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Methylisothiazolinone in skincare
ACDS Allergen of the Year 2013; EU-banned in leave-on products; restricted in rinse-off products; major sensitizer.
EU-banned in all leave-on cosmetics (since Feb 2017). Only permitted in rinse-off products (shampoos, shower gels) at max 0.01% (100 ppm). In rinse-off products, PM use has slightly less contact time concern than leave-in. The primary hazard is sensitization. Once sensitized, even trace amounts in any product (rinse-off or leave-on) can trigger reactions. Avoid in all leave-on formulations regardless of geography.
What it is
Methylisothiazolinone (MIT, MI) is a broad-spectrum isothiazolinone biocide preservative that became widely used as a 'paraben-free' alternative starting in the 2000s. Triggering a European epidemic of allergic contact dermatitis, peaking around 2013–2015. The American Contact Dermatitis Society named it Allergen of the Year for 2013. EU SCCS concluded it is a strong sensitizer. Regulatory actions: EU banned MIT in all leave-on cosmetics (Commission Regulation EU 2016/1198, effective Feb 2017); restricted in rinse-off products to 0.01% (100 ppm) maximum. The mixture with Methylchloroisothiazolinone (MCI/MI, Kathon CG) is banned from EU leave-on products (since 2014) and restricted to 0.0015% (15 ppm) in rinse-off products. US: FDA classifies it as a standardized chemical allergen; CIR considers it safe at current rinse-off concentrations but sensitization in predisposed individuals remains. In vitro neurotoxicity studies showed concerns at high concentrations. Not considered relevant at cosmetic use levels but adds to precautionary avoidance. If sensitized, even trace amounts can trigger systemic reactions.
The facts
| Category | Preservative (Isothiazolinone) |
| Typical use | Morning and evening |
| Concentration YARAI treats as a full dose | 0.0015% |
| EU maximum permitted concentration | 0.0015% (0.0015% (of a mixture in the ratio 3:1 of 5 -Chloro-2-methyl-isothiazol-3(2H)-one and 2-Methylisothiazol-3(2H)-one) |
| EU Cosmetics Regulation annex | II |
| EU status | prohibited |
| EU and US differ | FDA has no concentration limit. Required only to be listed on labels. Considered safe in rinse-off at low concentrations by US standards. |
Why the amount matters, not just the presence
Most ingredient checkers tell you whether something is in the bottle. That is a smaller question than it sounds. Methylisothiazolinone at 0.0015% and methylisothiazolinone at a trace level are not the same ingredient in any way that affects your skin.
An ingredient list is ordered by quantity, so position carries real information. YARAI reads that position and scores accordingly, which is why the same ingredient can land differently in two different products.
The honest limit: a list gives order, not percentages. Estimating concentration from position is an estimate. It is a better estimate than ignoring position, and it is still an estimate. We would rather tell you that than let a number look more certain than it is.
Regulatory status
Banned in leave-on cosmetics in EU (Annex II) since 2017 due to skin sensitisation. Still permitted in rinse-off at 0.0015%.
Common questions
What does methylisothiazolinone do in a skincare product?
ACDS Allergen of the Year 2013; EU-banned in leave-on products; restricted in rinse-off products; major sensitizer.
How much methylisothiazolinone should a product contain?
YARAI treats 0.0015% as a full dose for this ingredient. Below that, the ingredient is present but is scored as contributing less. An ingredient list gives you the order of ingredients, not their percentages, so this is an estimate read from position rather than a measurement.
Is methylisothiazolinone restricted in the EU?
The EU Cosmetics Regulation permits this ingredient up to 0.0015% in leave-on cosmetics, listed under II. 0.0015% (of a mixture in the ratio 3:1 of 5 -Chloro-2-methyl-isothiazol-3(2H)-one and 2-Methylisothiazol-3(2H)-one
When should I use methylisothiazolinone?
EU-banned in all leave-on cosmetics (since Feb 2017). Only permitted in rinse-off products (shampoos, shower gels) at max 0.01% (100 ppm). In rinse-off products, PM use has slightly less contact time concern than leave-in. The primary hazard is sensitization. Once sensitized, even trace amounts in any product (rinse-off or leave-on) can trigger reactions. Avoid in all leave-on formulations regardless of geography.
Check your own products
Point your camera at a product. YARAI identifies it from the label, finds that product's full ingredient list from published sources, and scores it. No barcode and no box needed, which is how it handles imported and small-brand products.
Concern level, category and thresholds on this page are read directly from the same data the YARAI app scores with, so this page and the app cannot disagree. EU figures cite Regulation (EC) No 1223/2009. Last built 2026-09-09. Nothing here is medical advice.