People who get skin rashes when exposed to certain metals or chemicals may be less likely to develop some types of cancer, according to a study published yesterday (July 11) in the journal BMJ Open.
Earlier epidemiological studies comparing medical histories and allergies (usually self-reported) revealed a lower incidence of certain cancers in allergic people than in those without allergies. The studies supported the hypothesis that an overactive immune system—which causes adverse reactions to dust, cats, and pollen—also provides better protection against cancer, killing cells with cancerous potential before they become problematic. (Read our Feature on this topic, Immune System Vs. Cancer.)
However, there are differences in how the immune system is activated in different allergies. An association between lower cancer rates and immediate allergies like hay fever and asthma might not hold true for delayed contact-allergies like hives and rashes. Therefore, researchers looked at Danish hospital registries, analyzing nearly 17,000 adults with contact allergies over a period of 24 years. They found that the incidence of breast cancer and some skin cancers was lower in these patients, suggesting that contact allergies are indeed linked to cancer risk. Surprisingly, however, bladder cancer was more common among allergic patients. But because the study was retrospective, it does not prove any of the apparent relationships, and more work will be needed to confirm the links exist and determine their root causes.