Conditions

Psoriasis

What it is

An immune-driven condition, not an infection

Contagious

No — it cannot be passed to anyone

Realistic goal

Long periods of clear or near-clear skin

Psoriasis is an immune-driven condition in which skin cells are produced much faster than they are shed. The result is thickened, red or dusky plaques with silvery scale, most often on the elbows, knees, lower back and scalp, though it can appear anywhere including the nails.

It is not an infection, it is not caused by poor hygiene, and it cannot be passed to anyone else. Those three misconceptions cause more distress than the condition itself in many patients.

Forms it takes

• Chronic plaque psoriasis — the common form. Well-defined scaly plaques on extensor surfaces.
• Scalp psoriasis — thick scale along the hairline, often mistaken for severe dandruff.
• Guttate psoriasis — a sudden shower of small spots, often a week or two after a throat infection. Frequently settles on its own.
• Inverse psoriasis — in the folds, where it is shiny and red rather than scaly, and often misdiagnosed as fungal.
• Nail psoriasis — pitting, discolouration and lifting. Commonly treated for months as a nail fungus before the diagnosis is made.
• Pustular and erythrodermic psoriasis — uncommon, severe, and needing urgent in-person care.

How it is assessed

Mostly clinically — the appearance, distribution and the characteristic scale are usually enough. Dermoscopy helps where it is unclear. A KOH mount is worth doing where fungus is in the differential, especially in the folds. A biopsy is occasionally needed when the picture is atypical or the response is unexpected.

Because psoriasis is associated with joint disease, cardiovascular risk, diabetes and fatty liver, the consultation covers more than skin: joint symptoms, weight, blood pressure and relevant blood tests where indicated.

Treatment by severity

Limited disease

Topical treatment: vitamin D analogues such as calcipotriol, topical steroids used in courses, coal tar preparations, and salicylic acid to lift thick scale so the active treatment can reach the skin. Emollients used generously make everything else work better.

Moderate disease

Phototherapy — narrowband UVB, given in a controlled course — is effective and well established. Oral methotrexate, acitretin or ciclosporin are used where phototherapy is not practical, each with its own monitoring requirements.

Severe or treatment-resistant disease

Biologics targeting specific parts of the immune pathway have changed outcomes substantially for severe psoriasis. They require screening before starting, including for tuberculosis, and ongoing monitoring.

Living with it

Moisturising daily, treating throat infections promptly, stopping smoking and reducing alcohol all measurably reduce flares. So does having a plan for what to do when a flare starts, rather than restarting the search for a doctor each time.

What else it could be

These are the conditions this is most often mistaken for. Treating the wrong one is the commonest reason a problem drags on for months.

Often mistaken for	How it's told apart
Fungal infection	Ringworm has an active, scaly advancing edge with clearing in the middle. A KOH mount settles it in minutes. Antifungals do nothing for psoriasis.
Seborrhoeic dermatitis	Greasier, yellowish scale in the eyebrows, nasal folds and scalp, with less sharply defined edges.
Eczema	Itchier, less sharply bordered, with finer scale and a different distribution — flexures rather than knees and elbows.
Lichen planus	Violet-coloured flat-topped bumps, often with mouth involvement and fine white lines on the surface.
Cutaneous T-cell lymphoma	Rare, but worth remembering in long-standing patches that never fit the picture and never respond. Needs a biopsy.

Common questions

Can psoriasis be cured?

No. It can be brought to clear or near-clear skin and held there for long periods, sometimes years. It is a long-term condition with a tendency to flare, and treatment is about control rather than cure. Being told this honestly at the start avoids a cycle of disappointment and clinic-hopping.

Is it contagious?

Not at all. It is an immune-mediated condition in which skin cells are produced far faster than normal. Nobody can catch it from you, including by sharing a towel, a bed or a swimming pool.

Why do my joints ache?

Up to a third of people with psoriasis develop psoriatic arthritis. Persistent joint pain and morning stiffness should be mentioned at your consultation, because early treatment prevents permanent joint damage and it changes which medication is chosen.

Are steroid creams safe to keep using?

In courses, under guidance, yes. Used continuously on the same area for months they thin the skin and the condition rebounds harder when stopped. This is why plans alternate steroids with vitamin D analogues and other agents rather than relying on one cream indefinitely.

What triggers a flare?

Throat infections, stress, smoking, alcohol, skin injury, cold dry weather, and certain medicines including some blood pressure tablets and lithium. Abruptly stopping oral steroids can cause a severe flare, which is one reason oral steroids are generally avoided in psoriasis.

This page is general information and does not replace a consultation. Whether any treatment described here is right for you depends on examination, history and other medicines, and that assessment needs a doctor.