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The Claim: Having allergies reduces the risk of getting cancer.

By Anahad O’Connor

Allergies are generally considered more of a nuisance than a blessing. But for some people there may be a silver lining.

Researchers have long speculated that one of the benefits of having allergies is a vigilant immune system, which not only overreacts to common triggers, like pollen and dander, but also protects against serious threats like nascent cancer cells. Numerous studies dating back at least two decades have explored the idea of a link. Most have found that compared with the general population, people with common allergies like hay fever, asthma and eczema do have a slightly decreased risk of some cancers, though it is not clear why.

In a study published online this month in the journal BMJ Open, Danish researchers tracked nearly 17,000 adults who were tested from 1984 to 2008 for contact allergies—that is, contact with metals, poison ivy, hair dyes or other chemicals caused them to develop skin irritation. After monitoring the subjects’ long-term health and cross-checking their records against a cancer registry, the scientists found that people with contact skin allergies had lower rates of breast and skin cancer.

The researchers also found an association between contact allergies and increased risk for bladder cancer, but they suspected it was connected to the use of hair dye, which has been linked to bladder cancer in previous studies.

Skin allergies prompt the production of immune system t cells, which can destroy cancer cells. Any protective effect may stem from the immune system going into “overdrive,” said dr. Clifford w. Bassett, a New York City allergist and fellow of the American college of Allergy, Asthma and Immunology.

THE BOTTOM LINE

Studies suggest having allergies may lower the risk of some cancers, but more research is needed.