It turns out that psoriasis, a chronic skin condition that causes itchy, scaly red patches, is more than skin deep. Over the last decade, researchers discovered that psoriasis is due to a problem not with the skin but with the immune system—and a recent study has linked the condition to lymphoma, which is a cancer of the immune system.

The study, published in the November 2003 issue of the Archives of Dermatology, found that the rate of lymphoma in people with psoriasis was almost three times higher than the rate in people without the skin condition. But it's yet not clear what caused the increase in lymphomas.

Over a 46-month period, researchers examined patients aged 65 and older in the United Kingdom who were seen by a doctor registered with the General Practice Research database. While 2,718 patients had psoriasis, 105,203 did not. Researchers found that there were 122 more lymphomas annually per 100,000 patients among the group with psoriasis, compared with those without psoriasis.

Joel M. Gelfand, MD, the principle investigator and an assistant professor at the University of Pennsylvania in Pittsburgh says larger studies need to be done in determine the reason for the increase.

"People with significant psoriasis may be at risk for immune cancers like lymphoma because they have extra immune activity, which increases the risk of your immune cells going awry," Dr. Gelfand says. "Or some of the treatment that suppresses the immune system could increase risk. Or the increase could be due to a combination of these factors."

Dr. Gelfand emphasizes that the rate of lymphoma among people with psoriasis is still low, but that the risks and benefits of treatments for psoriasis should be weighed carefully.