Some science behind the scenes
Methylisothiazolinone or MIT or MI, is a powerful biocide and preservative within the group of isothiazolinones, 'used in personal care products'.
Methylisothiazolinone and other isothiazolinone-derived biocides are used for controlling microbial growth in water-containing solutions. Biocidal applications range from industrial water storage tanks to cooling units, in processes as varied as mining, paper manufacturing, metalworking fluids and energy production. In addition, one isothiazolinone, Sea-Nine 211 is used as an antifouling agent. A recent study reported the presence of DCOI in both port water and sediment samples in Osaka, Japan, especially in weakly circulating mooring areas. DCOI levels predicted in marinas are now considered a threat to various marine invertebrate species. Isothiazolinones are also extremely toxic to fish.
The widespread use of isothiazolinones in industrial settings has resulted in a very large number of reported cases of human occupational exposure, leading to chemical burns, contact dermatitis, and allergic sensitization. Inhalation exposure is also very common.
Non-occupational exposure to isothiazolinones by the general population also occurs, albeit at much lower concentrations. These compounds can be detected in air-conditioned indoor air, and are present in a very large number of commonly used cosmetics. “Leave-on” cosmetics (hand-creams, lotions, etc.) contain 15 parts per million (100 micromolar) of combined CMIT/MIT. Kathon has also been used to control slime in the manufacture of paper products that contact food. In addition, this product serves as an antimicrobial agent in latex adhesives and in paper coatings that also contact food.
Some studies have shown MIT to be allergenic and cytotoxic, and this has led to some concern over its use. In 2002, there was an in vitro study of the neurotoxicity of MIT in the department of Neurobiology at the University of Pittsburgh. In that study, it was shown that a short exposure (10 min) to concentrations of MIT of 30-100 micromolar (or 4-12 parts per million) were lethal to mature neurons in tissue culture. The lethal actions of MIT were due to its ability to liberate the metal zinc from intracellular metal-binding sites. The liberated zinc, in turn, triggered a cell death cascade in neurons.
Methylisothiazolinone is commonly used in products in conjunction with methylchloroisothiazolinone, a mixture sold under the registered trade name Kathon CG. A common indication of sensitivity to Kathon CG is allergic contact dermatitis. Sensitization to this family of preservatives was observed as early as the late 1980s. Due to increased use of isothiazolinone-based preservatives in recent years, an increase in reported incidences of contact allergy to this product have been reported, and in 2013 it was dubbed the 2013 Contact Allergen of the Year.
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