Methylisothiazolinone
molecular structure · PubChem
AKA: 2682-20-4, 2-Methyl-4-isothiazolin-3-one, 2-Methyl-3(2H)-isothiazolone, 2-Methyl-4-isothiazoline-3-one, N-methylisothiazolone, 3(2H)-Isothiazolone, 2-methyl-3-isothiazolone, N-methylisothiazolin-3-one, Neolone 950
Allergen Warning
⚠️ MI/MCI Preservative
Synthetic
Preservative
Medicated Active
Not Clean
The Expert Panel for Cosmetic Ingredient Safety concluded that Methylisothiazolinone is safe for use in rinse-off cosmetic products at concentrations up to 100 ppm (i.e. 0.01%) and safe in leave-on cosmetic products when they are formulated to be non-sensitizing, which may be determined based on a QRA or similar methodology.
Solubility Solubility in: acetonitrile 78.6; methanol 79.1; hexane 2.371; xylenol 15.65 (g/100 mL)
Formula
C4H5NOS
Mol. Weight
115.16
CAS #
2682-20-4
Form
Liquid
State
NKRA; Liquid
Functions
Preservative
Keeps your product from growing bacteria, mold, or yeast. Without these, that jar of cream becomes a petri dish in about a week.
Preserves Formula
Prevents microbial growth
Traditional Use
Synthesized in the 1970s as a preservative and biocide for cosmetics, personal care, and industrial products. Designed to be a more stable alternative to earlier isothiazolinone preservatives.
EWG
7
CIR
Safe as used
Pregnancy
Caution
Restricted By
CIR Safety Findings
Not a Sensitizer
medical-approval
all-shades-safe
Concentration Guide
0.01%
0%0%
Reg. Limit
EU regulatory limit: 0.01%. Source: EU Cosmetics Regulation (EC) 1223/2009, Annex V (Preservatives), Entry 57.
Regulatory Agencies
🧂Conflict of interest.
Skin Types
●all-skin-types
Best For
General
Pregnancy & Breastfeeding Safe
Caution
The paper trail
🔬Peer-reviewed1 paper →
⚖️Regulatory1 listing →
🛡️Safety-assessed2 reviews →
Counts, not a verdict. A listing isn't a study. The trail, you decide.
Verified Jun 2026 · 🧪 = conflict
Data: PubChem · CosIng · EWG · CIR