LAUSR

Background: Differences in consumer product availability, distribution, and use may lead to national differences in contact sensitization frequencies. Objective The aim of the study was to describe the differences in contact allergy between the United States (US) and Canada. Methods This is a retrospective cross-sectional analysis of the North American Contact Dermatitis Group data from 2005 to 2016. Frequencies of demographics, clinical characteristics, positive reactions, trends, and occupations were calculated. Results A total of 28,640 patients underwent patch testing. At least 1 positive patch test was observed in 18,599 patients (US, 11,641 [66.5%]; Canada, 6958 [62.5%]). When comparing the 2 groups, US positive reactions were more likely to occur in male patients (odds ratio [OR] = 1.40, 95% confidence interval [CI] = 1.31–1.49), older than 40 years (OR = 1.30, 95% CI = 1.22–1.38), Black (OR = 2.67, 95% CI = 2.24–3.19) or Hispanic race (OR = 3.53, 95% CI = 2.61–4.78), and/or patients with scattered generalized dermatitis (OR = 1.96, 95% CI = 1.80–2.13). They were less likely to occur in patients with eczema (OR = 0.61, 95% CI = 0.57–0.65) and Asian race (OR = 0.50, 95% CI = 0.44–0.56). Nickel (US, 16.0%; Canada, 22.4%) and methylisothiazolinone (US, 13.4%; Canada, 11.0%) were the top allergens. The third most frequent was neomycin (US, 11.7%) and fragrance mix I (Canada, 10.2%). Conclusions National differences in allergen prevalence and trends exist in North America.