Quantitative aspects of isoeugenol contact allergy assessed by use and patch tests

The clinical implications of sensitization to the fragrance material isoeugenol were studied in 19 subjects. Patch testing with serial dilutions of isoeugenol and a repeated open application test (ROAT) were performed. The minimum effect level under patch test conditions was below 0.01% isoeugenol in 4/19 (20%) of the test subjects. The ROAT was performed with a test solution of 0.2% isoeugenol in ethanol, which is the recommended maximum concentration used in perfumes, ethanol being applied as vehicle control. 4 weeks was the maximum exposure period. The upper arm was used as test site the 1st 14 days and the upper arm as well as the neck for the next 14 days. 12/19 (63%) of test subjects had a positive ROAT. 4 of the responders (33%) reacted beyond day 7, but none after day 14. Use testing on the neck 14 days did not add any further ROAT-positive cases, compared with testing on the upper arm. The sensitivity found on patch testing may be a guidance for the outcome of use tests with the same compound. In this study, all subjects with a positive use test to isoeugenol 0.2% in ethanol also demonstrated on patch testing a minimum effect level of 0.2% or lower. Data from serial dilution patch and use tests may contribute significant information to assessment of the relationship between patch test responses and clinical contact hypersensitivity, and thus the safety of allergens used in cosmetics.