No known benefits

Methylisothiazolinone at a glance

  • Also referred to as MI, or Kathon CG (when in an ingredient blend)
  • Used as a preservative when combined with methylchloroisothiazolinone
  • Is a well-known skin sensitizer
  • Limited use in leave-on products at 7.5 ppm (parts per million) and rinse-off products at 15 ppm when in a blend

Methylisothiazolinone description

Preservative that’s generally recommended for use only in rinse-off products such as cleansers or shampoos. Methylisothiazolinone is known to be sensitising when used in leave-on products. Its use in both rinse-off and leave-on cosmetics products is restricted to low amounts as a means to avoid sensitivity while maintaining its efficacy as a preservative, but even in the low amount permitted (0.01%) has raised questions about it being more sensitising than most other preservatives.

Methylisothiazolinone references

  • JAMA Dermatology, January 2023, pages 267-274
  • International Journal of Toxicology, July-August 2021, pages 20S-33S
  • Anais Brasileiros de Dermatologia, Nov-Dec 2015, pages 912-914
  • British Journal of Dermatology, December 2011, pages 1,178-1,182

Peer-reviewed, substantiated scientific research is used to assess ingredients in this dictionary. Regulations regarding constraints, permitted concentration levels and availability vary by country and region.

Ingredient ratings


Proven and supported by independent studies. Outstanding active ingredient for most skin types or concerns.


Necessary to improve a formula's texture, stability, or penetration.


Generally non-irritating but may have aesthetic, stability, or other issues that limit its usefulness.


There is a likelihood of irritation. Risk increases when combined with other problematic ingredients.


May cause irritation, inflammation, dryness, etc. May offer benefit in some capability but overall, proven to do more harm than good.


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Not rated

We have not yet rated this ingredient because we have not had a chance to review the research on it.