despite treatment bought without a prescription.123
How does treatment differ?
Treatment for seborrhoeic dermatitis can lessen the rash, itching and swelling and help prevent flares. Psoriasis treatment depends on the type, severity and location. Several products can belong in one treatment plan, even if the bathroom shelf would prefer fewer employees.56
Psoriasis treatments include moisturizers, topical steroids, vitamin D treatments and coal tar, with light therapy or medicines for more severe disease. Creams, lotions, ointments and gels are treatment formats, not a ranking system, despite the packaging aisle's enthusiasm for categories.5
Moisturizers relieve dryness, cracking and irritation. Salicylic acid and urea reduce scale but can sting damaged skin. Prescribed calcipotriol, a vitamin D derivative, is applied twice daily to reduce scale and thickening; redness can persist. Salicylic acid inactivates calcipotriol, so ask your prescriber how to arrange treatment rather than combining them yourself.7
A prescribed course of very potent topical steroid can improve psoriasis plaques within two to four weeks, but these steroids are for short term use. Prolonged use can thin the skin. Treatment strength and duration need to match the body area, particularly on the face and skin folds.7
When should you get medical help?
- See a doctor if treatment is not working or is causing side effects.
- Report recurring joint pain, stiffness or swelling. Psoriatic arthritis affects the joints, and early treatment can reduce damage.
- Seek urgent medical help for rapidly spreading skin redness with pus filled bumps, or severe pain and swelling with fever.
- If you are pregnant or planning pregnancy, review psoriasis medicines with a doctor or pharmacist because some treatments can be harmful.
Where this answer comes from
- 1Trichoscopy of Inflammatory Conditionsdermnetnz.org
- 2Psoriasis: What It Is, Symptoms, Causes, Types & Treatmentmy.clevelandclinic.org
- 3Eczema vs. Psoriasis: What’s the Difference?health.clevelandclinic.org
- 4Psoriasis: On the road to discoverymagazine-local.medlineplus.gov
- 5Psoriasisnhs.uk
- 6search.aad.orgsearch.aad.org
- 7Scaly skin diseases. Topical therapy for psoriasisdermnetnz.org
