: Contact allergy to the cosmetics preservative methylisothiazolinone plus methylchloroisothiazolinone (MI/MCI, Kathon CG, Euxyl K 100) is reviewed. MI/MCI has a strong sensitizing capacity as shown by predictive tests. Its use in cosmetic products of the stay-on variety at levels of 7 ppm or more has caused many cases of sensitization; such application of the preservative should be discouraged. Use of MI/MCI in rinse-off products at low levels does not carry a significant risk of induction and/or elicitation of hypersensitivity reactions in consumers. Most cases of contact allergy can be demonstrated by patch testing with MI/MCI 100 ppm in water, which should be added to any standard series.
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