Methylisothiazolinone (MIT) is a preservative commonly used in shampoos and other personal-care and household products to prevent bacterial growth. In laboratory studies, MIT has been shown to damage nerve cells when those cells are directly exposed to the chemical. In these experiments, cultured neurons exposed to MIT were injured or died, and prolonged exposure to low concentrations interfered with normal neuronal signaling. The concentrations used in some laboratory studies were similar to levels found in certain consumer products.
MIT is classified as a biocide, meaning it is added to products specifically to inhibit microbial growth. There is ongoing debate about whether these laboratory findings translate into meaningful risk for people using products that contain MIT. Critics of the neurotoxicity concern point out that many of the studies involved direct exposure of nerve cells in a laboratory setting, not typical consumer use, and that for systemic neurological effects to occur, MIT would likely need to enter the bloodstream in significant amounts. Others note that long-term, low-level exposure in humans has not been adequately studied, particularly with respect to neurological outcomes.
While definitive conclusions about neurological risk in humans cannot be drawn from existing data, MIT has raised enough concern that it has been restricted or removed from certain products in some countries, particularly leave-on cosmetics. Information about products containing MIT has been compiled by agencies such as the National Institutes of Health, and consumers who wish to avoid this preservative may choose to review ingredient lists or seek MIT-free alternatives.
The National Institute of Health has a list of products containing MIT, just follow this link: MIT.
