Psoriasis is a chronic (long-lasting) skin disease of scaling and inflammation that affects greater than 3 percent of the United States population, or more than 5 million adults. Although the disease occurs in all age groups, it primarily affects adults. It appears about equally in males and females.
Psoriasis occurs when skin cells quickly rise from their origin below the surface of the skin and pile up on the surface before they have a chance to mature. Usually this movement (also called turnover) takes about a month, but in psoriasis it may occur in only a few days.
In its typical form, psoriasis results in patches of thick, red (inflamed) skin covered with silvery scales. These patches, which are sometimes referred to as plaques, usually itch or feel sore. They most often occur on the elbows, knees, other parts of the legs, scalp, lower back, face, palms, and soles of the feet, but they can occur on skin anywhere on the body. The disease may also affect the fingernails, the toenails, and the soft tissues of the genitals, and inside the mouth. Although it is not unusual for the skin around affected joints to crack, about 30 percent of those with psoriasis experience joint inflammation that produces symptoms of arthritis. This condition is called psoriatic arthritis.
What Causes Psoriasis?
Psoriasis is a skin disorder driven by the immune system, especially involving a type of white blood cell called a T cell. Normally, T cells help protect the body against infection and disease. In the case of psoriasis, T cells are put into action by mistake and become so active that they trigger other immune responses, which lead to inflammation and to rapid turnover of skin cells.
In many cases, there is a family history of psoriasis.
There are several forms of psoriasis. Some of these include:
Plaque psoriasis: Skin lesions are red at the base and covered by silvery scales.
Guttate psoriasis: Small, drop-shaped lesions appear on the trunk, limbs, and scalp. Guttate psoriasis is most often triggered by upper respiratory infections (for example, a sore throat caused by streptococcal bacteria).
Pustular psoriasis: Blisters of noninfectious pus appear on the skin. Attacks of pustular psoriasis may be triggered by medications, infections, stress, or exposure to certain chemicals.
Inverse psoriasis: Smooth, red patches occur in the folds of the skin near the genitals, under the breasts, or in the armpits. The symptoms may be worsened by friction and sweating.
Erythrodermic psoriasis: Widespread reddening and scaling of the skin may be a reaction to severe sunburn or to taking corticosteroids (cortisone) or other medications. It can also be caused by a prolonged period of increased activity of psoriasis that is poorly controlled.
Another condition in which people may experience psoriasis is psoriatic arthritis. This is a form of arthritis that produces the joint inflammation common in arthritis and the lesions common in psoriasis. The joint inflammation and the skin lesions don’t necessarily have to occur at the same time.
*Information from National Institutes of Health (NIH)