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Methylchloroisothiazolinone
IUPAC name	5-Chlor-2-methyl-4-isothiazolin-3-one
Other names	Chloromethylisothiazolinone; Chloromethylisothiazolone; Methylchloroisothiazolinone; Methylchloroisothiazolone;CMI; CMIT; MCI
Identifiers
CAS number	26172-55-4
SMILES	S1N(C)C(=O)C=C1[Cl]
Properties
Molecular formula	C4H4ClNOS
Molar mass	149.59 g/mol
Appearance	colorless liquid
Density	1.02 g/cm³, liquid
Melting point	?°C (? K)
Boiling point	?°C (? K)
Solubility in water	miscible with
Viscosity	? cP at ?°C
Hazards
R-phrases	R23/24/25 R34 R43 R50/53
S-phrases	Template:S(2) S26 S28 Template:R36/37/39 S45 S60 S61
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references

Methylchloroisothiazolinone (5-chloro-2-methyl-4-isothiazolinon-3-one) is a preservative with antibacterial and antifungal effects within the group of isothiazolinones. It is effective against gram-positive and gram-negative bacteria, yeast and fungi.

It is found in many water-based personal care products and cosmetics.^[1] It is also used in glue production, detergents, paints, fuels and other industrial processes. Methylchloroisothiazolinone is known by the registered tradename Kathon CG when used in combination with methylisothiazolinone.^[2]

It can be used in combination with alcohols and other long-chain organics in compounds such as methylchloroisothiazolinone ethylparaben benzalkonium chloride or methylchloroisothiazolinone 2-bromo-2-nitropropane-1,3-diol benzalkonium chloride.

It was first used in cosmetics in the 1970s. In high concentrations it can cause chemical burns and it is a skin and membrane irritant and so it was largely removed from most cosmetic products except for those with only short duration skin contact such as rinse-offs. Its inclusion in certain forms makes it more acceptable to sensitive users, so it can be found in cosmetic creams and lotions which require skin contact. In the US accepted concentrations are 15 ppm in rinse-offs and 8 ppm in other cosmetics^{[citation needed]}.

Like a number of other common cosmetics ingredients, methylchloroisothiazolinone has been considered to be a carcinogen. Methylchloroisothiazolinone is an allergen.^[3]

1. ^ Reinhard et al.: "Preservation of products with MCI/MI in Switzerland". Contact Dermatitis. 2001 Nov;45(5):257-64. PMID 11722483
2. ^ Knudsen BB, Menne T: "Kathon CG--a new contact sensitizing preservative". Ugeskr Laeger. 1990 Mar 5;152(10):656-7. PMID 2321281
3. ^ Zoller L, Bergman R, Weltfriend S. Preservatives sensitivity in Israel: a 10-year overview (1995-2004). Contact Dermatitis. 2006 Oct;55(4):227-9. PMID 16958921

• Household products containing Chlormethylisothiazolinone