Methylchloro-isothiazolinone revisited.

Preservatives are a class of allergens that is well represented in testing series. There are 5 preservatives in the TRUE test, 4 preservatives in the European series, and 13 in the North American Series. Methylchloroisothiazolinone/methylisothiozolinone (MCI/MI) (Kathon CG, Rohm and Haas, Spring House, PA) is a relatively new allergen that was introduced in 1980 in the United States. Its use rapidly increased until reports of contact allergy became an issue. Allowable levels of MCI/MI in products, sensitivity rates, and use rates vary by country. The overall incidence of sensitivity for this allergen, as reported by the North American Contact Dermatitis Group, is similar to other allergens in the preservative class.