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Methylsothiazolinone (MI) and methylchloroisothiazolinone (MCI) are two preservatives used in haircare products.

Preservatives help keep people safe by preventing the growth of bacteria and mold in products while they’re used at home.

Substances like MI and MCI are used in many haircare products, because they protect them from spoiling. However, some people with unique skin sensitivities should not use these products, because they can trigger an allergic skin reaction. Let’s look at these ingredients a little more closely.

How MI and MCI work

Both MI and MCI are incredibly effective preservatives commonly used in beauty care products. They have several useful properties:

  • Methylisothiazolinone is a biocide and is used to control microbial growth in water containing solutions

  • Methylchloroisothiazolinone has antibacterial and antifungal properties, giving it broadly the same uses as MI

  • Together, these two substances make preserving cosmetics far more efficient and effective.

MI, MCI and your health

MI and MCI are some of the most thoroughly tested preservatives worldwide, and have safe ranges established by regulatory agencies, such as the European Union.

MI and MCI should only be used in products that are rinsed off after use, like shampoos and conditioners. That’s because leaving them on your skin can increase the chance of developing an allergic reaction if you are naturally sensitive to them.

Used in the proper amounts in rinse-off products like shampoo and conditioner, they are safe and effective, and they help protect you by keeping your shampoo and conditioner free from microbial contamination.

For this reason, Head & Shoulders only uses MI and MCI in our rinse-off shampoos and conditioners where they are safe to use.

However, if you have been diagnosed with an allergy to MI or MCI, you should avoid using products with these ingredients.

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