Psoriasis causes skin scaling and inflammation. It may or may not cause itching. There are several types of psoriasis:
Plaque psoriasis. In plaque psoriasis, there are rounded or oval patches (plaques) of affected skin. These are usually red and covered with a thick silvery scale. The plaques often occur on the elbows, knees, scalp or near the buttocks. They may also appear on the trunk, arms and legs.
Inverse psoriasis. Inverse psoriasis is a plaque type of psoriasis that tends to affect skin creases. Creases in the underarm, groin, buttocks, genital areas or under the breast are particularly affected. The red patches may be moist rather than scaling.
Pustular psoriasis. The skin patches are studded with pimples or pustules.
Guttate psoriasis. In guttate psoriasis, many small, red, scaly patches develop suddenly and simultaneously. Guttate psoriasis often occurs in a young person who has recently had strep throat or a viral upper respiratory infection.
About half of people with skin symptoms of psoriasis also have abnormal fingernails. Their nails are often thick and have small indentations, called pitting.
A type of arthritis called psoriatic arthritis affects some people with psoriasis. Psoriatic arthritis may occur before skin changes appear.