Psoriasis is a chronic skin disease characterized by red patches on the skin, often accompanied by silvery-white scales of dead skin cells. It is not contagious.

Psoriasis is believed to be an autoimmune disease, meaning the body's defense system attacks healthy cells in the body. This creates skin cells that mature and die in less than a week, which is extremely rapid considering normal skill cells mature and replace dead ones usually in a month's time.

The buildup of dead cells on the skin's surface is called plaque. While these can occur anywhere on the body, they are more common in the following areas:

The National Psoriasis Foundation estimates that as many as 7.5 million Americans and 125 million people worldwide (about 2.2 percent of the population) have psoriasis, making it the most prevalent autoimmune disease in the world.

While psoriasis affects the skin, it goes beyond a cosmetic problem. The exterior symptoms of psoriasis can affect a person's self-esteem and personal image, which can create problems in their everyday lives such as anxiety and alienation.

There are several different types of psoriasis, distinguished by 1) the affected area of the body and 2) the type of patches. They include:

This type involves plaques on the scalp that typically can be confused as dandruff. About half of all people with any type of psoriasis also have scalp psoriasis.

Found anywhere on the body, plaque psoriasis is the most common form of psoriasis. Small red bumps spread and dead skin cells easily flake from those areas.

This type of psoriasis involves smooth inflamed lesions in areas where the skin folds or flexes, such as the armpits, groin, or under the breast.

This kind causes severe disruption to the body's chemical balance, affecting the majority of the body, and causes symptoms such as severe scaling, pain, and itching to the point where the skin looks as though it has been burned. It can also cause severe illness.

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Psoriasis: Symptoms, Pictures, Causes, and Treatments