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Methylchloroisothiazolinone and Methylisothiazolinone Allergic Contact Dermatitis and the Effect of Patch Test Concentration

Higgins, Eleanor MB, BCH, BAO, MSc, MRCPI; Kirby, Brian MB, FRCPI; Rogers, Sarah MD, MSc, FRCPI, FRCP; Collins, Paul MD, FRCPI

doi: 10.1097/DER.0b013e3182811432

Background The isothiazolinones methylchloroisothiazolinone and methylisothiazolinone (MCI/MI) are the active ingredients in a frequently used preservative in cosmetic, household, and industrial products.

Objectives This study reviewed our department’s cases of allergic contact dermatitis caused by MCI/MI, outlining their clinical presentation and possible sources of sensitization. The effect of changing the concentration of MCI/MI from 0.01% to 0.02% in the British Society for Cutaneous Allergy baseline series was also measured.

Methods A total of 964 patients were patch tested to the British Society for Cutaneous Allergy baseline series in our department over 4 years. Patients were tested either to 0.01% MCI/MI (697) or 0.02% MCI/MI (267).

Results Twenty-one patients (2.2%) had positive reactions to MCI/MI. Of patients tested to 0.02% MCI/MI, 3.8% had a positive reaction compared with 1.6% of those tested to MCI/MI 0.01%. Ten patients (48%) had perianal dermatitis; of these, 50% had used moist toilet wipes.

Conclusions We highlight MCI/MI as important contact allergens found in moist toilet wipes and should be considered particularly in patients with facial, hand, and perianal allergic contact dermatitis. Patch testing to 0.01% MCI/MI may underestimate its allergenic potential, missing more than half of allergic cases compared with testing to 0.02%. To identify isothiazolinone allergy, we recommend that 0.02% MCI/MI should be used in baseline series.

From the Department of Dermatology, St. Vincent’s University Hospital, Dublin, Ireland.

Address reprint requests to Eleanor Higgins, MB, BCH, BAO, MSc, MRCPI, Department of Dermatology, St. Vincent’s University Hospital, Elm Park, Dublin 4, Ireland. E-mail:

The authors have no funding or conflicts of interest to declare.

© 2013 American Contact Dermatitis Society
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