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Annex V Entry 39 28/09/2022

METHYLCHLOROISOTHIAZOLINONE AND METHYLISOTHIAZOLINONE

Mixture of 5-Chloro-2-methyl-isothiazol-3(2H)-one and 2-Methylisothiazol-3(2H)-one with magnesium chloride and magnesium nitrate

METHYLCHLOROISOTHIAZOLINONE AND METHYLISOTHIAZOLINONE appears in Annex V as a positive-list preservative entry for EU cosmetics. Maximum concentration in this record: 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.

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Permitted preservative— Annex V, EU Regulation 1223/2009
Max conc.: 0.0015%
Entry: 39

Reading this entry

MCI/MI is permitted only in rinse-off products, at 0.0015% of a fixed 3:1 mixture — and it may not be combined with methylisothiazolinone used on its own under entry 57.

  • 0.0015%, and only in rinse-off products.
  • The limit is on a mixture in a fixed 3:1 ratio of methylchloroisothiazolinone to methylisothiazolinone.
  • Methylisothiazolinone alone is entry 57, also 0.0015% and also rinse-off only.
  • The two entries cannot both be used in one product: the blend and the single substance are alternatives, not additions.

This is one of the lowest limits in Annex V, and the reason is well documented: the isothiazolinones are potent contact sensitisers, and the restrictions were tightened over several amendments as the scale of induced allergy became clear. Leave-on use was removed entirely; what remains is rinse-off at 0.0015%.

Two details are easy to lose. The limit applies to a mixture in the ratio 3:1 — three parts methylchloroisothiazolinone to one part methylisothiazolinone — so it is not a permission for either substance at that concentration, but for that blend. And methylisothiazolinone on its own is a different entry, number 57, with its own 0.0015% rinse-off limit.

A formulator cannot use both. The regulation treats the blend and the single preservative as alternatives, and a product containing MCI/MI cannot also carry MI under the separate entry to reach a higher total.

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Chemical identity and properties

PubChem 2D chemical structure for CAS 26172-55-4
CAS 26172-55-4PubChem CID 33344

5-Chloro-2-methyl-4-isothiazolin-3-one

Chloromethylisothiazolinone is a 1,2-thiazole that is 4-isothiazolin-3-one bearing a methyl group on the nitrogen atom and a chlorine at C-5. It is a powerful biocide and preservative and is the major active ingredient in the commercial product KathonTM. It has a role as an antimicrobial agent, a xenobiotic and an environmental contaminant. It is an organochlorine compound and a member of 1,2-thiazoles. It is functionally related to a methylisothiazolinone. — ChEBI

IUPAC name
5-chloro-2-methyl-1,2-thiazol-3-one
Molecular formula
C4H4ClNOS
Molecular weight
149.60 g/mol
Exact mass
148.9702126 Da
XLogP3
0.9
Topological polar surface area
45.6 Ų
Hydrogen-bond donors
0
Hydrogen-bond acceptors
2
Covalent units
1
Defined stereocentres
0

Also known as

MethylchloroisothiazolinoneCMIT5-Chloro-2-methyl-3(2H)-isothiazolone5-Chloro-2-methyl-3-isothiazoloneKathon CG 52433(2H)-Isothiazolone, 5-chloro-2-methyl-5-chloro-N-methylisothiazolone5-chloro-2-methylisothiazolin-3-one
16 more reported names
5-chloro-n-methylisothiazolin-3-oneHS 818n-methyl-5-chloroisothiazoloneDEL7T5QRPN4-ISOTHIAZOLIN-3-ONE, 5-CHLORO-2-METHYL-N-Methyl-5-chloroisothiazolin-3-one5-chloro-2-methyl-3(2H)-isothiazolinoneHS-818RefChem:818544247-500-7Chloromethylisothiazolinone5-chloro-2-methylisothiazol-3(2h)-one5-Chloro-2-methyl-2H-isothiazol-3-one5-chloro-2-methyl-isothiazol-3-one5-Chloro-2-methyl-4-isothiazolin-3-one (CMI)5-chloro-2-methyl-4-isothiazoline-3-one
Open full PubChem recordPubChem annotations3D structure image
External database identifiers

Retrieved from NIH PubChem on 2026-09-02 by checksum-valid CAS matching. Chemical properties do not replace the regulatory decision on this page.

