Methylchloroisothiazolinone is a chemical compound, a chlorinated isothiazolinone, 4-isothiazolin-3-one. It is one of the most widespread chemical preservative components used in cosmetic products.

The name describes the structure of the molecule:

• Methyl indicates the presence of a methyl group, a functional group consisting of one carbon atom bonded to three hydrogen atoms.
• chloro refers to the presence of chlorine in the compound, an element that contributes to the antimicrobial properties of the preservative.
• isothiazolinone indicates that the compound belongs to the class of isothiazolinones, a family of preservatives known for their effectiveness against a wide range of microorganisms, including bacteria, fungi, and yeasts.

Raw Materials and Their Functions

• Isothiazolinone Compounds. The base compounds used in the synthesis of methylchloroisothiazolinone. These compounds act as antimicrobial agents.
• Chlorine. Used to chlorinate isothiazolinone, enhancing its preservative properties.
• Industrial Chemical Synthesis of Methylchloroisothiazolinone
• Synthesis. The process begins with the synthesis of isothiazolinone compounds, followed by their chlorination to form methylchloroisothiazolinone.
• Reaction Control. The synthesis and chlorination reaction is monitored to ensure it occurs correctly and the final product has the desired antimicrobial properties.
• Purification. After synthesis, methylchloroisothiazolinone is purified to remove impurities and by-products.
• Quality Control. The purified methylchloroisothiazolinone undergoes quality checks to ensure it meets the required standards. After quality control, it is packaged for use as a preservative in cosmetic and personal care products.

Form and Color

 Methylchloroisothiazolinone is typically a liquid. This compound is usually colorless or very light in color.

What it is used for and where

Methylchloroisothiazolinone is a chemical compound used as a preservative in various products, including cosmetics, skincare products, and household cleaning products and  is used as a preservative for its ability to prevent the growth of microorganisms in products. However, it is also known for its potential to cause allergic reactions in some people, which is why its use is regulated in many countries.

Cosmetics

It is a restricted ingredient as  V/39 a Relevant Item in the Annexes of the European Cosmetics Regulation 1223/2009. Substance or ingredient reported: Mixture of 5-Chloro-2-methyl-isothiazol-3(2H)-one and 2-Methylisothiazol-3(2H)-one with magnesium chloride and magnesium nitrate.

Product Type, body parts    Rinse-off: Maximum concentration in ready for use preparation    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

Preservative. Any product containing organic, inorganic compounds, water, needs to be preserved from microbial contamination. Preservatives act against the development of harmful microorganisms and against oxidation of the product.

It is found in:

• soaps
• detergents
• creams
• shampoo
• glitter glue as make-up
• aerosol spray deodorants
• medical devices
• ironing water

Methylchloroisothiazolinone exercises function:

• preservative
• antioxidant
• fungicidal

Safety

This ingredient is effective in preventing the growth of bacteria, mold, and yeast, thereby helping to extend the shelf life of products. However, it is important to note that it can cause allergic reactions in some individuals, and its use is regulated in many countries.

However, its action caused an increase in cases of awareness in recent years with a widespread of dermatitis (1).

Methylchloroisothiazolinone studies

• Molecular Formula: C₄H₄ClNOS
• Molecular Weight: 149.592 g/mol
• UNII: DEL7T5QRPN
• CAS: 26172-55-4   137662-59-0  137086-87-4
• EC Number: 247-500-7

Synonyms:

• 5-Chloro-2-methyl-4-isothiazolin-3-one
• 3(2H)-Isothiazolone, 5-chloro-2-methyl-
• 5-chloro-2-methylisothiazol-3(2h)-one
• 5-Chloro-2-methyl-2H-isothiazol-3-one
• Chloromethylisothiazolinone
• 2,3-Dihydro-2-methyl-3-oxo-5-chloroisothiazole
• 5-Chloro-2-methyl-4-isothiazolin-3-one (CMI)
• 4-ISOTHIAZOLIN-3-ONE, 5-CHLORO-2-METHYL-
• 5-chloro-2-methyl-1,2-thiazol-3-one
• 5-chloro-n-methylisothiazolin-3-one
• N-Methyl-5-chloroisothiazolin-3-one
• Chloromethylisothiazolone
• 5-chloro-2-methyl-2h-isothiazolin-3-one
• 5-chloro-2-methyl-3(2H)-isothiazolinone
• 2-Methyl-5-chloroisothiazolin-3-one
• 5-chloro-2-methyl-isothiazol-3-one
• 2-Methyl-5-chloro-3-isothiazolone
• 5-Chloro-2-methyl-3-isothiazolone
• 5-chloro-2-methylisothiazolin-3-one
• 5-Chloro-2-methyl-isothiazol-3(2H)-one
• 5-chloro-N-methylisothiazolone
• 5-Chloro-2-methyl-3(2H)-isothiazolone
• 5-Chloro-2-methyl-4-isothiazolin-3-one solution
• 5-Chloride-2-Methyl-4-Isothiazoline-3-Ketone
• N-Methyl-5-chloroisothiazolone (5-Chloro-2-methyl-4-isothiazolin-3-one)
• CMIT
• Kathon CG 5243
• Bioace
• Kathon IXE
• CHEBI:53621

References________________________________________________________________________

(1) Contact allergy to methylchloroisothiazolinone/methylisothiazolinone in north-eastern Italy: a temporal trend from 1996 to 2016. Dusefante A, Mauro M, Belloni Fortina A, Corradin MT, Larese Filon F.  J Eur Acad Dermatol Venereol. 2019 May;33(5):912-917. doi: 10.1111/jdv.15453.

(2) Lichenoid contact dermatitis secondary to methylisothiazolinone (MI).
Raymond J, Konya J, Bakis-Petsoglou S.
JAAD Case Rep. 2016 Oct 6;2(5):380-383.