Allergic or Not: Final Interpretation of Doubtful Patch Test Reactions From the North American Contact Dermatitis Group, 2019-2020.

Background: Doubtful patch test reactions generally do not meet criterion for positivity in patch testing. However, the North American Contact Dermatitis Group (NACDG) allows for doubtful reactions to be coded with a final determination of "allergic/positive" based on the temporal pattern, appearance, known characteristics of the allergen, and/or other supportive patch test reactions. Objectives: To analyze NACDG data from the 2019-2020 patch test cycle to identify patterns in the interpretation and relevance of doubtful reactions. Methods: The frequency and proportions of doubtful reactions were tabulated and analyzed for patterns. Statistical analyses were limited to allergens with ≥30 doubtful reactions to ensure adequate sample size. Results: Of patch-tested patients, 31.9% (1315/4121) had ≥1 doubtful reaction. Of 2538 total doubtful reactions, 46% (n = 1167) had a final interpretation of "allergic/positive." The allergens with the highest proportion of doubtful reactions at the final visit were hydroperoxides of linalool 1% (4.5%), fragrance mix I 8.0% (3.9%), and cetrimonium chloride 0.5% (3.4%). Methylchloroisothiazolinone/methylisothiazolinone (MCI/MI) 0.02% (P < 0.001), MI 0.2% (P < 0.001), nickel sulfate hexahydrate 2.5% (P = 0.001), and neomycin sulfate 20.0% (P = 0.003) doubtful reactions were more likely to be interpreted as allergic than nonallergic. Methyldibromoglutaronitrile/phenoxyethanol 0.2% (P < 0.001), oleamidopropyl dimethylamine 0.1% (P < 0.001), formaldehyde 2.0% (P < 0.001), cetrimonium chloride 0.5% (P < 0.001), benzophenone-4 (sulisobenzone) 10% (P < 0.001), iodopropynyl butylcarbamate 0.5% (P < 0.001), cocamidopropyl betaine 1.0% (P = 0.002), and benzisothiazolinone 0.1% (P = 0.012) doubtful reactions were less likely to be interpreted as allergic. Of the 1167 doubtful reactions interpreted as allergic, 84.9% had current relevance. Conclusions: Doubtful reactions were common and approximately one half were coded with a final interpretation of "allergic/positive." Of those, most were clinically relevant. MCI/MI, MI, nickel, and neomycin were more likely to be interpreted as allergic.

Patch Testing to Mentha piperita (Peppermint) Oil: The North American Contact Dermatitis Group Experience (2009-2020).

Background: Mentha piperita (MP; peppermint) oil has many commercial uses. Objective: To characterize the epidemiology of contact allergy to MP oil 2% petrolatum. Methods: Retrospective analysis of North American Contact Dermatitis Group data (2009-2020). Results: Of 28,128 patients tested to MP, 161 (0.6%) had an allergic reaction. Most allergic patients were female (77.0%) and/or over 40 years of age (71.4%). The most common anatomical sites of dermatitis included face (31.7%; of these, one-third specified lips), hands (17.4%), and scattered/generalized (18.6%). Nearly one-third (30.4%) of reactions were strong (++)/extreme (+++), and 80.1% were considered currently relevant. Common sources included oral hygiene preparations, foods, and lip products. Co-reaction with at least 1 of the other 19 fragrance/plant-related screening test preparations occurred in 82.6% (133/161) of MP-allergic patients, most commonly Cananga odorata oil (42.9%), fragrance mix I (41.0%), hydroperoxides of linalool (35.7%), Compositae mix (35.4%), Jasminum officinale oil (31.9%), Myroxylon pereirae (31.7%), and propolis (28.1%). Co-reaction with at least 1 of the 3 most commonly used fragrance screening allergens (fragrance mix I, fragrance mix II, and/or Myroxylon pereirae) was 59.6%. Conclusions: Twelve-year prevalence of MP allergy was 0.6%. Approximately 40% of cases would have been missed if only fragrance screening allergens were tested.

Occupational Contact Dermatitis in Construction Workers: A Retrospective Analysis of the North American Contact Dermatitis Group Data, 2001-2020.

Background: Construction workers (CWs) are at risk for occupational contact dermatitis (CD) owing to workplace exposures. Objective: Determine the prevalence of occupational allergic CD and characterize common occupational allergens in CWs referred for patch testing in the United States and Canada. Methods: Retrospective cross-sectional analysis of patients patch tested by the North American Contact Dermatitis Group from 2001 to 2020. Results: Of 47,843 patch-tested patients, 681 (1.4%) were CWs. Compared with non-CWs, CWs were more likely to be male (91.0% vs 30.9%) have occupational skin disease (36.9% vs 11.4%) and have hand involvement (37.2% vs 22.5%) (all P < 0.0001). Of 681 CWs, 60.1% (411) had clinically relevant positive patch test reactions, and nearly 1/3 of CWs (128) had occupationally relevant reactions. Most common occupationally relevant allergens were potassium dichromate 0.25% pet. (30.5%, 39/128), bisphenol A epoxy resin 1% pet. (28.1%, 36/128), carba mix 3% pet. (14.8%, 19/128), cobalt (ii) chloride hexahydrate 1% pet. (14.1%, 18/128), and thiuram mix 1% pet. (14.1%, 18/128). Top sources of occupationally relevant allergens were cement/concrete/mortar (20.4%, 46/225), gloves (15.1%, 34/225), and coatings (paint/lacquer/shellac/varnish/stains) (9.8%, 22/225). Conclusions: Occupational CD in North American CWs is common. In this group, frequently identified etiological sources of occupational allergic CD included metals, epoxy resin, and rubber.