Medical Dermatology

Psoriasis

Psoriasis is a chronic immune-mediated condition producing well-defined, scaly plaques. It is not contagious, it is not caused by poor hygiene, and although it cannot be cured, treatment has advanced considerably.

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At a glance

What it is: An immune-mediated genetic skin disease in which skin cells proliferate excessively against a background of inflammation.
Who it affects: Around 2–4% of people. It can begin at any age, with peaks around 15–25 and 50–60 years. About one-third have an affected family member.
Common sites: Scalp, elbows, knees and lower back — though any area of skin can be involved, including nails and skin folds.
Beyond the skin: Psoriatic arthritis affects a substantial minority. Associations with metabolic and cardiovascular health are also recognised.
Treatment: Topical therapy, phototherapy, systemic medication and biologics, matched to severity and impact.

Understanding the condition

What is psoriasis?

In psoriasis the immune system drives skin cells to multiply far faster than normal. Instead of maturing and shedding invisibly, the cells accumulate on the surface, producing the characteristic raised plaque with adherent silvery-white scale. Beneath the scale, the skin is inflamed.

Plaques are usually symmetrically distributed with clearly defined edges — a feature that helps distinguish psoriasis from eczema. In skin folds the scale is often absent and the surface appears shiny and moist instead. Itch is usually mild, though it can be severe, and painful fissures may develop on the palms and soles.

This is an immune-mediated genetic disease involving inflammatory signalling molecules such as TNF-alpha, IL-17 and IL-23. Identifying these pathways is precisely what has made modern biologic treatments possible.

The Koebner phenomenonNew psoriatic plaques can appear at sites of skin injury — a scratch, a burn, a surgical scar or persistent friction. This is worth knowing, because it explains why protecting the skin from trauma is part of good management.

Recognising the pattern

Types of psoriasis

Several distinct patterns exist, and more than one can occur in the same person over time.

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Plaque psoriasis

By far the most common form.

Well-defined raised plaques with silvery scale
Typically scalp, elbows, knees and lower back
Persistent without treatment
In deeper skin tones plaques may look violet or dark brown with grey scale

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Guttate psoriasis

Small drop-like lesions, often after infection.

Numerous small scaly spots, mainly on the trunk and limbs
Classically follows a streptococcal throat infection
More common in children and younger adults
May resolve, or may evolve into plaque psoriasis

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Flexural (inverse)

Affecting the skin folds.

Armpits, groin, under the breasts and between the buttocks
Smooth, shiny and red rather than scaly
Can be uncomfortable and is easily mistaken for a fungal infection

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Nail psoriasis

Frequently accompanies skin disease.

Small pits in the nail surface
Discolouration and changes in nail growth
Separation of the nail from the nail bed
Thickening or crumbling in more severe cases

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Palmoplantar

Palms and soles.

Thickened, scaly skin on the palms and soles
Painful cracks and fissures
Can significantly affect the use of hands and walking

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Pustular & erythrodermic

Uncommon but important.

Sterile pustules, localised or widespread
Erythrodermic psoriasis affects most of the skin surface
These forms can be serious and require prompt medical assessment

How psoriasis is assessed

Severity and impact

Treatment decisions are guided by more than the area of skin involved. How much the condition affects daily life carries real weight.

Consideration	What it means
Extent	The body surface area affected, and formal scoring where appropriate
Site	Hands, feet, face, scalp and genitals affect life disproportionately even when the area is small
Impact	Effect on sleep, work, relationships and mood — a legitimate treatment consideration
Comorbidity	Psoriatic arthritis, and associations with metabolic and cardiovascular health
Circumstances	Age, general health, other medication, and pregnancy plans

A limited area of psoriasis on the hands or face may justify more active treatment than a larger area elsewhere.

Treatment

How psoriasis is treated

Treatment is chosen according to the pattern, severity, impact and individual circumstances. Several approaches may be combined or rotated.

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Topical treatment

Suitable for limited disease and used alongside other therapy.

Topical corticosteroids
Vitamin D analogues
Calcineurin inhibitors for delicate sites
Coal tar preparations
Emollients to reduce scale and cracking

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Phototherapy

Controlled ultraviolet treatment delivered under supervision.

Useful for more widespread plaque or guttate disease
Requires a course of regular sessions
Distinct from sunbeds, which are not a treatment

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Systemic & biologic

For moderate to severe disease, or where topical therapy is insufficient.

