Tetrahydrofurfuryl Methacrylate and Isobornyl Acrylate: Possible New Sensitisers in Hearing Aid Ear Moulds

BACKGROUND: Allergic contact dermatitis from hearing aid ear moulds is infrequently reported. OBJECTIVES: To identify cases of allergic contact dermatitis from hearing aid moulds in a cohort of patients investigated between 2022 and 2025 at Amsterdam University Medical Center. MATERIALS AND METHODS: Retrospective analysis of patients referred for investigation of suspected allergic reactions to ear moulds. RESULTS: Of 20 patients with suspected allergic reactions to ear moulds, 8 (40%) had positive patch tests to (meth)acrylates considered to be probably relevant. All eight reacted to tetrahydrofurfuryl methacrylate, of whom five had a positive reaction to this hapten only. The other three all co-reacted to isobornyl acrylate and 1,6-hexanediol diacrylate. None had positive patch tests to hydroxyethyl methacrylate. CONCLUSIONS: There are strong indications that tetrahydrofurfuryl methacrylate and isobornyl acrylate are relevant contact allergens present in hearing aid ear moulds. Hydroxyethyl methacrylate did not identify a single case of contact allergy to these materials.