·	Plaque psoriasis.The patches most commonly seen are called plaques. They especially affect the back of the elbows and the front of the knees and the back.

·	Guttate psoriasis is many small patches of psoriasis, all over the body, and often happens after a throat infection.

·	Flexural psoriasis causes red, shiny areas in skin folds eg under breasts, between buttocks etc.

·	Pustular psoriasis. Smaller, circular patches, filled with pus, appear on the palms of the hands and soles of the feet. This can sometimes cause a fever, and may need treatment with an antibiotic.

·	Scalp psoriasis. Scaling and flakes of the scalp, often particularly affecting the hair margins.

·	A serious, but rare, complication of psoriasis is erythroderma, where large areas of the skin become hot, red, and dry. This is one of the few emergencies involving skin conditions. If you suffer from this your doctor will admit you to hospital.

·	The joints can be affected by a form of arthritis (Psoriatic arthropathy). This can affect any joint, but often it is only one joint, that becomes inflamed, at a time.

·	One or more of your finger or toe nails may develop little pits as on a thimble, or may become generally more opaque and thickened (nail dystrophy).

·	The eyes may become inflamed (uveitis).

·	Often a patch will start where the skin has been scratched or injured (Köbner phenomenon).

·	A throat infection.

·	Certain medicines or drugs.

·	Moisturising creams and ointments. Used to moisturise dry skin, and also as a substitute for soap when washing the skin.

·	Oils for the bath. Some of these contain tar or antiseptics, which can add other benefits in addition to the moisturising effect.

·	The mainstay of treatment has for years been creams, ointments, lotions and shampoos based on tar. These help cut down scaling of the skin and also have an anti-inflammatory effect. The main worry is their smell!

·	Preparations to be applied, based on Vitamin D (eg Calcipotriol and Tacalcitol) have been found to be very effective, and are probably becoming the first choice with patients and doctors alike.

·	Applications based on salicylic acid (which was originally developed from willow bark, and is related to aspirin) are helpful at removing thick layers of over-grown skin and scales.

·

Sun shine has been known, for years, to help. A development of that, especially as dermatologists are always very suspicious of the sun, is the controlled use of ultraviolet radiation often given with a medication (a psoralen) to prime the skin. (PUVA, Psoralens with long wave ultraviolet radiation.)

·	Stronger medications - prescribed only by a dermatologist, and carefully monitored - are occasionally used and can be very helpful. eg Methotrexate.

·	Mild steroid creams and ointments, used for short periods, for psoriasis affecting the face or body folds. (Stronger preparations and steroids by mouth are sometimes used, but this should be under specialist supervision.)