PubChem 2D chemical structure for CAS 2682-20-4
CAS 2682-20-4PubChem CID 39800

Methylisothiazolinone

Methylisothiazolinone is a 1,2-thazole that is 4-isothiazolin-3-one bearing a methyl group on the nitrogen atom. It is a powerful biocide and preservative and is the minor active ingredient in the commercial product KathonTM. It has a role as an antimicrobial agent, an antifungal agent and an antifouling biocide. — ChEBI

IUPAC name
2-methyl-1,2-thiazol-3-one
Molecular formula
C4H5NOS
Molecular weight
115.16 g/mol
Exact mass
115.00918496 Da
XLogP3
0.0
Topological polar surface area
45.6 Ų
Hydrogen-bond donors
0
Hydrogen-bond acceptors
2
Covalent units
1
Defined stereocentres
0

Also known as

2-Methyl-4-isothiazolin-3-one2-Methyl-3(2H)-isothiazolone2-Methyl-4-isothiazoline-3-oneN-methylisothiazolone3(2H)-Isothiazolone, 2-methyl-2-methyl-3-isothiazolonen-methylisothiazolin-3-oneNeolone 950
16 more reported names
2-methyl-1,2-thiazol-3(2H)-one229D0E1QFA2-Methyl-4-isothiazoline-3-ketoneCHEBI:53620methyl-isothiazolinonemethylisothiazolidinoneRefChem:158243220-239-6methylisothiazolone2-methylisothiazol-3(2h)-one2-METHYL-2H-ISOTHIAZOL-3-ONEMITNeoloneN-Methyl-3-oxodihydroisothiazole2-Methyl-4-isothiazolin-3-one (MI)Kordek 50
Open full PubChem recordPubChem annotations3D structure image
External database identifiers

Retrieved from NIH PubChem on 2026-08-31 by checksum-valid CAS matching. Chemical properties do not replace the regulatory decision on this page.

PubChem 2D chemical structure for CAS 55965-84-9
CAS 55965-84-9PubChem CID 41679

Kathon

IUPAC name
5-chloro-2-methyl-1,2-thiazol-3-one;2-methyl-1,2-thiazol-3-one
Molecular formula
C8H9ClN2O2S2
Molecular weight
264.8 g/mol
Exact mass
263.9793976 Da
Topological polar surface area
91.2 Ų
Hydrogen-bond donors
0
Hydrogen-bond acceptors
4
Covalent units
2
Defined stereocentres
0

Also known as

Kathon 886Kathon LX15O9QS218W3(2H)-Isothiazolone, 5-chloro-2-methyl-, mixt. with 2-methyl-3(2H)-isothiazoloneKathon 886 biocideMBC-215RefChem:151011Kathon biocide
16 more reported names
Kathon CGKathon 886MWZonen FProClin 3002-Methylisothiazol-3(2H)-one compound with 5-chloro-2-methylisothiazol-3(2H)-one(14%in H2O)C8H9ClN2O2S22-Methylisothiazol-3(2H)-one compound with 5-chloro-2-methylisothiazol-3(2H)-oneBio-Perge2-Methylisothiazol-3(2H)-one 5-chloro-2-methylisothiazol-3(2H)-one (1:1)5-Chloro-2-methyl-3(2H)-isothiazolone mixt. with 2-methyl-3(2H)-isothiazoloneKathon WTMicrocide IIISomacide RSLegend MK3(2H)-Isothiazolone, 5-chloro-2-methyl-, mixt. with2-methyl-3(2H)-isothiazoloneOTHER CA INDEX NAMES:3(2H)-Isothiazolone, 2-methyl-, mixt. contg.Kathon CG/ICP II
Open full PubChem recordPubChem annotations3D structure image
External database identifiers

Retrieved from NIH PubChem on 2026-09-02 by checksum-valid CAS matching. Chemical properties do not replace the regulatory decision on this page.

