MCI/MI is a preservative system consisting of Methylchloroisothiazolinone (MCI) and Methylisothiazolinone (MI). The combination is commonly known as MCI/MI, CMIT/MIT or MCI/MI 3:1 and is used for microbial preservation of water-containing cosmetic and personal-care formulations. MCI and MI are synthetic isothiazolinone preservatives and are particularly associated with rinse-off formulations.
The commercially regulated MCI/MI mixture is based on a 3:1 ratio of Methylchloroisothiazolinone to Methylisothiazolinone. The mixture is intended to provide preservative activity against microorganisms that can affect aqueous cosmetic products. Because MCI/MI is a combination of two substances, its technical identity and quality parameters should be assessed according to the actual commercial grade supplied.
MCI/MI is not a single chemical substance with one molecular formula. It is a defined mixture containing Methylchloroisothiazolinone (MCI), CAS 26172-55-4, and Methylisothiazolinone (MI), CAS 2682-20-4. The EU cosmetic-preservative entry identifies the MCI/MI mixture under CAS 55965-84-9 and EC/List No. 611-341-5.
MCI has the molecular formula C₄H₄ClNOS, while MI has the molecular formula C₄H₅NOS. The MCI/MI system is therefore better represented as a defined preservative mixture rather than by assigning a single molecular weight or formula to the finished commercial material.
Commercial MCI/MI preparations may also contain stabilizing or carrier components depending on the grade. Historical regulatory documentation specifically describes the 3:1 mixture in association with stabilizer systems such as magnesium chloride and magnesium nitrate.
The principal function of MCI/MI is preservation. Preservatives are used in cosmetic formulations to help control microbial growth and reduce the risk of deterioration, particularly in products containing significant amounts of water. COSMILE Europe identifies both Methylchloroisothiazolinone and Methylisothiazolinone as preservatives and notes that they can occur together in rinse-off products.
MCI/MI is valued for its antimicrobial preservative functionality at very low finished-product concentrations. However, both MCI and MI have recognized skin-sensitising potential, which is an important consideration in cosmetic formulation, product development and regulatory assessment.
MCI/MI has historically been used in products such as shampoos, rinse-off hair-care products, body washes, liquid cleansing products and other aqueous rinse-off personal-care formulations where microbial preservation is required.
The regulatory position is highly important. Under the current EU Cosmetic Products Regulation Annex V, the MCI/MI mixture is listed as a preservative for rinse-off products, with a maximum concentration of 0.0015% of a mixture containing MCI and MI in the 3:1 ratio. The current ECHA regulatory database reflects Annex V as amended through April 2026.
The EU entry also states that MCI/MI and MI used alone are mutually exclusive entries; a product using the MCI/MI mixture cannot also use MI separately under the corresponding MI entry.
MCI/MI should be evaluated according to the actual active concentration, component ratio, carrier system, pH, stability and applicable finished-product regulations. The concentration of active preservative in a commercial raw-material preparation must not be confused with its permitted concentration in the finished cosmetic.
Because MCI/MI is a sensitising preservative system, formulation teams should establish the legally permitted use level for the intended market and product category. Preservative efficacy testing, compatibility assessment, packaging considerations and microbiological evaluation may also be relevant during formulation development.
For commercial procurement, the Certificate of Analysis should be used to verify the actual concentration and analytical characteristics of the supplied material rather than applying generic values from another commercial preparation.
As a MCI/MI Cosmetic Ingredient Manufacturer in India, Swapnroop can position MCI/MI for B2B requirements involving cosmetic and personal-care raw materials, subject to the actual product grade and applicable regulations. Buyers looking for an MCI/MI supplier in India should evaluate the technical identity, MCI-to-MI ratio, active concentration, physical characteristics, analytical method and batch-specific quality documentation.
For bulk cosmetic ingredient procurement, the supplied grade should be matched with the formulation's intended application and destination-market requirements. This is particularly important for MCI/MI because regulatory limits and permitted applications are significantly narrower than for many conventional cosmetic preservatives.
| Parameter | Specification |
|---|---|
| Appearance | White or colourless crystals / white powder |