Background Isoeugenol is an important fragrance allergen. The cosmetic industry was recommended voluntarily to reduce concentrations of isoeugenol in finished cosmetic products from 0·2% to 0·02% in 1998. It was suspected that this would reduce the incidence of patch test positivity in individuals undergoing routine patch testing after approximately 2–3 years (the Dillarstone effect).
Objectives To review our patch test data since the change in practice by industry, to see if there has been an observable decrease in isoeugenol contact sensitivity.
Methods We retrospectively analysed all subjects patch tested to isoeugenol 1% pet. in the St John’s Department of Cutaneous Allergy over a period of 5 years, commencing 3 years after the changes.
Results We identified 3636 subjects, 97 of whom were positive for isoeugenol. Year-on-year incidence shows an increasing trend, with an overall incidence of 2·67%. Using the exact Cochran–Armitage test, this ascending trend is statistically significant (P = 0·0182). Seventy-two of 97 isoeugenol-positive subjects were also positive to fragrance mix I. Other fragrances positive in these 97 patients included Myroxylon pereirae (30%), Evernia prunastri (22%) and eugenol (15%).
Conclusions We suspect that the increasing trend may be due to allergen substitution with compounds chemically related to isoeugenol, or which hydrolyse to isoeugenol itself.