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Psoriasis is not contagious and it is difficult to say what triggers it.

A family history of psoriasis is the greatest known risk factor.

Smoking, excessive drinking and stress are known to worsen symptoms.

Psoriasis is a chronic inflammotory skin disease

Psoriasis is a chronic inflammatory disorder of the skin, the body’s largest organ and the first line of protection from the environment. Although the direct cause of psoriasis is currently unknown, it results in skin cells growing abnormally fast, causing the skin to shed every three to four days.

An autoimmune disease

There are five types of psoriasis: plaque, guttate, inverse, pustular and erythrodermic. The most common form, plaque psoriasis, is characterized by inflamed, scaly, red, itchy patches called psoriatic plaques. It is a fluctuating condition with recurrent episodes of variable severity. About 10% to 20% of psoriasis patients develop psoriatic arthritis, an inflammatory joint disease.

Psoriasis and psoriatic arthritis are considered to be autoimmune diseases, in which the immune system attacks the body’s own tissues.

Most common among people of European ancestry

Psoriasis is most common among people of European ancestry (with a prevalence of 2% to 3%). Women have a slightly higher risk of developing psoriasis according to some studies. Psoriasis is estimated to affect 5 to 7 million people in the US.

Genetics contribute to the development of Psoriasis

There are eight genetic variants known to increase the risk of developing psoriasis; located on chromosomes 1, 5, 6, and 12. Of these the variant in the HLA-C gene contributes by far the strongest effect to the risk of developing psoriasis in most if not all populations tested.

deCODEme can calculate your genetic risk

The deCODEme Complete Scan identifies the eight genetic variants listed above and provides interpretation of their associated risk for developing psoriasis in individuals of European descent.

In East Asians, the deCODEme Complete Scan currently calculates genetic risk associated with three variants; on chromosomes 1, 5, and the HLA-C variant on chromosome 6. Currently no risk data are available for people of other ethnicities for the variants listed above.

Risk factors

Family history is the greatest risk factor

A family history of psoriasis is the greatest risk factor. In a study of identical twins, 70% of twins who had psoriasis had a twin who also had psoriasis. Studying identical twins for concordance (both twins having the same disease) is generally a good measure of genetic contribution since their inherited genetic material (DNA) is identical. A 70% concordance rate is considered to be very high for a condition of complex inheritance such as psoriasis.

A genetic connection exists between psoriasis and the immune system

Psoriasis appears to involve the immune system. Therefore, it is not surprising that the gene most strongly and consistently associated with psoriasis is a gene important in immune response. HLA-C, specifically HLA-Cw6, is associated with psoriasis in most, if not all, populations tested. Commonly, over 60% of psoriasis patients carry one or more copies of the Cw6 variant of HLA-C compared with 8% to 12% of those who do not have psoriasis.

On average, psoriasis patients who have the Cw6 variant tend to develop the disease a few years earlier and can have more severe progression of the disease compared with psoriasis patients who do not have the Cw6 variant. Recently, two other genes, IL-12beta and IL-23R, have been associated with psoriasis, but they do not seem to play as important a role as HLA-Cw6 in their contribution to the risk of developing the disease.

Prevention and treatment

Psoriasis is not contagious. No preventive measures are known to be effective, since not much is known about what triggers the onset of psoriasis. Usually, no obvious trigger is found. Some studies have indicated that an infection (most often a streptococcal infection or "strep throat") can stimulate or perhaps over-stimulate the immune system into a state of self-attack. Several other factors including smoking, excessive drinking, and stress are known to worsen or exacerbate symptoms.

Effective treatments are available

At the present time, there is no cure for psoriasis. There are many treatments available depending on disease severity, ranging from skin moisturizers to immunosuppressive medications. The goal of treatment is to reduce inflammation and slow the rapid growth and shedding of skin cells.

More information

You can find out more information about psoriasis by talking with a doctor and visiting these Web sites:
American Academy of Family Physicians
MedlinePlus Article on Psoriasis
National Institute of Arthritis and Musculoskeletal and Skin Diseases
The National Psoriasis Foundation

This content was last reviewed on February 23, 2011.

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