What is Psoriasis?

Psoriasis (sore-EYE-ah-sis) is a medical condition that occurs when skin cells grow too quickly. Faulty signals in the immune system cause new skin cells to form in days rather than weeks. The body does not shed these excess skin cells, so the cells pile up on the surface of the skin and lesions form.

What are the signs and symptoms? The lesions vary in appearance with the type of psoriasis. There are five types of psoriasis: Plaque, guttate, pustular, inverse, and erythrodermic. About 80% of people living with psoriasis have plaque (plak) psoriasis, also called psoriasis vulgaris. Plaque psoriasis causes patches of thick, scaly skin that may be white, silvery, or red. Called plaques (plax), these patches can develop anywhere on the skin. The most common areas to find plaques are the elbows, knees, lower back, and scalp.

Psoriasis also can affect the nails. About 50% of people who develop psoriasis see changes in their fingernails and/or toenails. If the nails begin to pull away from the nail bed or develop pitting, ridges, or a yellowish-orange color, this could be a sign of psoriatic (sore-EE-at-ic) arthritis. Without treatment, psoriatic arthritis can progress and become debilitating. It is important to see a dermatologist if nail changes begin or joint pain develops. Early treatment can prevent joint deterioration.

What causes psoriasis? Psoriasis is not contagious. You cannot get psoriasis from touching someone who has psoriasis, swimming in the same pool, or even intimate contact. Psoriasis is much more complex.

So complex, in fact, scientists are still studying what happens when psoriasis develops. We know that the persons immune system and genes play key roles. In studying the immune system, scientists discovered that when a person has psoriasis, the T cells (a type of white blood cell that fights unwanted invaders such as bacteria and viruses) mistakenly trigger a reaction in the skin cells. This is why you may hear psoriasis referred to as a T cell-mediated disease.

This reaction activates a series of events, causing new skin cells to form in days rather than weeks. The reason T cells trigger this reaction seems to lie in our DNA. People who develop psoriasis inherit genes that cause psoriasis. Unlike some autoimmune conditions, it appears that many genes are involved in psoriasis.

Scientists are still trying to identify all of the genes involved. One of the genes that has been identified is called PSORS1 (SORE-ESS-1). This is one of several genes that regulates how the immune system fights infection.

Scientists also have learned that not everyone who inherits genes for psoriasis gets psoriasis. For psoriasis to appear, it seems that a person must inherit the right mix of genes and be exposed to a trigger. Some common triggers are a stressful life event, skin injury, and having strep throat. Many people say that that their psoriasis first appeared after experiencing one of these. Triggers are not universal. What triggers psoriasis in one person may not cause psoriasis to develop in another.

Who gets psoriasis? People worldwide develop psoriasis. In the United States, nearly 7.5 million people have psoriasis and about 150,000 new cases are diagnosed each year. Studies indicate that psoriasis develops about equally in males and females. Research also shows that Caucasians develop psoriasis more frequently than other races. A study conducted in the United States found the prevalence was 2.5% in Caucasians and 1.3% in African Americans.

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What Is Psoriasis?