Multicenter Patch Testing With Methylchloroisothizoline/Methylisothiazolinone in 100 and 200 ppm Within the International Contact Dermatitis Research Group

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The preservative methylchloroisothiazolinone/methylisothiazolinone (MCI/MI) is a well-known contact sensitizer. Historically, there have been different opinions on the optimal patch test concentration of MCI/MI, and both 0.01% and 0.02% aqueous (aq.) have been proposed. In 2011, based on literature reviews, it was recommended that the concentration of 0.02% aq. should be used in the international baseline series.


The aim of this study was to verify the recommendation from 2011 by comparing the patch test results from consecutive patch testing with MCI/MI 0.01% and 0.02% in clinics representing countries around the world.

Patients and Methods

Two thousand seven hundred three consecutive patients with dermatitis in 8 dermatology clinics representing 8 countries were patch tested with MCI/MI 0.01% aq. and, in parallel with MCI/MI 0.02% aq., provisionally included in the baseline series.


Contact allergy to MCI/MI at 0.01% and 0.02% was found in 3.7% and 5.6% of the patients, respectively (P < 0.001).


Methylchloroisothiazolinone/MI 0.02% aq. (dose, 6 μg/cm2) diagnoses significantly more contact allergy than 0.01% (dose, 3 μg/cm2), without resulting in more adverse reactions. Methylchloroisothiazolinone/MI at 0.02% aq. should therefore be continuously used in the international baseline series.

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