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Methylchloroisothiazolinone (MCI) is a preservative used in beauty care products, paint, and cleaning products. It is also known as 3(2H)-Isothiazolone, 5-chloro-2-methyl-; 4-Isothiazolin-3-one, 5-chloro-2-methyl-; 5-Chloro-2-methyl-2H-isothiazol-3-one; and 5-Chloro-2-methyl-4-isothiazolin-3-one.[1] Its CAS Registry Number is 026172-55-4. Methylchloroisothiazolinone is one of two ingredients in the biocide Kathon CG (the other ingredient is methylisothiazolinone).[2] In studies, methylchloroisothiazolinone has been proven to be a bacterial mutagen.[3] The combination of methylisothiazolinone and methylchloroisothiazolinone (MI/MCI) is a well-documented cause of contact dermatitis in humans.[4][5][6]

Safety Data

A 1992 study found that when methylisothiazolinone and methylchloroisothiazolinone (MI/MCI) are administered orally, they are then excreted in urine and feces and mostly not stored in body tisuses.[7] However, when applied to the skin, up to 62% of the chemicals stayed bound to the application site 24 hours after exposure, and the chemicals bound to the skin had a 13.1-day half-life. Furthermore, the study found that "MI/MCI was moderately to highly toxic to rats, and highly toxic to rabbits when administered orally, and moderately toxic when applied dermally." The study tested the toxicity in rats, mice, rabbits, and dogs at various doses, applied orally or dermally. The study concluded that: "Methylisothiazolinone/Methylchloroisothiazolinone may be safely used in “rinse-off” products at a concentration not to exceed 15 ppm and in “leave-on” cosmetic products at a concentration not to exceed 7.5 ppm. The stated safe use concentration refers to a mixture containing 23.3% Methylisothiazolinone and 76.7% Methylchloroisothiazolinone."

Industry Influence

A number of major brands of personal care products contain methylchloroisothiazolinone (see below), and thus, industry has a stake in how the chemical is perceived, researched, and regulated. A study published in 1999 reassessed the safety of the two chemicals and concluded that concentrations of MI/MCI up to 15ppm in rinse-off products pose little risk of contact dermatitis to humans.[8] However, this study was conducted by a researcher funded by Procter & Gamble, and Procter & Gamble was also consulted during the course of the study.

List of Products Containing Methylchloroisothiazolinone

The following products contain methylchloroisothiazolinone.[9]

Personal Care Products

  • Aussie: Shampoo, Conditioner
  • Avon: ANEW PURE O2 Daily Oxygen Facial Cleanser
  • Axe: Shampoo, Conditioner, Shower Gel
  • Bath & Body Works: Shower Gel-Flowering Herbs
  • Clairol: Herbal Essences, True Intense Color, Hydrience Permanent Hair Color, Natural Instincts for Men Haircolor, Natural Instincts Haircolor, Natural Instincts Loving Care, Non-Permanent Hair Color
  • Caress: Body Wash
  • Dep: Extra Super Control Water Based Gel, Root Boost Volumizer for Maximum Lift
  • Dove: Shampoo, Conditioner
  • Finesse: Shampoo, Conditioner
  • Freeman Botanicals: Shampoo, Natural Hair Care
  • Gillette: Deep Cleaning Shampoo, Complete Skincare Multi-Glide Shave Gel
  • Head and Shoulders: Dandruff Shampoo, 2 in 1 Dandruff Shampoo and Conditioner
  • Herbal Essences, Shampoo, Conditioner, 2 in 1 Shampoo Plus Conditioner
  • Infusium 23: Volumologie Conditioner, Moisturologie Conditioner
  • John Frieda: Conditioner, Color Glaze
  • LA Looks: Gelz Mousse Extra Super Hold and Body, Extra Super Hold
  • Lever 2000: Body Wash
  • Method: Hand Wash
  • Olay: Body Wash
  • Pantene Pro-V: Shampoo, Conditioner, 2 in 1 Shampoo and Conditioner, Deep Hydrating Treatment, Nourishing Moisture Replenishing Mask
  • Paul Mitchell: Tea Tree Special Shampoo
  • Physique: Shampoo, Conditioner
  • Revlon: High Dimension 10 Minute Permanent Haircolor, Colorist Expert Color and Glaze System, Colorsilk Permanent Color::
  • Salon Selectives: Shampoo, Conditioner
  • Suave: Shampoo, 2 In 1 Shampoo and Conditioner, Body Wash, Liquid Hand Soap
  • Zest: Body Wash

Pet Shampoos

  • Four Paws Bunny Bath Shampoo & Deodorizer
  • 8 in 1 Perfect Coat Select Antibacterial Deodorizing Shampoo
  • Khargosh Rabbit and Small Animal Shampoo

Other Products

  • Daily Defense 2 in 1 Shampoo + Conditioner for All Hair Types, Water Lily
  • GOJO Natural Orange Pumice Hand Cleaner
  • Happy Daisy Relaxing Bath Bubbles
  • Henry Company HE 124 Tree Cure
  • Jingles Spray Protein
  • Johnsons Kids, No More Bedhead Spray, Watermelon Madness
  • Pure Elements Structure Gel
  • Pure Elements Hydrating Conditioner-Dry, Permed
  • Simply Ivory Body Wash
  • Spray N Wash: Prewash Stain Remover (pump)

Articles and resources

Related SourceWatch articles


  1. Household Products Database, U.S. Department of Health and Human Services, Accessed September 8, 2010.
  2. Connor TH, Tee PG, Afshar M, and Connor KM, "Mutagenicity of cosmetic products containing Kathon", Environmental and molecular mutagenesis, 1996, Accessed September 10, 2010.
  3. Connor TH, Tee PG, Afshar M, and Connor KM, "Mutagenicity of cosmetic products containing Kathon", Environmental and molecular mutagenesis, 1996, Accessed September 10, 2010.
  4. KH Gardner, MD Davis, DM Richardson, and MR Pittelkow, "The hazards of moist toilet paper: allergy to the preservative methylchloroisothiazolinone/methylisothiazolinone", Archives of Dermatology, August 2010, Accessed September 10, 2010.
  5. Czarnobilska E, Obtulowicz K, Dyga W, Wsolek-Wnek K, Spiewak R., "Contact hypersensitivity and allergic contact dermatitis among school children and teenagers with eczema", Contact Dermatitis, May 2009, Accessed September 10, 2010.
  6. Lundov MD, Moesby L, Zachariae C, Johansen JD, "Contamination versus preservation of cosmetics: a review on legislation, usage, infections, and contact allergy", Contact Dermatitis, February 2009, Accessed September 10, 2010.
  7. "6 Final Report on the Safety Assessment of Methylisothiazolinone and Methylchloroisothiazolinone", International Journal of Toxicology, January 1992.
  8. John Fewings and T. Menne, "An update of the risk assessment for methylchloroisothiazolinone/methylisothiamlinone (MCUMI) with focus on rinse-off products", February 1999.
  9. Household Products Database, U.S. Department of Health and Human Services, Accessed September 8, 2010.

External resources

External articles