“Methylchloroisothiazolinone?”Here!MCI (often paired with MI, sold together as Kathon CG)
Appears in 4 scanned products.
In personal care
A synthetic preservative from the isothiazolinone family, almost always used in combination with a related compound, methylisothiazolinone. Together they are added in very small amounts to stop bacteria and fungi from growing in water-based products.
Why it’s used
It is an effective, broad-spectrum preservative that works at low concentrations, which made it popular in shampoos, conditioners, and other water-heavy formulas that would otherwise spoil.
What the evidence says
This is one of the better-documented cases of a cosmetic ingredient causing contact allergy. Rising rates of allergic skin reactions through the 2000s and 2010s led the EU Scientific Committee on Consumer Safety to review the evidence and recommend restrictions; the EU subsequently banned it from leave-on products entirely and capped its concentration in rinse-off products. The concern is sensitization and allergic contact dermatitis, not systemic toxicity.
Context
Risk is strongly tied to contact time: leave-on use (lotions, creams) carries meaningfully higher risk of sensitization than rinse-off use (shampoo, body wash), which is why regulators drew the line exactly there. Where still permitted, it is capped at low parts-per-million concentrations.
Rumors
Methylchloroisothiazolinone is one of the most common causes of cosmetic contact allergy.
Supports — suggestivehealth and safety evidence
Studied in: patients referred for diagnostic patch testing for suspected contact dermatitis.
Measured as a biomarker.
- Epidemic of Isothiazolinone Allergy in North America: Prevalence Data From the North American Contact Dermatitis Group, 2013-2014. (Peer-reviewed) · Funding not checked
Who’s saying this
- Campaign for Safe Cosmetics — an advocacy group: campaigns for safer cosmetics; program of Breast Cancer Prevention Partners
How we know who this is
- “The Campaign for Safe Cosmetics (CSC) leads the movement to make beauty and personal care products safer for all.” (their page)
- “CSC is a program of Breast Cancer Prevention Partners (BCPP) , a national science-based advocacy organization working to prevent breast cancer by eliminating environmental exposures linked to the disease.” (their page)
Where it shows up
and 3 more products