Methylisothiazolinone is a chemical found in shampoo. Recent studies found that the chemical by itself has killed cells in rats’ brains.
The chemical, methylisothiazolinone (MIT), belongs to a class of compounds called biocides. These are used in the manufacture of many common household products and industrial water cooling systems to prevent bacteria from developing.
According to the National Institutes of Health, brands containing MIT include the shampoos Head and Shoulders, Suave, and Clairol, as well as Pantene hair conditioner and Revlon hair color.