Methylisothiazolinone (MIT) is a synthetic preservative from the isothiazolinone family, widely used as an antimicrobial and antifungal agent across various industries.
Due to its strong bactericidal and fungicidal properties, MIT effectively prevents the growth of microorganisms in chemical and consumer products, thereby extending their shelf life and stability.

Chemical Information

Chemical Name: Methylisothiazolinone
Chemical Formula: C₄H₅NOS
Molar Mass: 115 g/mol (corrected from 15 g/mol)
CAS Number: 2682-20-4
Molecular Structure: Isothiazolinone ring substituted with a methyl group at the 2-position, which contributes to its antimicrobial activity and molecular stability.

Physical and Chemical Properties

Property	Typical Value / Range
Appearance	Clear to pale yellow liquid
Odor	Mild, characteristic odor
Solubility	Miscible with water and polar organic solvents
pH Stability Range	Stable between pH 4 – 9
Boiling Point	~155 – 160°C
Vapor Pressure (25°C)	Very low (< 0.1 mmHg)
Key Feature	Broad-spectrum antimicrobial activity at very low concentrations (few ppm)

Applications of Methylisothiazolinone

1. Personal Care and Cosmetic Products

Used as a preservative in shampoos, conditioners, lotions, creams, body washes, and other personal care formulations.

Under EU Cosmetics Regulation, the maximum allowed concentration in rinse-off products is 0.0015% (15 ppm).
Not permitted in leave-on cosmetic products in the EU due to sensitization concerns.

2. Detergent and Cleaning Products

Applied as an antimicrobial preservative in dishwashing liquids, laundry detergents, disinfectants, and household cleaners.

3. Paints, Adhesives, and Resins

Prevents microbial contamination and spoilage in water-based paints, adhesives, and polymer emulsions.

4. Industrial and Technical Uses

Used in cooling water systems, metalworking fluids, lubricants, and industrial process liquids to inhibit microbial growth.

Advantages

Highly effective at very low concentrations, offering economic efficiency.
Broad-spectrum activity against both bacteria and fungi.
Can be combined with other preservatives (e.g., Methylchloroisothiazolinone – CMIT) to enhance efficacy and stability.
Extends the shelf life of formulations without significantly affecting product performance.

Limitations

May cause skin sensitization or contact dermatitis in sensitive individuals.
Overuse or high concentrations can irritate skin and eyes.
Regulatory restrictions apply under EU and FDA guidelines.
Increasing reports of allergic reactions have led to limitations or bans of MIT as a standalone preservative in many cosmetic formulations.

Safety and Handling

Aspect	Recommendation
Skin / Eye Contact	Avoid direct contact; wear chemical-resistant gloves, safety goggles, and protective clothing
Inhalation	Use in well-ventilated areas; avoid inhaling vapors or mists
Storage Conditions	Store in a cool, dry, well-ventilated place away from heat and direct sunlight
Permissible Concentration	Must comply with international regulations (typically ≤ 0.01% in cosmetic and personal care products)
Flash Point	> 100°C (approx.)
Environmental Hazards	Toxic to aquatic organisms (Aquatic Acute 1, H400 / Aquatic Chronic 2, H411 – per ECHA classification); disposal should follow local environmental regulations

Summary

Methylisothiazolinone (MIT) is a high-performance preservative providing effective protection against microbial contamination in both consumer and industrial formulations.
Despite its high efficacy and economic benefits, its potential for skin sensitization requires strict adherence to regulatory concentration limits and safe handling practices.