Methotrexate, ciclosporin or oral retinoids
Biologic therapies targeting TNF-alpha, IL-17 or IL-23
Require monitoring and specialist supervision
Often also benefit associated psoriatic arthritis

Everyday management

Living with psoriasis

General measures do not replace treatment, but they reduce flares and improve how the skin feels.

Helpful

Use emollients regularly to soften scale and reduce cracking
Treat streptococcal throat infections promptly
Protect skin from injury, friction and sunburn
Address stress where you can — it is a genuine trigger for many
Tell your doctor about joint pain, stiffness or swelling
Attend to general health: weight, blood pressure and cardiovascular risk

Unhelpful

Scratching or picking off scale, which can provoke new plaques
Smoking, which aggravates psoriasis
Excess alcohol
Sunbeds as a substitute for medical phototherapy
Stopping treatment abruptly without advice
Assuming nothing more can be done — options have expanded considerably

Seeking help

When to see a dermatologist

Consider a specialist assessment if:

Psoriasis is not responding to treatments already tried
Plaques affect the scalp, face, hands, feet or genitals
Nails are involved
You have joint pain, stiffness or swelling
The condition is affecting your mood, confidence or daily life
You are uncertain whether the rash is psoriasis

Seek prompt medical attention ifpsoriasis becomes suddenly widespread and inflamed across most of the body, or if you develop widespread pustules with feeling unwell or fever. These uncommon presentations need urgent assessment.

Dr Chen Qiping

Consultant Dermatologist · MBBS, MRCP (UK), M.Sc, FAMS (Dermatology)

Dr Chen practises general adult and paediatric dermatology, including psoriasis, alongside surgical, laser and cosmetic dermatology. Consultations are available in English and Mandarin.

Full profile →

Common questions

Psoriasis — frequently asked questions

Is psoriasis contagious?

No. Psoriasis cannot be passed from person to person by any form of contact. It is an immune-mediated condition with a strong genetic component — about one-third of people with psoriasis have a family member who is also affected.

Is psoriasis curable?

There is currently no cure, and no single treatment works for everyone. However, psoriasis is very treatable. It tends to persist lifelong while fluctuating in extent and severity, and the realistic aim is sustained clearance or near-clearance of the skin. Several treatments may need to be tried, and they are often used in combination or in rotation.

What is the difference between psoriasis and eczema?

They can look similar but differ in important ways. Psoriasis typically produces sharply demarcated, thickened plaques with silvery-white scale, favouring the scalp, elbows, knees and lower back, and itch is often mild. Eczema tends to be less well defined, favours the skin creases, and itch is usually the dominant symptom. Nail changes and a family history are also more suggestive of psoriasis. Where the distinction is unclear, examination and occasionally a biopsy will settle it.

Can psoriasis affect my joints?

Yes. Psoriatic arthritis develops in a proportion of people with psoriasis — estimates commonly range from about 10% to 30%. It causes joint pain, stiffness and swelling, and skin disease usually precedes it. Tell your doctor about any persistent joint symptoms, because early recognition matters.

Why do my plaques leave marks after they clear?

When psoriatic plaques resolve they commonly leave brown or pale marks — post-inflammatory hyperpigmentation or hypopigmentation. These are more noticeable in deeper skin tones and can be mistaken for active disease or scarring. They are neither, and can be expected to fade over several months.

What makes psoriasis flare?

Recognised aggravating factors include streptococcal throat infection, skin injury (new plaques can appear at sites of trauma — the Koebner phenomenon), stress, smoking, and certain medications including lithium, beta-blockers and antimalarials. Identifying your own pattern is useful, though flares sometimes occur without explanation.

References

DermNet. Psoriasis and Treatment of psoriasis. dermnetnz.org
MSD Manual Professional Edition. Psoriasis. Reviewed by Shinjita Das, MD MPH. msdmanuals.com
Mayo Clinic. Types of psoriasis. mayoclinic.org

Page last reviewed: 28 July 2026.

Important — This page is general information about a skin condition and is not medical advice. It cannot take the place of an individual consultation, examination and diagnosis. Treatment options, their suitability and their possible side effects should be discussed with a qualified doctor who has assessed your skin. Individual results vary. If you have concerns about your skin, please arrange a consultation.

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