Allergic reactivity for different dilutions of eugenol in repeated open application test and patch testing

Background: Eugenol is a known contact sensitiser included in fragrance mix I. Objective: To assess the allergic reactivity to eugenol in different concentrations using patch test as well as repeated open application test (ROAT). Methods: Overall 67 subjects from 6 European dermatology clinics participated in the study. The ROAT was performed for 21 days twice a day, applying 3 dilutions of eugenol (2.7%–0.5%) and a control. Before and after the ROAT, patch testing with 17 dilutions of eugenol (2.0%–0.00006%) and controls was performed. Results: Out of the 34 subjects with contact allergy to eugenol, 21 (61.8%) showed a positive patch test before ROAT was performed, the lowest positive concentration was 0.031%. The ROAT was positive in 19 (55.9%) of the 34 subjects, the time until a positive reaction occurred was negatively associated with the concentration of the ROAT solution, as well as with the allergic reactivity of the subjects as defined by patch testing. In the patch test after ROAT, 20 of the 34 test subjects (58.8%) showed a positive reaction. In 13 (38.2%) of the 34 test subjects, the patch test result was not reproduceable, still 4 (31.0%) of these 13 subjects developed a positive ROAT. Conclusion: Eugenol can provoke a positive patch test reaction in a very low dose; besides, this hypersensitivity may persist even if a former positive patch test is not reproduceable.