What are the different types of psoriasis?
There are different types of psoriasis, although plaque psoriasis (described below) is by far the most common and typical type.
Plaque psoriasis
This is common. The rash is made up of patches on the skin called plaques. The picture shows a typical plaque of psoriasis next to some normal skin.
Each plaque usually looks red with overlying flaky white scales that feel rough. There is usually a sharp border between the edge of a plaque and normal skin. The most common areas affected are over elbows and knees, the scalp, and the lower back. However, plaques may appear anywhere on the skin, but they do not usually occur on the face.
The extent of the rash varies between different people, and can vary from time to time in the same person. Many people have just a few small plaques when their psoriasis flares up. Others have a more widespread rash with large plaques. Sometimes, small plaques that are near to each other merge to form large plaques.
Plaque psoriasis can be itchy, but does not usually cause too much discomfort. Treatment is discussed later.
Scalp psoriasis
This occurs in about half of people affected by plaque psoriasis. It can also occur alone without any other part of the skin being affected. It looks like severe dandruff.
Nail psoriasis
This occurs in about half the people with plaque psoriasis. It may also occur alone without the skin rash. There are pinhead sized pits (small indentations) in the nails. Sometimes, the nail becomes loose on the the nail bed.
Guttate ('drop') psoriasis
This typically occurs following a sore throat which is caused by a bacterium (germ). The plaques of psoriasis are small (less than 1 cm) but occur over many areas of the body. It normally lasts a few weeks, and then fades away. It may never return. But, if you have an episode of guttate psoriasis, you have a higher than usual chance of developing common plaque psoriasis at a later time.
Flexural psoriasis
This occurs on skin in the creases of the skin (flexures) such as in the armpit, groin, under breasts, and in skin folds. The affected skin is red and inflamed. Unlike plaque psoriasis, affected skin is smooth and does not have the rough scaling.
Pustular psoriasis
This is uncommon and mainly affects the palms of the hands and and soles of the feet. In this situation it is sometimes called palmoplantar pustulosis. Affected skin develops crops of pustules which are small fluid filled spots. The pustules of pustular psoriasis do not contain germs (bacteria) and are not infectious. The skin under and around the pustules is usually red and tender. Rarely, a form of pustular psoriasis can affect skin apart from the palms and soles. This more widespread form of pustular psoriasis is a more serious form of psoriasis and needs urgent treatment.
Erythrodermic psoriasis
This is a widespread erythema (redness) of much of the skin surface which is painful. It is rare, but is serious and needs urgent treatment as it can cause excessive protein and fluid loss that can lead to dehydration and severe illness.
Joint problems
About 1 in 10 people with psoriasis also develop inflammation and pains in some joints (arthritis). This is called psoriatic arthritis. Any joint can be affected, but it most commonly affects the joints of the fingers and toes. The cause of this is not clear.
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