Methylchloroisothiazolinone


Methylchloroisothiazolinone, also referred to as MCI, is a preservative with antibacterial and antifungal effects within the group of isothiazolinones. These compounds have an active sulphur moiety that is able to oxidize thiol-containing residues, thereby effectively killing most aerobic and anaerobic bacteria. Methylchloroisothiazolinone 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, and bronopol.

Safety

Methylchloroisothiazolinone can cause allergic reactions in some people. The first publication of the preservative as a contact allergen was in 1988. Cases of photoaggravated allergic contact dermatitis, i.e. worsening of skin lesions after sun exposure, have also been reported.
In pure form or in high concentrations, methylchloroisothiazolinone is a skin and membrane irritant and causes chemical burns. In the United States, accepted concentrations are 15 ppm in rinse-offs and 8 ppm in other cosmetics. In Canada, methylchloroisothiazolinone may only be used in rinse-off products in combination with methylisothiazolinone, the total concentration of the combination may not exceed 15 ppm.
As of 2008, the International Agency for Research on Cancer, did not list methylchloroisothiazolinone as a known, probable, or possible human carcinogen, nor have in vivo tests found evidence of carcinogenic activity.