Contact allergies can protect against a small number of cancers, Danish researchers write.
Men and women was found inverse association between contact allergy and non-melanoma skin cancer, and breast cancer. Women with a contact allergy was found to reverse the trend of brain cancer.
However, the authors have also identified positive associations between contact allergy and bladder cancer.
Inverse associations support the theory of immunological surveillance, in which allergic symptoms - a negative impact hyperimmune, according to a report published in the online edition of «BMJ Open» on July 11.
The reason for these associations remains unclear, and they are not necessarily the result of a causal relationship. "Our study - the research, and it is difficult to make recommendations directly to clinicians based on a single study," - said Dr. Kaare Engkild (National Allergy Research Center, Copenhagen, Denmark).
"I would not recommend the reduction of screening for breast cancer, non-melanoma skin cancer, or cancer of the brain, although the emergence of such associations should lead to further research", - said Dr. Engkild.
Using the registration data, Dr. Engkild and colleagues identified 16 922 patients with dermatitis who underwent tests for contact allergy from November 1984 to December 2008. Of this group, 6065 (35.8%) tested positive for at least 1 allergen, at least in one case. The authors note that the prevalence of contact allergy was higher in women than in men (41.4% vs. 26.1%).
The data were linked with the Danish Cancer Registry, and 3200 patients (18.9%) with dermatitis has been identified as having a benign tumor and / or malignant cancer diagnosis, 1207 (37.7%) of them also had positive test results for contact allergy .
Approximate analysis of the data showed "a confident and significant association" between contact allergy and the presence in the Register of Cancer (odds ratio 1.1). Odds ratios for different groups of cancer were calculated using logistic regression analysis, after adjusting for age and sex.
Breast cancer (odds ratio 0.80) and non-melanoma skin cancer (odds ratio 0.83) in both sexes, were found to inversely and significantly associated with contact allergy. Bladder cancer is positively and significantly associated with contact allergy (odds ratio 1.44).
The authors also studied the interaction between the different subtypes of cancer and sex, and only found a link to brain cancer / central nervous system. Following a standardized regression in women with dermatitis between brain cancer / central nervous system and contact allergy to reverse the trend of association (odds ratio 0.36).
Further studies, standardized by environmental factors such as smoking and socio-economic background needed to understand the role of contact allergy in the development of cancer, the scientists conclude.