Methylisothiazolinone is an antimicrobial and preservative in the form of a soluble concentrated liquid or solid that is used in a variety of applications, such as personal care and cleaning products.
Methylisothiazolinone is a highly corrosive chemical that has been found to be toxic when ingested, inhaled, or applied to the skin or eyes in animal studies according to the EPA in the 1998 document, "Reregistration Eligibility Decision, Methylisothiazolinone."
Methylisothiazolinone commonly goes by MIT, but according to the Environmental Protection Agency (EPA), the Cosmetic Ingredient Review, PubChem, and ChemSpider, it can go by some of the following names as well:
Synonyms: MI; 2-Methyl-3(2H)-isothiazolone, 3(2H)-Isothiazolone, 2-methyl-, Caswell No. 572A, 2-Methyl-4-isothiazoline-3-one
Trade Names: KathonCG 243; Kordek 50; Kordek 50C; Kordek MLX; Microcare MT; N-Methylisothiazolin-3-one; N-Methylisothiazolone; Neolone; Neolone 950; NeoloneCapG; Neolone M 10; Neolone M 50; Neolone PE; Optiphen MIT; OriStar MIT; ProClin 150; ProClin 950; SPX; and Zonen MT
CAS Number: 2682-20-4
Molecular Formula: C4H5NOS
Methylisothiazolinone is used as a preservative in several cleaning products, including green cleaning ones, such as laundry detergents, liquid dish detergents, cream cleansers, all-purpose cleaners, window cleaners, floor cleaners, countertop sprays, stain removers, linen washes, room sprays, air fresheners, carpet shampoos, and wipes. Also, it is important to point out that it is often used in conjunction with benzisothiazolinone, a synthetic preservative.
In addition to its use in cleaning products, methylisothiazolinone has a dizzying number of other applications, such as preventing bacteria, fungi, mold, mildew, sapstain, and algae from forming. It is used in paper mills, oil field operations, metalworking fluids, water cooling and treatment systems, and building materials, such as adhesives, paints, resins, emulsions, and wood products. Also, it is used in almost any personal care product you can think of, including, but not limited to, diaper creams, shampoos, conditioners, body washes, moisturizers, sunscreens, shaving cream, feminine hygiene washes, and mascara.
Product Brands Containing Methylisothiazolinone
To see if certain products contain methylisothiazolinone, try searching the U.S. Department of Health and Human Services Household Products Database, the Environmental Working Group's (EWG) Guide to Healthy Cleaning, the Good Guide, or the EWG's Skin Deep Cosmetic Database.
When methylisothiazolinone is used in personal care preparations or in the manufacture of paper products that may come into contact with food it is monitored by the U.S. Food and Drug Administration (FDA). For other uses, such as pesticides and cleaning products, it is monitored by the EPA.
Health and Safety
Due to findings in the 1998 EPA study, the EPA established guidelines for those who work with this chemical, such as mixers and loaders, to wear protective clothing, gloves, eyewear, respirators, etc. On the other hand, no special measures were noted for homeowners who use products that contain methylisothiazolinone, such as paint and adhesives, because the EPA deemed the risks were "acceptable" due to the products being heavily diluted.
Since the EPA's reregistration of the chemical, it appears Methylisothiazolinone has been suspected of being a neurotoxin. A 2002 and 2006 scientific study published in The Journal of Pharmacology and Experimental Therapeutics and The Journal of Neuroscience respectively, showed in vitro neurotoxicity and that chronic exposure had toxic effects on neuron cultures.
With regard to its use in cosmetics, restrictions have been put in place in countries, such as Canada and Japan, as noted in the EWG's Skin Deep Cosmetic Database. In the United States, the Cosmetic Ingredient Review (CIR) panel stated in a 2010 study that methylisothiazolinone is safe and wouldn't cause sensitization when used in cosmetics at a certain concentration—up to 100 ppm or 0.01 percent. However, in a 2013 study published in Dermatitis, methylisothiazolinone was called the "Allergen of the Year for 2013," so it seems it may not be so safe after all.
This chemical is toxic to freshwater, estuarine, and marine organisms according to the EPA. However, it is not expected to bioaccumulate or persist in the environment.
There are plenty of preservatives and antimicrobial chemicals on the market that don't have any known issues, so seek out green products that don't contain methylisothiazolinone if you're concerned. Carefully read ingredient labels and product reviews to help you know what you're getting.