ABSTRACT Background Limonene and linalool are widely used fragrances in cosmetic and household products. Upon air exposure, they autoxidise into potent sensitisers – hydroperoxides of limonene (Lim‐OOH) and linalool (Lin‐OOH). Objectives The objective of this study is to investigate patch test reactions to Lim‐OOH and Lin‐OOH, and associated characteristics, reaction patterns, including doubtful reactions and co‐reactivity with other fragrance allergens. Method A retrospective analysis was conducted using registry data from 6719 consecutively patch‐tested patients at Gentofte Hospital, Denmark (2014–2025). Doubtful reactions were clinically subclassified as erythematous, only (E) or infiltrated (I). Results The prevalence of positive patch test reactions was 1.6% for Lim‐OOH and 3.1% for Lin‐OOH. Positive Lim‐OOH reactions were less likely in men and in patients with atopic, occupational or hand dermatitis, whilst positive Lin‐OOH reactions were more likely in those > 40 years and less in atopic dermatitis. Most reactions peaked on day 3/4 and were weakly positive. Doubtful I reactions more frequently progressed to positive than doubtful E. Co‐reactivity was observed between Lim‐OOH, Lin‐OOH and other fragrance allergens. Lower test concentrations reduced diagnostic sensitivity. Conclusion Co‐reactivity with other fragrance allergens supports true allergenicity. The currently recommended patch test concentrations (0.3% Lim‐OOH and 1.0% Lin‐OOH) seem optimal and qualify for inclusion in the European baseline series.
Botvid et al. (2026) studied this question.