Atopy and contact hypersensitivity: a reassessment of the relationship using objective measures.

BACKGROUND There is a big contradiction in the medical literature regarding the relationship between atopy and contact hypersensitivity. Some researchers believe that atopy would prevent, whereas others believe that it would promote, the development of contact allergy. Possible causes of this confusion range from different study populations to different definitions of atopy. OBJECTIVE To evaluate the relationship between atopy and contact hypersensitivity in a well-defined general population sample using objectively measurable markers. METHODS I studied 135 randomly selected students from 5 vocational schools: 73 women and 62 men aged 18 to 19 years. The following atopy markers were tested: positive skin prick test results, positive Phadiatop test results, and total IgE levels greater than 120 kU/L. Contact hypersensitivity was detected by using patch tests. Statistical analyses included the Fisher exact test, the Mann-Whitney U test, and calculation of odds ratios. RESULTS At least 1 positive skin prick test result was found in 23.7% (95% confidence interval [CI], 16.5%-30.9%) of study participants, positive Phadiatop test results were found in 20.0% (95% CI, 13.3%-26.7%), and total IgE levels greater than 120 kU/L were found in 23.7% (95% CI, 16.5%-30.9%). Positive patch test reactions were found in 28.1% (95% CI, 20.6%-35.7%) of participants, most frequently to thimerosal (18.5%; 95% CI, 12.0%-25.1%) and nickel (9.6%; 95% CI, 4.6%-14.6%). For persons with atopy markers, odds ratios for contact hypersensitivity ranged from 1.0 to 3.2, the highest being for nickel hypersensitivity among those with total IgE levels greater than 120 kU/L. None of these relationships were statistically significant. CONCLUSION Atopy and contact hypersensitivity are independent phenomena.