Recent safety evaluations of preservative ingredients in personal care and cosmetic products

The Cosmetic Ingredient Review (CIR) is an industry trade association in the United States that evaluates the safety of commonly used ingredients in cosmetics and provides ingredient-specific safety recommendations based on chemistry, consumer use, and toxicology data. One particular ingredient that has received multiple evaluations over the years is the cosmetic preservative mixture of methylchloroisothiazolinone and methylisothiazolinone (MCI/MI). Previously, the CIR concluded that MCI/MI may be safely used in rinse-off products at a concentration up to 15 ppm and in leave-on products at a concentration up to 7.5 ppm. In 2019, the CIR panel decided to re-evaluate their safety assessment of MCI/MI due to multiple reported incidences of skin sensitization (CIR 2019) In a proposed amended report, the CIR noted that some leave-on products with MCI/MI at the recommended safe concentration of 7.5 ppm may still increase the risk of sensitization induction, while an MCI/MI concentration of 15 ppm in rinse-off products was not associated with an increased risk of sensitization.

These findings are in agreement with a previous quantitative risk assessment performed by Cardno ChemRisk (Towle et al. 2018). Specifically, Cardno ChemRisk calculated an estimated daily consumer exposure level for various cosmetic and personal care products using the amount of product applied per application, number of applications per day, a retention factor, the MCI/MI concentration, and body surface area values. This analysis concluded that certain leave-on products (lipstick, body lotion, face cream, liquid foundation, antiperspirant, eye shadow, and perfume) containing 7.5 ppm of MCI/MI may still increase the risk of skin sensitization induction, while rinse-off products (shampoo, body wash, facial cleanser, and conditioner) containing 15 ppm of MCI/MI were not associated with a potential increased risk of skin sensitization induction.