Contact allergies are delayed reactions to metals like nickel or cobalt or to chemicals, such as those found in plants such as poison ivy and poison oak, perfumes, and hair dyes.
Earlier research suggests that people who suffer from other types of allergies may have a lower risk for certain cancers, but the new study is among the first to look specifically at contact skin allergies.
The findings do not prove that contact allergies have a direct impact on cancer risk, but they do suggest an association, researcher Kaare Engkilde, PhD, of Denmark’s National Allergy Research Center, tells WebMD.
“These allergies haven’t really gotten much attention in research, but it looks like they may have a more systemic effect than we had previously thought,” he says.
Using Danish health registries, Engkilde and his research team were able to follow nearly 17,000 adults in that country who were tested for contact skin allergies between 1984 and 2008.
About one in three (35%) had positive reactions to at least one allergen. Women were more likely than men to have a contact allergy, with 41% testing positive, compared to 26% of men.
Allergic People Had Fewer Breast, Skin Cancers
Using a national cancer registry, the researchers were able to determine the study participants’ long-term risk for 15 different malignancies.
When the researchers compared the allergy and cancer data sets, they found that people with contact skin allergies had lower rates of breast and non-melanoma skin cancers.
Women with skin allergies had slightly lower rates of brain cancer, but this was not seen in men.
People with contact skin allergies had higher rates of bladder cancer, which could explain the suspected link between hair dyes and the cancer, Engkilde says.
“This is speculative, but it could be that higher levels of chemical metabolites that accumulate in the blood could cause bladder cancer,” he says.
Unlike other common allergies, such as those to pollen and home dust mites, contact skin allergies stimulate the production of natural killer T (NKT) cells.
Engkilde says these NKT cells may target and kill nascent cancer cells, but he adds that more research is needed to prove the connection.
William Chambers, PhD, of the American Cancer Society (ACS) tells WebMD that the notion that an activated immune system can protect against cancer was first raised nearly 100 years ago.
Chambers is director of clinical cancer research and immunology for ACS.
“There is now wide acceptance among immunologists that cell-mediated immunity plays a role in certain cancers,” he says.
He adds that a better understanding of the association could have implications for the prevention and treatment of malignancy.