THE FACTS

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.

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.