Contact allergy to hydroxyisohexyl 3-cyclohexene carboxaldehyde in Italy: Prevalence, trend, and concordance with fragrance mix 2

Background: Hydroxyisohexyl 3-cyclohexene carboxaldehyde (HICC), contained in fragrance mix 2 (FM2), has been recognized as a contact sensitizer since the mid-1990s. After several attempts to reduce its use during the last two decades, HICC was permanently banned from the European market in August 2021. Objectives: To assess the prevalence and the time trend of contact allergy to HICC and to investigate the concordance of HICC allergy compared to FM2 allergy in an unselected Italian patch test population. Methods/patients: Retrospective analysis on demographics and patch test results of HICC-sensitized and/or FM2-sensitized patients was performed over a 6-year period (2016-2021) at 6 patch test Clinics in Italy. Results: Among 7266 patients (4942 females, 68.0%, mean age 45.4 ± 20.6 years), 1% (70) resulted positive to HICC and 2.1% (153) to FM2. Clinical relevance was documented in 72.9% (51/70) of HICC positive patients. Among the 169 HICC and/or FM2 positive patients, 9.5% had a positive reaction to HICC only, 31.9% to both HICC and FM2, and 58.6% to FM2 only. The prevalence trend line of HICC positive reactions showed a decrease from 1.15% (2016) to 0.96% (2021). Conclusions: We documented a decreasing trend of HICC allergy in Italy, in line with the data recently reported in literature. Nevertheless, HICC should be maintained in the baseline series to monitor the benefits of its ban from the European market.