Patch testing with hydroxyisohexyl 3‐cyclohexene carboxaldehyde ( HICC ) – a multicentre study of the S wedish C ontact D ermatitis R esearch G roup

Summary Background In 2014, the fragrance hydroxyisohexyl 3‐cyclohexene carboxaldehyde (HICC) was excluded from the Swedish baseline series. Objectives To study (i) whether fragrance mix ( FM ) II with 5% HICC detects more positive reactions than usual FM II with 2.5% HICC , and (ii) the reproducibility of patch testing with HICC . Methods Two thousand one hundred and eighteen dermatitis patients at five S wedish dermatology departments were consecutively tested with FM II 14% pet., FM II 16.5% pet., and duplicate preparations of HICC 5% pet. Results Of the patients, 3.2% reacted to FM II 14%, and 1.5% reacted to HICC . Separate testing with HICC detected 0.3% reactions without concomitant reactivity to FM II . FM II with 5% HICC did not give rise to more irritant reactions or signs of active sensitization than FM II with 2.5% HICC . Patch testing with duplicate applications of HICC increased the overall prevalence of HICC contact allergy to 1.9%. Conclusion FM II with 5% HICC does not detect more positive reactions than FM II with 2.5% HICC . Separate testing with HICC does not detect a sufficient proportion of patients who react only to HICC , without concomitant reactions to FM II , to warrant its inclusion in a baseline series.