NEW YORK - People with the skin condition atopic dermatitis may be at greater risk of getting cancer than those without it, new research hints.

But it's unclear whether this increased risk is related to the medication patients take for the condition, or the condition itself, the researchers emphasize.

Atopic dermatitis is a type of eczema, or skin inflammation, that arises from an allergic reaction. It affects roughly 20 percent of children, according to the National Institutes of Health, but often goes away in adulthood. It causes itchy rashes that get crusty and scaly with scratching.

There have been conflicting theories about whether these kinds of frequent rashes that drive the immune system into action would make it more or less likely for someone with atopic dermatitis to develop cancer.

To investigate, Dr. Alejandro Arana, of the Bridgewater, New Jersey-based company Risk Management Resources and colleagues analyzed the medical records of about 4.5 million people in the UK and followed their medical history for an average of almost 7 years.

They report, in the British Journal of Dermatology, that about 1.5 percent of those individuals had atopic dermatitis and just under 3 percent were diagnosed with some kind of cancer during the study period. People in the study with atopic dermatitis were on average 12 to 15 years younger than those without atopic dermatitis.

Overall, people without atopic dermatitis were more likely to get cancer than people with the skin condition. There were 129,272 first cancer cases in people without atopic dermatitis (about 33 cases per 10,000 persons per year) and 700 first cancer cases (about 42 cases per 10,000 persons per year) in those with atopic dermatitis.

But when the investigators took out the effect of age differences and looked within each specific age group, the pattern switched. At every age, the rate of cancer was higher among patients with atopic dermatitis.

That general pattern held when Arana and his colleagues looked specifically at lymphoma, melanoma, and non-melanoma skin cancer. When examined by age group, people with atopic dermatitis were about 1.5 times more likely to be diagnosed with some kind of cancer during the study than people without atopic dermatitis.

But the results don't prove that having atopic dermatitis causes cancer, the investigators emphasize.

"These are difficult studies to do well and sometimes it's difficult to understand what they mean," Dr. David Margolis, a dermatologist at the University of Pennsylvania Health System who was not involved with the study told Reuters Health. Among patients with atopic dermatitis, the overall cancer risk was still low, he emphasized. "I think people just need to put their results in perspective," he said.

"The age specific risk differences seen in this study are small," Arana told Reuters Health in an email, "but doctors should always be aware of recent investigations and take cancer primary prevention measures in (atopic dermatitis) patients."

The findings also don't separate the effect of medication from the effect of the skin condition itself. Typical treatment for atopic dermatitis includes hydrocortisone lotions, wet dressings, and sometimes prescription medications. In 2005, the FDA issued an advisory that two of these medications, Elidel and Protopic, might carry a cancer risk.

The current study was funded by a grant from the pharmaceutical company Novartis, which markets Elidel, and two of its co-authors are Novartis employees.

Arana said that this study should be taken in the larger context of research on the possible link between atopic dermatitis and cancer. "We cannot establish a cause and effect relationship from one study alone," he told Reuters Health. "Each study should be seen as a brick in the wall of knowledge."

"This is another helpful study along the way that might help (give) some clarity in the future," Margolis added.

SOURCE: British Journal of Dermatology, online June 9, 2010.