An epidemiological study of contact allergy to 5-chloro-3-methyl isothiazolone/3-methyl isothiazolone in Strasbourg.

In Strasbourg, the incidence of allergy to the mixture of 5-chloro-3-methyl isothiazolone and 3-methyl isothiazolone (MCI) in 540 patients (313 women and 227 men), routinely tested with this preservative as part of the standard series of allergens, was 1.11%. The frequency was 1.6% in women and 0.44% in men. A total of 6 cases of allergy, 5 in women and 1 in a man, to MCI were detected. In 5 cases out of 6, the patient was shown to have used cosmetic products containing this preservative. Finally, in 5 cases out of 6, the subjects allergic to MCI also tested positively for nickel, while only 15% of the total of 540 subjects tested with MCI had a nickel allergy confirmed by patch tests.