North American Contact Dermatitis Group Patch Test Results: 2021–2022

<u><b><i></i></b></u> <u><b><i>Background:</i></b></u> Patch testing is an important diagnostic tool for the assessment of allergic contact dermatitis (ACD). <u><b><i>Objective:</i></b></u> This study documents the North American Contact Dermatitis Group (NACDG) patch testing results from 2021 to 2022. <u><b><i>Methods:</i></b></u> At 12 centers in North America, patients were tested in a standardized manner with a screening series of 80 allergens. <u><b><i>Results:</i></b></u> Overall, 3056 patients were tested; 2200 (72.0%) had at least 1 positive/allergic patch test reaction and 1412 patients (46.6%) had a primary diagnosis of ACD. The most commonly positive allergens were nickel sulfate hexahydrate 5% and 2.5% petrolatum (24.9% and 22.1%, respectively), methylisothiazolinone (MI) (11.5%), hydroperoxides of linalool (10.1%), cobalt chloride hexahydrate (9.2%), and methylchloroisothiazolinone/methylisothiazolinone (9.0%). Compared with 2019-2020, prevalence of the top 20 allergens statistically increased for nickel (<i>P</i> < 0.001), cobalt (<i>P</i> < 0.01), gold (<i>P</i> < 0.001), hydroperoxides of limonene (<i>P</i> < 0.001), oleamidopropyl dimethylamine (<i>P</i> < 0.01), dimethylaminopropylamine (<i>P</i> < 0.01), and ammonium persulfate (<i>P</i> < 0.001). MI positivity continued to decrease from its peak in 2017-2018. More than one-fifth of patients (n = 640, 21.1%) had at least one clinically relevant reaction to an allergen/substance not present in the NACDG screening series. <u><b><i>Conclusions:</i></b></u> The epidemic of MI contact allergy in North America appears to continue its descent. Fragrance allergy is still very common, but the composition of fragrance allergy markers appears to be changing. Patch testing using a robust screening series, and supplemental allergens as indicated, is necessary for the comprehensive evaluation of ACD.