What is psoriasis, and is it contagious?
Psoriasis — 銀屑病 in the clinical register — is a long-term skin condition producing itchy, painful patches of dry, flaky skin. The NHS states it plainly: psoriasis is not contagious, so it cannot be caught and cannot be passed on.
The two names are the same thing. Hong Kong government documents use 銀屑病 throughout; everyday speech mostly uses 牛皮癬. The difference is register, not diagnosis, neither word is more correct than the other, and either will be understood at a consultation.
That it does not spread is worth stating on its own, because being assumed contagious is part of the actual burden of the disease. Visible red plaques with silvery scale are easily mistaken for a fungal or infectious rash, and people are avoided at pools, gyms, barbers and work because of it. That is a misunderstanding, not a hygiene issue.
The second thing to be clear about: psoriasis cannot currently be cured. The NHS puts it as "it cannot be cured, but there are treatments to help manage your symptoms". No treatment aims at eradication, and any product or course promising a cure is at odds with that consensus.
What does psoriasis look like, and how does it differ from eczema?
The typical presentation is well-demarcated red plaques covered in silvery scale, commonly on the elbows, knees, scalp and lower back, and it can affect the nails. Telling psoriasis from eczema needs examination, not picture-matching.
The NHS notes that symptoms often start either between the ages of 15 and 25, or between 50 and 60. That two-peak pattern explains why psoriasis appears both in young adults and for the first time in middle age — the latter often put down to dry skin or ageing and left.
Nail changes are the part most often missed. Pitting, discolouration, thickening or separation from the nail bed can all be psoriasis, and they look much like a fungal nail. The two are managed quite differently — a separate page here covers the fungal side — and distinguishing them is a doctor’s job.
The difference from eczema is not one feature but the overall morphology, distribution and course, plus whether nails and joints are involved. A separate eczema page sits alongside this one; both are chronic skin conditions travelling the same public dermatology route, and they are nonetheless different diseases treated differently.
What causes psoriasis, and why does it keep flaring?
Psoriasis is a long-term immune-mediated condition, not a consequence of poor washing or diet. The NHS lists nine things that can trigger a flare.
The triggers the NHS lists:
- Stress
- Alcohol
- Smoking
- Obesity
- Pregnancy
- Certain medicines
- Infections, including strep A and HIV
- Skin injury
- Sunlight
That list has a practical use: it turns "what did I do wrong" into something that can be worked through item by item. The nine fall into three groups, and they are not handled the same way.
- Stress, alcohol, smoking and weight: the group you can act on yourself — and acting on it also lowers the cardiovascular risk the guideline asks to be assessed.
- Pregnancy and certain medicines: the group to raise with a doctor. Skin worsening after a new medicine is started is a reason to tell the prescriber, not a reason to stop it yourself.
- Infection and skin injury: the group that cannot be planned for, and the reason a flare sometimes arrives with no warning at all.
That skin injury can trigger new lesions has a direct bearing on day-to-day care: scratching, picking off scale, over-washing and harsh skincare steps can all extend the affected area. Sunlight is one of the few factors that cuts both ways — moderate exposure helps some people, while sunburn is skin injury.
