A preservative associated with allergic contact dermatitis and significant use restrictions.
Sources: 1MI, MIT
Not assessed
No pregnancy- or breastfeeding-specific assessment has been completed for this record. A cosmetic safety review is not a pregnancy rating.
Not assessed
Methylisothiazolinone
What it does
Controls microbial growth in permitted product uses; it is not a skin-treatment ingredient.
Sources: 1Good for
- Preservation in permitted products
How to use it
Use only within an appropriately formulated finished product. Preservatives are not a separate skincare application or a home treatment for infection.
Sources: 1Who should be careful
People with diagnosed MI allergy should avoid relevant products. Methylchloroisothiazolinone mixtures need separate identification.
Sources: 1Pairs well with
No supported pairings have been documented for this record.
Usage, safety and formulation details
Mechanism of action
Biocidal activity supports preservation, while sensitization risk depends on exposure and prior allergy.
Sources: 1Potential adverse effects
Irritation or allergic contact dermatitis may occur in susceptible users; inadequate preservation also carries risks.
Sources: 1Formulation considerations
Check current jurisdiction-specific rules for rinse-off versus leave-on use. Do not infer that any listed use is universally allowed.
Sources: 1Pregnancy and breastfeeding
Not assessed
No pregnancy- or breastfeeding-specific assessment has been completed for this record. A cosmetic safety review is not a pregnancy rating.
Safety tags
- Fragrance allergen
- Not assessed
Not separately assessed in this draft.
- Essential oil
- Not assessed
Not separately assessed in this draft.
- Drying alcohol
- Not assessed
Not separately assessed in this draft.
- May irritate sensitive skin
- Flagged
Potential concern depends on the product and exposure; this flag is not a prediction of every user's response.
Sources: 1
What remains uncertain
- Exact concentration, final pH and the full composition of any unprovided finished product
Clinical evidence and research
Clinical evidence
Evidence for its main benefitNot assessed
The cited references support identity, formulation role or safety context. No standalone clinical efficacy rating has been completed for the main benefit in this draft.
Sources: 1Regulation and ingredient label names
Regulatory information
European Union
SCCS methylisothiazolinone sensitization opinion
A leave-on versus rinse-off distinction is critical. Verify the current Annex V restriction and concentration; an assessment is not universal permission for every use.
Sources: 1Names on ingredient lists
methylisothiazolinone
Chemical identity and molecular structure
Chemical information
Chemical structure
| Detail | Value | Source |
|---|---|---|
| PubChem CID | 39800 | PubChem compound 39800: chemical identity |
| molecular formula | C4H5NOS | PubChem compound 39800: chemical identity |
| molecular weight | 115.16 g/mol | PubChem compound 39800: chemical identity |
| iupac name | 2-methyl-1,2-thiazol-3-one | PubChem compound 39800: chemical identity |
Content updated 9 November 2026.
Sources (2)
Scientific sources
- SCCS: Methylisothiazolinone sensitization assessmentscientific opinion
- PubChem compound 39800: chemical identitychemical identity
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