BACKGROUND: Contact allergy is a major public health problem in industrialized countries. Hitherto, known risk factors for contact allergy have mainly included increased exposure to allergens. There are no published data on the relation between smoking and contact allergy.

OBJECTIVE: To investigate the association between smoking and contact allergy.

METHODS: The study population comprised a cross-sectional, general population-based sample of 15- to 69-year-old persons living in Copenhagen, Denmark. A total of 1056 persons (73.6% of the invited) were given a patch test (TRUE test). Contact allergy was defined as a positive patch test result to at least 1 of 23 allergens. Nickel contact allergy was defined as a positive patch test reaction to nickel. Allergic nickel contact dermatitis was defined as a history of eczema on exposure to metallic objects and a positive patch test reaction to nickel. A detailed smoking history was obtained in a questionnaire.

RESULTS: Contact allergy (adjusted odds ratio, 1.8; 95% CI, 1.2 to 2.9), nickel contact allergy (adjusted odds ratio, 2.7; 95% CI, 1.4 to 5.2), and allergic nickel contact dermatitis (adjusted odds ratio, 3.0; 95% CI, 1.5 to 6.2) were significantly associated with a smoking history of more than 15 pack-years. Moreover, these associations showed a significant dose-response relation, and they were independent of sex, age, and exposure to nickel, as reflected by a history of ear piercing.

CONCLUSIONS: These data raise the hypothesis that smoking increases the risk of contact allergy. Further epidemiologic studies and investigations into the possible mechanisms are warranted.