Methylchloroisothiazolinone (5-chloro-2-methyl-4-isothiazolin-3-one) is a preservative with antibacterial and antifungal effects within the group of isothiazolinones. It is effective against gram-positive and gram-negative bacteria, yeast, and fungi.
Methylchloroisothiazolinone is found in many water-based personal care products and cosmetics. Methylchloroisothiazolinone was first used in cosmetics in the 1970s. It is also used in glue production, detergents, paints, fuels, and other industrial processes. Methylchloroisothiazolinone is known by the registered tradename Kathon CG when used in combination with methylisothiazolinone.
Methylchloroisothiazolinone may be used in combination with other preservatives including ethylparaben, benzalkonium chloride, or 2-bromo-2-nitropropane-1,3-diol.
In pure form or in high concentrations, methylchloroisothiazolinone can be a skin and membrane irritant or cause chemical burns. It was largely removed from most cosmetic products except for those with only short duration skin contact such as rinse-offs. Its inclusion in certain forms makes it more acceptable to sensitive users, so it can be found in cosmetic creams and lotions which require skin contact. In the United States, accepted concentrations are 15 ppm in rinse-offs and 8 ppm in other cosmetics.
The International Agency for Research on Cancer (IARC), does not currently list methylchloroisothiazolinone as a known, probable, or possible human carcinogen, nor have in vivo tests found evidence of carcinogenic activity. Methylchloroisothiazolinone is an allergen for 1.7% of individuals. A common indication of an allergic reaction is eczema-like symptoms on the hands and wrists. These symptoms will disappear several weeks after exposure is ceased. Common points of exposure in household items are shampoos, soaps and pre-moistened bath wipes.
- Record in the Household Products Database of NLM
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