Record details

Maximum concentration

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

Product type

Rinse-off

INCI glossary name

METHYLCHLOROISOTHIAZOLINONE AND METHYLISOTHIAZOLINONE

Chemical name

Mixture of 5-Chloro-2-methyl-isothiazol-3(2H)-one and 2-Methylisothiazol-3(2H)-one with magnesium chloride and magnesium nitrate

Chemical / IUPAC name

Mixture of 5-Chloro-2-methyl-isothiazol-3(2H)-one and 2-Methylisothiazol-3(2H)-one with magnesium chloride and magnesium nitrate

Regulatory information

Regulation

(EC) 2014/1003

See every entry this act set

SCCS opinions

  • Opinion concerning Update of Entry no 39 of Annex VI to Directive 76/768/EEC on Cosmetic Products: Mixture of 5-Chloro-2-methyl-isothiazolin-3(2H)-one and 2-Methylisothiazolin-3(2H)-one
  • Clarification of the SCCNFP Opinion on the Update of Entry no. 39 of Annex VI to Directive 76/768/EEC on Cosmetic Products: Mixture of 5-Chloro-2-methyl-isothiazolin-3(2H)-one and 2-Methylisothiazolin-3(2H)-one
  • Opinion on Mixture of 5-chloro-2-methyl-isothiazolin-3(2H)-one and 2-methyl-isothiazolin-3(2H)-one
  • Opinion on Methylisothiazolinone (P94) (Sensitisation only)
  • Submission II

Identified ingredients

Key data

CAS
26172-55-4, 2682-20-4, 55965-84-9
EC
247-500-7, 220-239-6
Annex
V
Entry number
39

Inventory links for METHYLCHLOROISOTHIAZOLINONE AND METHYLISOTHIAZOLINONE

Direct matches are limited for this record, so nearby entries from Annex V are shown as well.

Annex V 38
Nearby record in the same annex

O-CYMEN-5-OL

CAS: 3228-02-2
EC: 221-761-7
Annex V 34
Nearby record in the same annex

BENZYL ALCOHOL

CAS: 100-51-6
EC: 202-859-9
Annex V 33
Nearby record in the same annex

DMDM HYDANTOIN

CAS: 6440-58-0
EC: 229-222-8

What Annex V means for METHYLCHLOROISOTHIAZOLINONE AND METHYLISOTHIAZOLINONE

METHYLCHLOROISOTHIAZOLINONE AND METHYLISOTHIAZOLINONE is an approved preservative listed in Annex V of EU Cosmetics Regulation 1223/2009. Only substances on this positive list may be used as cosmetic preservatives in the EU.

Each preservative entry specifies maximum permitted concentrations and applicable product scope. Concentrations must not exceed the listed maximum. Some preservatives require warning statements on the product label.

This record is linked to 2 CosIng inventory ingredients for name and identifier cross-reference. The page also surfaces 12 related annex records with overlapping identifiers, annex logic or naming patterns.

Compliance checklist

  • Use concentration must not exceed: 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
  • Verify the preservative is effective at the permitted concentration for your matrix.

Frequently asked questions

Yes. METHYLCHLOROISOTHIAZOLINONE AND METHYLISOTHIAZOLINONE is listed in Annex V of EU Cosmetics Regulation 1223/2009 as a permitted preservative. It may be used in cosmetics up to the maximum concentration specified above, within the permitted product scope.

CAS 26172-55-4, 2682-20-4, 55965-84-9 is the unique numerical identifier assigned to METHYLCHLOROISOTHIAZOLINONE AND METHYLISOTHIAZOLINONE by the Chemical Abstracts Service. In cosmetic compliance work, the CAS number is used to cross-reference the substance across regulatory databases, raw material specifications and safety assessment reports. Multiple EU annex entries may share the same CAS number if the same substance appears under different conditions or in different annexes.

The maximum concentration of 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 applies to the concentration of the substance in the ready-to-use cosmetic product. When the substance is supplied as part of a blend or mixture, the calculation must account for the contribution of all sources in the formulation. The combined concentration must not exceed the stated limit.

Use the INCI Checker tool on this site to paste your full ingredient list (INCI) and scan it against all Annex II–VI entries. The tool highlights any ingredients that match restricted, prohibited or allergen-flagged records. This is useful for rapid compliance screening of finished product formulas or raw material declarations.
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Source note for Annex V record METHYLCHLOROISOTHIAZOLINONE AND METHYLISOTHIAZOLINONE

This page summarizes one Annex V record for METHYLCHLOROISOTHIAZOLINONE AND METHYLISOTHIAZOLINONE from public European Commission cosmetic materials and adds linked inventory or identifier matches when available.

Use this record page to review Annex V conditions for METHYLCHLOROISOTHIAZOLINONE AND METHYLISOTHIAZOLINONE, but confirm any final regulatory decision against the current official annex wording and source files.

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