Long-Term North American Trend in Patch Test Reactions: A 32-Year Statistical Overview (1984-2016).

Allergic contact dermatitis (ACD) remains a public health issue worldwide, despite regulations intended to minimize sensitization. With up-to-date knowledge about which chemicals continue to have high allergenicity, the government/industry can refocus their efforts to be most effective. We reviewed updated data showing common allergens that elicit ACD to determine the progress in reducing sensitization to inform public health policy, government regulation, and industry standards. We compiled data from the North American Contact Dermatitis Group showing patch test results from 1984 to 2016 for 153 compounds. Using these data, we analyzed the trends over time of positive test reactions to determine whether they are increasing or decreasing. Of the 47 compounds with sufficient data to analyze, 23 had a decreasing proportion of positive patch test results over the whole period. An additional 5 had a decreasing proportion over a shorter period. Finally, 4 had an increasing proportion over any period: compositae mix, methylchloroisothiazolinone/methylisothiazolinone, nickel sulfate, and thimerosal mix. The data strongly indicate decreasing and increasing frequency trends and challenge us to seek explanations, which are not yet clear. It is hoped that these data can be valuable in informing public health policy, government, and industry.