The Good News on Allergies: They Might Protect Against Cancer

Allergies are a pain, but a new study suggests that they may actually be helpful. The immune systems of people with contact allergies may be primed to protect against some forms of cancer, including breast and non-melanoma skin cancer, according to a new study.

Scientists focused on nearly 17,000 Danish adults who were tested for contact allergies, when an allergic reaction occurs due to direct contact with chemicals such as acetone and common metals, including nickel and cobalt. People with contact allergies usually develop a rash on the area that touched the allergen within 24 hours.

About one-third of the study participants tested positive for at least one contact allergy, with women more likely to test positive (41 percent) than men (26 percent). The participants were tested between 1984 and 2008.

Scientists estimate about 20 percent of the general Danish population has contact allergies; In the United States, 30 million to 45 million people have contact allergies —or more than 10 percent of the U.S. population, according to an April 2011 Harvard study.

Researchers at the National Allergy Research Centre at Copenhagen University Hospital Gentofte in Hellerup, Denmark, examined cancer cases among the study participants over the long term. The findings showed that men and women with contact allergies had significantly lower rates of breast cancer and non-melanoma skin cancer.

The study also showed that women with contact allergies had lower rates of brain cancer compared with women without contact allergies, though that was not statistically significant. However, researchers found that both men and women with contact allergies had higher rates of bladder cancer, which "could be due to accumulations of chemical metabolites in the bladder," according to the study.

The lower rates of brain, breast and non-melanoma skin cancer among those with contact allergies may be the result of how their immune systems function. According to researchers, the findings support the immunosurveillance hypothesis — the theory that individuals with so-called hyperimmunity have the side effect of allergies. This hyperimmunity is what may protect against some cancers.

The researchers caution that the results show a correlation between contact allergies and lowered rates of some cancers, but do not mean that one caused the other.

The study was published on July 12 in the journal BMJ Open.

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