SummaryBackgroundMethylisothiazolinone (MI) is used as a preservative in occupational and household products, and cosmetics. It is a part of the preparation of methylchloroisothiazolinone (MCI)/MI, which is patch tested in water in the European baseline series. However, this preparation fails to detect a significant percentage of allergic contact reactions to MI.ObjectivesTo investigate whether a separate test preparation with MI should be included in the European baseline series.MethodsLiterature survey.ResultsIn consecutively tested dermatitis patients, the contact allergy rate for MI varies between 0.6% and 6%, with a marked increase in recent years. The contact allergy rate for MI alone, not detected with MCI/MI, varies between 0% and 1.6%. Most cases are relevant, as shown by repeated open application test studies, and are mainly related to exposure from cosmetic products.ConclusionsOwing to the increase in contact allergy to MI not detected with MCI/MI, it is recommended that MI in water at 2000 ppm be included in the European baseline series. With the Finn Chamber® (diameter, 8 mm) technique, a volume of 15 µl should be applied, giving a dose of 60 µg/cm2.

Our results demonstrate that the low concentrations of formaldehyde often found in skincare products by the CA method are sufficient to worsen an existing dermatitis in formaldehyde-allergic individuals.

contact allergy to the TDM is common and inclusion into the Swedish baseline series should be considered.