If you have the skin condition psoriasis, there’s a chance you could also develop psoriatic arthritis. Up to 30% of psoriasis patients will eventually develop psoriatic arthritis, which causes pain, swelling, and stiffness in the joints. The condition usually appears between the ages of 30 and 50 (although it can also start in childhood), and both men and women are equally at risk.

Both psoriasis and psoriatic arthritis are autoimmune diseases, meaning they result when your immune system attacks your body, triggering inflammation. In the case of psoriasis, the immune system attack affects the skin, resulting in raised red, white, or silvery patches. With psoriatic arthritis, the immune system attacks the joints, usually those in the fingers, toes, ankles, knees, wrists, or even the neck and spine.

Many psoriatic arthritis symptoms are similar to those of other forms of arthritis, which can make the condition difficult to diagnose. Like osteoarthritis, psoriatic arthritis can cause painful joints. But osteoarthritis pain usually is a result of cartilage on the joints wearing down and rubbing against each other. Psoriatic arthritis is caused by inflammation in and around the joint and is sometimes mistaken for rheumatoid arthritis, another autoimmune disease with similar symptoms.

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Experts are still trying to figure out what, exactly, causes psoriatic arthritis.

“It probably does have some sort of genetic underpinning,” says Kevin McKown, MD, head of rheumatology at the University of Wisconsin School of Medicine and Public Health, adding that environmental factors usually also play a role.

Having psoriasis is obviously the main risk factor for developing psoriatic arthritis, although it is possible to have psoriatic arthritis without skin psoriasis. Being obese may also increase your risk.

“Some of that may be that adipose [fat] tissue promotes inflammation,” says Dr. McKown. 

Once psoriatic arthritis is identified—usually by looking at a patient’s medical history and X-rays—it’s important for patients to begin treatment right away, since the condition can lead to permanent joint damage over time. Psoriatic arthritis can also raise your risk of other health conditions, such as cardiovascular disease and depression

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Mild psoriatic arthritis may benefit from simple lifestyle changes (for example, moderate exercise) and over-the-counter nonsteroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen (Mortrin and Advil) and naproxen (Aleve). More severe cases usually require stronger drugs, such as disease-modifying antirheumatic drugs (DMARDs) and biologic therapy.

Dr. McKown explains that some studies have shown that controlling inflammation in rheumatoid arthritis helps a person live longer and with fewer cardiac events—and this could offer hope for psoriatic arthritis patients, as well.

"We don’t know yet if this is the case for psoriatic arthritis, but it makes sense," he says.