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Methylchloroisothiazolinone

A strong preservative, always paired.

What it does

Stops bacteria and fungi from growing. It's only used mixed with methylisothiazolinone (MI).

Good to know

A common cause of skin allergy, especially in leave-on products. That's why the EU, UK, Canada and Australia allow the mix only in rinse-off products, up to 0.0015%.

Often found in: Shampoos, Anti-dandruff shampoos, Shower gels, Liquid soaps

Around the world

• United States: No FDA limit. The FDA doesn't approve cosmetic ingredients before sale. Source
• EU and UK: Only mixed with MI (3:1), in rinse-off products, max 0.0015%. Not allowed in leave-on products. Source
• Canada: Only with MI, in rinse-off products, max 0.0015% in total. Not allowed in leave-on products. Source
• Australia: Allowed in rinse-off cosmetics up to 0.0015% (with MI). Otherwise it's controlled (Schedule 6). Source

Sources

• Recent increase in allergic reactions to MCI/MI: is MI the culprit? (Contact Dermatitis, 2012) (Medical)
• Methylisothiazolinone: 2013 Allergen of the Year (Dermatitis, 2013) (Medical)