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Methylisothiazolinone

Strong biocide preservative. One of the most frequent contact allergens of the past decade – in the EU it is restricted to rinse-off products at very low concentrations.

Evidence by route

D

Topical application

The European SCCS confirmed: in leave-on formulas MIT drives an epidemic of contact sensitization. Rinse-off products allow only microdoses, and sensitive skin should avoid it entirely.

How to read tiers A–F
  • DNo data, or very weak or conflicting data

Tolerability and safety

Irritation potential
High
Allergen risk
High
Pregnancy
Caution
Use with caution
Sensitive, Dry

About this ingredient

Methylisothiazolinone (MI) is a synthetic preservative. Used alone or in a 1:3 blend with methylchloroisothiazolinone (MCI) (Kathon CG). Mechanism. Inhibits respiratory chain enzymes in microorganisms via covalent binding to thiol groups. Effective against bacteria and fungi. Where applied. Rinse-off products only in the EU since 2017. Before 2013 widely used in leave-on. After the 2010–2013 contact dermatitis epidemic the EU SCCS revised regulation. Maximum concentration – 0.0015% (15 ppm). Evidence base. Epidemiology. According to NACDG and ESSCA, MI became the number one contact allergen in 2013 in Europe and the US. Sensitization rates rose from 0.1% to 5–10% over 5 years. The American Contact Dermatitis Society named MI "Allergen of the Year 2013". Safety. SCCS confirmed safety in rinse-off products at 15 ppm. In sensitized patients – severe contact dermatitis with face and hand eczema, sometimes chronic. EU labeling required since 2017. Pregnancy and lactation – use with caution. At approved concentrations systemic absorption is minimal. Strict avoidance in patients with confirmed sensitization. Alternatives – phenoxyethanol, sodium benzoate, benzyl alcohol, pentylene glycol.

Frequently asked questions

Is Methylisothiazolinone safe during pregnancy?

Methylisothiazolinone should be used with caution during pregnancy. Consulting a dermatologist or OB-GYN is advisable.

What skin types is Methylisothiazolinone for?

Use with caution in: sensitive, dry.

Can Methylisothiazolinone irritate the skin?

Yes, Methylisothiazolinone has high irritation potential. Start at low concentrations, introduce gradually, and always use SPF during the day.

Can Methylisothiazolinone cause an allergic reaction?

Methylisothiazolinone has high allergen potential. Perform a patch test on the inner forearm 24 hours before facial application.

What is Methylisothiazolinone and what does it do in cosmetics?

Strong biocide preservative.

What's the INCI name for Methylisothiazolinone?

The INCI name is Methylisothiazolinone. It may also appear as: MI, MIT, Kathon MI.

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