Methylisothiazolinone
MIT · Methylchloroisothiazolinone · MCI
What it is
A broad-spectrum antimicrobial preservative. MIT (2-methyl-4-isothiazolin-3-one) and MCI (chloromethylisothiazolinone) are commonly used together in a 3:1 ratio (branded Kathon CG).
In this product: Antimicrobial preservative.
Dose & route, what actually matters
Dermal. Sensitization risk is highest with leave-on products; rinse-off exposure is brief, which is why the 15 ppm limit for shampoos is considered acceptable. Already-sensitized individuals can react to rinse-off products too.
EUROPEAN UNION
MIT is BANNED in all leave-on cosmetics in the EU (since 2017, Commission Regulation (EU) 2017/1224). Permitted in rinse-off products (shampoos) at maximum 15 ppm (0.0015%) under Commission Regulation (EU) No 1003/2014 / Annex V/39. The surge in use as a paraben replacement correlated with a documented contact sensitization epidemic across Europe.
UNITED STATES
No restriction on MIT in cosmetics, leave-on or rinse-off. No federally mandated concentration cap.
The evidence
SCCS/1521/13 (December 2013): 'Current clinical data indicate that 100 ppm MI in cosmetic products is not safe for the consumer. For leave-on cosmetic products (including wet wipes), no safe concentrations of MI for induction of contact allergy or elicitation have been adequately demonstrated.'
regulatory · 2013 · source
Commission Regulation (EU) 2017/1224 banned MIT from all leave-on cosmetics; Commission Regulation No 1003/2014 restricted MCI/MIT to 15 ppm in rinse-off products.
regulatory · 2017 · source
California Prop 65: Not listed.
How to avoid it
Check for Methylisothiazolinone or Methylchloroisothiazolinone (or MI/MCI/Kathon CG) in the preservative system. Alternatives include sodium benzoate, benzyl alcohol, or preservative-free formulas.
Where it hides
Editorial analysis of publicly available regulatory and peer-reviewed sources. Not medical advice. We name our evidence and link it, including when an ingredient is fine.