Methyisothiazolinone ●
TL;DR. This ingredient is a synthetic preservative used to control microbial growth in water-based formulas, especially rinse-off products. It is valued for broad-spectrum activity at very low concentrations.
What does Methyisothiazolinone do in a cosmetic formula?
This ingredient is a synthetic preservative used to control microbial growth in water-based formulas, especially rinse-off products. It is valued for broad-spectrum activity at very low concentrations.
Is Methyisothiazolinone clean?
From a clean-beauty perspective, this ingredient has major friction because it is a well-documented contact allergen. Many retailers and standards exclude it, and regulators restrict it tightly in rinse-off products while not allowing it in leave-on products in several markets.
Is Methyisothiazolinone sustainable?
This material is synthetic and not plant-derived. It is not known for bioaccumulation, but its biocidal purpose and aquatic-organism concerns make it less aligned with lower-impact formulation choices.
Is Methyisothiazolinone COSMOS-approved?
It is not permitted under COSMOS-natural or COSMOS-organic standards. Its synthetic origin, preservative mode of action, and sensitization profile make it a poor fit with Green Chemistry preferences for low-irritation, readily accepted preservation systems.
How does Methyisothiazolinone work chemically?
The molecule is a small sulfur- and nitrogen-containing ring compound with a reactive unsaturated carbonyl system that interferes with microbial enzyme function. Regulatory limits are very low, such as 0.0015% in rinse-off cosmetics in the EU, and it is not allowed there in leave-on cosmetic products.
Last updated 2026-05-14