CosmeticBet
Preservatives

Methylisothiazolinone

INCI: METHYLISOTHIAZOLINONE · also MI, MIT

The preservative that caused an allergy epidemic.

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C4H5NOS115.16 g/mol
sulfuroxygennitrogencarbonhydrogen
3D shape from PubChem 39800

How common

All products4.4%
In conditioners20%
In shampoos18%
In hair colours14%

645 of 14,784 products with a full ingredient list in Open Beauty Facts; No. 64 of all the names found on their labels.

What it is

  • A strong preservative.

    SourceHide
    which functions as a preservative in cosmetics[1] US Cosmetic Ingredient Review expert panel · 2021 · open source

Why it is in products

  • To stop microbes growing in the product: that is what a preservative is for.

    2 sourcesHide
    The preservative methylisothiazolinone (MI)[2] Review · 2013 · open source
    ‘preservatives’ means substances which are exclusively or mainly intended to inhibit the development of micro-organisms in the cosmetic product[3] EU law · 2026 · open source

Downsides and safety

  • It caused an unprecedented epidemic of skin allergy in Europe, mostly from leave-on products and mostly in women. It was named “Contact Allergen of the Year” for 2013 by the American Contact Dermatitis Society.

    Well established3 sourcesHide
    Methylisothiazolinone (MI) has caused an unprecedented epidemic of contact allergy in Europe and elsewhere.[4] Study · 2020 · open source
    This resulted in an epidemic of allergic contact dermatitis to MI, mainly affecting women exposed to leave-on cosmetics.[5] Study · 2021 · open source
    The preservative methylisothiazolinone (MI) is the American Contact Dermatitis Society Contact Allergen of the Year for 2013.[2] Review · 2013 · open source

  • After the EU limits, allergy among people tested in 11 countries halved between 2015 and 2017.

    Well established2 sourcesHide
    The prevalence of MI contact allergy decreased by 50% from 2015 to 2017.[4] Study · 2020 · open source
    at 14 centres in 11 European countries[4] Study · 2020 · open source

Where it works

Works insidethe product

It works in the product, keeping it free of germs. The allergy, when it happens, is in the skin.

SourceHide
‘preservatives’ means substances which are exclusively or mainly intended to inhibit the development of micro-organisms in the cosmetic product[3] EU law · 2026 · open source

Rules

European Union

  • Banned in leave-on products since 12 February 2017, because EU scientists found no safe level for them. In rinse-off products it is allowed up to 0.0015% (15 ppm).

    4 sourcesHide
    this substance should therefore be banned in leave-on products[6] EU law · 2016 · open source
    From 12 February 2017 only cosmetic products which comply with this Regulation shall be placed and made available on the Union market.[6] EU law · 2016 · open source
    For leave-on cosmetic products (including 'wet wipes'), no safe concentrations of MI for induction of contact allergy or elicitation have been adequately demonstrated.[7] EU Scientific Committee on Consumer Safety · 2015 · open source
    Methylisothiazolinone ( 18 ) 2682-20-4 220-239-6 Rinse-off products 0,0015 %[3] EU law · 2026 · open source

United States

  • Not on the FDA’s list of prohibited or restricted cosmetic ingredients. In the US, cosmetics and their ingredients (other than colour additives) don’t need FDA approval before sale.

    SourceHide
    Under U.S. law, cosmetic products and ingredients, other than color additives, do not need FDA approval before they go on the market[8] US Food and Drug Administration · open source
    We searched the FDA’s list of prohibited and restricted cosmetic ingredients: no entry.open the list

  • Looser than the EU: the US expert panel says safe in rinse-off products up to 0.01% (100 ppm), and in leave-on products when formulated not to sensitise.

    SourceHide
    concluded that Methylisothiazolinone is safe for use in rinse-off cosmetic products at concentrations up to 100 ppm (ie, 0.01%) and safe in leave-on cosmetic products when they are formulated to be nonsensitizing[1] US Cosmetic Ingredient Review expert panel · 2021 · open source

How much is used

  • At most 0.0015% (15 parts per million), and in rinse-off products only, in the EU.

    SourceHide
    Methylisothiazolinone ( 18 ) 2682-20-4 220-239-6 Rinse-off products 0,0015 %[3] EU law · 2026 · open source

Sources

  1. Amended Safety Assessment of Methylisothiazolinone as Used in Cosmetics International journal of toxicology, 2021US Cosmetic Ingredient Review expert panel
  2. Methylisothiazolinone Castanedo-Tardana MP et al., Dermatitis : contact, atopic, occupational, drug, 2013Review
  3. Regulation (EC) No 1223/2009 on cosmetic products, consolidated text of 18 May 2026 Publications Office of the European Union (EUR-Lex/Cellar), 2026EU law
  4. The epidemic of methylisothiazolinone contact allergy in Europe: follow-up on changing exposures Uter W et al., Journal of the European Academy of Dermatology and Venereology : JEADV, 2020Study
  5. The epidemic of contact allergy to methylisothiazolinone-An analysis of Danish consecutive patients patch tested between 2005 and 2019 Havmose M et al., Contact dermatitis, 2021Study
  6. Commission Regulation (EU) 2016/1198 amending Annex V to Regulation (EC) No 1223/2009 on cosmetic products Official Journal of the European Union, 2016EU law
  7. SCCS Opinion on Methylisothiazolinone (MI), submission III, sensitisation only (SCCS/1557/15) European Commission, Scientific Committee on Consumer Safety, 2015EU Scientific Committee on Consumer Safety
  8. Prohibited & Restricted Ingredients in Cosmetics | FDA US Food and Drug Administration

Checked against these sources on 4 November 2026. Spot a mistake? Tell us.