Background: 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.
Objectives: 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.
Results: 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).
Conclusions: 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.
From the *Department of Occupational and Environmental Dermatology, Skåne University Hospital, Lund University, Malmö, Sweden; †Allergy Center and Department of Dermatology, University Hospital, Republic University of Uruguay, Montevideo; ‡Department of Dermatology and Allergy Centre, Odense University Hospital, University of Southern Denmark; §Department of Dermatology, University Hospital Jena, Germany; ∥Department of Dermatology, National Skin Center, Singapore, Singapore; ¶Contact Allergy Unit, Department of Dermatology, University Hospital K.U. Leuven, Belgium; #MGM Medical College, Mumbai, India; and **Department of Dermatology, Fujita Health University School of Medicine, Toyoake, Japan.
The authors are on behalf of the International Contact Dermatitis Research Group.
Address reprint requests to Malin Engfeldt, MSc (Chem Eng), Department of Occupational and Environmental Dermatology, Skåne University Hospital, SE-205 02 Malmö, Sweden. E-mail: email@example.com.
The authors have no funding or conflicts of interest to declare.
All authors have participated sufficiently to take public responsibility for the work.