Methylisothiazolinone (MIT) and Methylchloroisothiazolinone (CMIT) are widely used preservatives found in liquid cosmetic and personal care products.[3][4] Both chemicals inhibit bacterial growth in cosmetic products on their own, but they are most commonly used as a mixture in products.[5]
Organ System Toxicity: Rats exposed to highly concentrated MIT (over 50%) showed a range of symptoms, including significant body weight gain and death. Autopsies revealed that death was due to reddened lungs and swollen intestines.[6] This may be a concern to factory workers who are exposed to high concentrations of MIT. Currently, there are no National Institute for Occupational Safety and Health (NIOSH) guidelines to limit MIT/CMIT exposure in the workplace.[7][8]
Allergies: Methylisothiazolinone (MIT) and Methylchloroisothiazolinone (CMIT) are two of the most predominant contact allergens found in cosmetic products.[9] In a clinical study, researchers found that dermal irritation most commonly occurs in products with CMIT and MIT/CMIT mixtures, but is not as common in products with only MIT.[10][11] The American Contact Dermatitis Society named MIT Allergen of the Year for 2013 due to the skin sensitization resulting from dermal exposure to it.[12][13]
Debate exists about the concentrations of MIT/CMIT that trigger an allergic reaction, and harmful effects have been found ranging from 7.5 to 100 parts-per-million.
Neurotoxicity: In vitro cell studies on Methylisothiazolinone (MIT) showed signs of neurotoxicity when cerebral cortex cells were exposed to liquid MIT.[14] However, animal studies did not find significant signs of neurotoxicity when rodents were exposed to MIT through drinking water.[15]
Europe, along with the European Society of Contact Dermatitis (ESCD), recommends that MIT be discontinued from use in leave-on skin products.[16]
If you are allergic, read labels and avoid products with Methylisothiazolinone (MIT) or Methylchloroisothiazolinone (CMIT). Especially avoid products with a mixture of CMIT and MIT. If you are not allergic, MIT and CMIT are among the safer preservatives with regard to long-term chronic health effects.
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[1] Rohm & Haas (2002). Acute Inhalation toxicity study in rate (methylisothiazolinone 53.52% active ingredient). Rohm & Haas Chemicals, LLC Report, 06R-1002.
[2] Burnett, C. L., Bergfeld, W. F., Belsito, D. V., Klaassen, C. D., Marks, J. G., Shank, R. C., … & Andersen, F. A. (2010). Final report of the safety assessment of methylisothiazolinone. International journal of toxicology, 29(4 suppl), 187S-213S.
[3] Methylchloroisothiazolinone. Available Online: http://www.ewg.org/skindeep/ingredient/703924/METHYLCHLOROISOTHIAZOLINONE/. Accessed April 26, 2022.
[4] Methylisothiazolinone and Methylchloroisothiazolinone Available Online: http://www.cosmeticsinfo.org/ingredient/methylisothiazolinone-and-methylchloroisothiazolinone. Accessed April 26, 2022.
[5] Burnett, C. L., Bergfeld, W. F., Belsito, D. V., Klaassen, C. D., Marks, J. G., Shank, R. C., … & Andersen, F. A. (2010). Final report of the safety assessment of methylisothiazolinone. International journal of toxicology, 29(4 suppl), 187S-213S.
[6] Rohm & Haas (2002). Acute Inhalation toxicity study in rate (methylisothiazolinone 53.52% active ingredient). Rohm & Haas Chemicals, LLC Report, 06R-1002.
[7] EWG. Methylchloroisothiazolinone. https://www.ewg.org/skindeep/ingredients/703924-methylchloroisothiazolinone/. Accessed April 26, 2022.
[8] NIOSH Methylisothiazolinone Guidelines Accessed Online: https://www.cir-safety.org/sites/default/files/MI_MCI.pdf. Accessed April 26, 2022.
[9] Lundov, M. D., Krongaard, T., Menné, T. L., & Johansen, J. D. (2011). Methylisothiazolinone contact allergy: a review. British Journal of Dermatology, 165(6), 1178-1182.
[10] Burnett, C. L., Bergfeld, W. F., Belsito, D. V., Klaassen, C. D., Marks, J. G., Shank, R. C., … & Andersen, F. A. (2010). Final report of the safety assessment of methylisothiazolinone. International journal of toxicology, 29(4 suppl), 187S-213S.
[11] Lundov, M. D., Krongaard, T., Menné, T. L., & Johansen, J. D. (2011). Methylisothiazolinone contact allergy: a review. British Journal of Dermatology, 165(6), 1178-1182.
[12] Castanedo-Tardana, M.P., & Zug, K.A. (2013). Methylisothiazolinone. Dermatitis, 24(1), 2-6.
[13] Cosmetic Ingredient Review Expert Panel (1992). Final Report on the Safety Assessment of Methylisothiazolinone and Methylchloroisothiazolinone. Journal of the American College of Toxicology, 11(1).
[14] Burnett, C. L., Bergfeld, W. F., Belsito, D. V., Klaassen, C. D., Marks, J. G., Shank, R. C., … & Andersen, F. A. (2010). Final report of the safety assessment of methylisothiazolinone. International journal of toxicology, 29(4 suppl), 187S-213S.
[15] Burnett, C. L., Bergfeld, W. F., Belsito, D. V., Klaassen, C. D., Marks, J. G., Shank, R. C., … & Andersen, F. A. (2010). Final report of the safety assessment of methylisothiazolinone. International journal of toxicology, 29(4 suppl), 187S-213S.
[16] Cosmetics Europe: the personal care association. Recommendation. Brussels, 12 December 2013.
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