Last updated: Sep 26, 2016

Psoriasis is a chronic autoimmune disease that affects the skin and, in some cases, the joints. No one knows for sure what causes the condition, which is believed to affect as many as 7.5 million Americans. Researchers believe that a combination of genetic and environmental factors set off the immune system, which in turn sends faulty signals to overproduce new skin cells. Those extra cells usually build up into red, crusty patches on the body, which aren't contagious but can itch and become painful.

About one-third of those with the condition have a family history of the disease. If you are a first-degree relative of somebody who has psoriasis—that means if your brother, sister, or parent has psoriasis—you have an elevated risk of developing the disease. Other than that, there's no way to predict who's going to get psoriasis and who's not.

The disease is diagnosed most often in early adulthood, between the ages of 20 and 35. Triggers such as infections or stress can bring on psoriasis in those who are genetically predisposed to it.

Kelly M. Cordoro, MD, associate professor of dermatology at the University of California, San Francisco, once had a 22-year-old male patient whose mother had psoriasis. Within two weeks of getting strep throat—, a bacterial infection that can trigger psoriasis—, he developed a type of psoriasis known as guttate psoriasis.

Reducing the likelihood and severity of psoriasis

If you're genetically at greater risk for psoriasis, avoiding or minimizing triggers such as alcohol, stress, and skin injuries may decrease your likelihood of acquiring the disease.

Drugs——including antimalarial medications, lithium, and some heart medications——can trigger or worsen psoriasis, so make sure to tell your physician you have psoriasis when receiving new medication. (Visit the National Psoriasis Foundation for a list of medications that can trigger psoriasis.)

If you already have psoriasis, wearing protective clothing in cold, dry weather and moisturizing well can help keep flares at bay.

In addition, see a dermatologist that has experience treating psoriasis and stick with the treatment he or she prescribes. Maintaining a healthy lifestyle by keeping your body at a good weight, getting consistent sleep, and avoiding smoking and drinking will also help your condition.

Hope for related conditions

Up to 30% percent of people who have psoriasis will develop psoriatic arthritis, an inflammation of the joints similar to rheumatoid arthritis.

People who develop psoriatic arthritis may be more prone to developing other health problems, most notably cardiovascular disease. If someone with psoriasis also has pain or discomfort in their joints or experiences unusual stiffness, it is important to be evaluated for arthritis. Like psoriatic arthritis, psoriasis can increase the risk of developing heart disease. Both psoriasis and cardiovascular disease involve inflammation, but experts are not sure of the exact connection between the two conditions.