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What Is Psoriasis?

What Is Psoriasis?

Psoriasis is a common and chronic skin disease. A person with psoriasis generally has patches of raised red skin with thick silvery scales. The affected skin may be red and scaly or rarely have pustules, depending on the type of psoriasis the individual has.

Psoriasis is usually found on the elbows, knees, and scalp but can often affect the legs, trunk, and nails. Psoriasis may be found on any part of the skin.

Plaque psoriasis on the elbow. Plaque psoriasis is the most common type of psoriasis. Image courtesy of Hon Pak, MD.

Psoriasis is not an infection and therefore is not contagious. Touching the affected skin and then touching someone else will not transmit psoriasis. However, the red scaly skin can become infected, especially when there are splits in the skin.

The immune system plays a key role in psoriasis. In psoriasis, a certain subset of T lymphocytes (a type of white blood cell) abnormally trigger inflammation in the skin as well as other parts of the body. These T cells produce chemicals that cause skin cells to multiply abnormally quickly, as well as producing changes in small skin blood vessel which result ultimately an elevated scaling plaque of psoriasis.

Plaque psoriasis on the back. Image courtesy of Hon Pak, MD.

Psoriasis can be inherited. Some people carry genes that make them more likely to develop psoriasis. Just because a person has genes that would make him more likely to have psoriasis doesn't mean he will have the disease. About one-third of people with psoriasis have at least one family member with the disease. Certain factors trigger psoriasis to flare up in those who have the genes.

Environmental factors such as smoking, exposure to sun, and alcoholism may affect how often psoriasis occurs and how long the flare-ups last. Injury to the skin has been known to trigger psoriasis. For example, a skin infection, skin inflammation, or even excessive scratching can trigger psoriasis. A number of medications have been shown to aggravate psoriasis.

Psoriasis flare-ups can last for weeks or months. Psoriasis can go away for a time and then returns.

Plaque psoriasis is the most common type of psoriasis and is characterized by red skin covered with silvery scales and inflammation. Patches of circular- or oval-shaped red plaques that itch or burn are typical of plaque psoriasis.

Plaque psoriasis with fissures, which are splits in the skin. Fissures usually occur where the skin bends (joints). The skin may bleed and is more susceptible to infection. Image courtesy of Hon Pak, MD.

Approximately 1%-2% of people in the United States, or about 5.5 million, have plaque psoriasis. Up to 10% of people with plaque psoriasis also have psoriatic arthritis. Individuals with psoriatic arthritis have inflammation in their joints that could result in permanent joint damage if not treated aggressively. Recent information indicates the most patients with psoriasis are also predisposed to obesity, diabetes, and early cardiovascular diseases. It is now becoming apparent that psoriasis is not just a skin disease but can have widespread systemic effects.


Guttate psoriasis. Red drop-like lesions are found on the skin. Image courtesy of Hon Pak, MD.

Sometimes plaque psoriasis can evolve into more severe disease, such as pustular or erythrodermic psoriasis. In pustular psoriasis, the red areas on the skin contain blisters with pus. In erythrodermic psoriasis, a wide area of red and scaling skin is typical, and it may be itchy and painful.

Pustular psoriasis. Note the clearly defined, raised bumps on the skin that are filled with pus (pustules). The skin under and around these bumps is reddish. Image courtesy of Hon Pak, MD.

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Psoriasis is a chronic, noncontagious, multisystem, inflammatory disorder.

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