The effect of race and ethnicity on patch test results

Allergic contact dermatitis is a condition that may be affected by differences in genetic and environmental factors. Race and ethnicity are possible examples of the former.

The objective of this study was to examine the differences in patch test results between white and black individuals tested by the members of the North American Contact Dermatitis Group from July 1, 1992, to June 30, 1998.

Patients evaluated in our patch test clinics were exposed to a standardized patch testing technique involving a standard series of 41 allergens in total. The standard series we used varied over the 6 years of the study in 2-year cycles. The series was the same at all centers during each of these 2-year cycles: 1992-94, 1994-96, and 1996-98. Over a 6-year period, our group tested 9624 patients. Of those individuals, 8610 (89.5%) were white and 1014 (10.5%) were black.

Allergic contact dermatitis and irritant contact dermatitis were the final diagnoses assigned by the investigators to individuals of the 2 races: 49% and 16%, respectively, for the white patients and 46% and 15%, respectively, for the black patients. In at least one of the three 2-year periods, testing in white patients revealed higher rates of sensitization to formaldehyde, glutaraldehyde, and a number of the formaldehyde-releasing preservatives, as well as lanolin, epoxy resin, thioureas, and balsam of Peru. Black patients exhibited higher rates of sensitization to para-phenylenediamine, cobalt chloride, thioureas, and p-tert-butylphenol formaldehyde resin in at least one of the 2-year periods.

In this test population, we found no differences in the overall response rate to allergens. There were some differences between white and black patients in their response to specific allergens. These differences, although possibly related to genetic factors based on race, are more likely related to differences in allergen exposure determined by ethnicity.