Methylchloroisothiazolinone and Methylisothiazolinone

What Is It?
Why Is It Used?

Methylisothiazolinone (MI) and Methylchloroisothiazolinone (MCI) are preservatives.  Preservatives are natural or man-made ingredients designed to help ensure the safety and quality of products by protecting them against the growth of microorganisms during storage and, most importantly, during use by consumers.  Any product that contains water is particularly susceptible to being spoiled by microbial growth, causing problems such as discoloration, unpleasant odors or breakdown. Under certain conditions, microorganisms can even grow to potentially harmful levels. Preservatives are designed to help prevent these problems.

Although Methylisothiazolinone (MI) may be used in cosmetics and personal care products alone, it is often used as a mixture with Methylchloroisothiazolinone [(MCI). In cosmetics and personal care products historically, Methylisothiazolinone, or the mixture, Methylisothiazolinone and Methylchloroisothiazolinone, was used in various rinse-off and leave-on formulations including hair products, shampoos, skin care products, bath products, eye and facial makeup, wet wipes and suntan products.  More recently, due to concerns being raised about potentially increasing rates of skin sensitivity to MI, some cosmetic and personal care product manufacturers have begun removing it from leave-on products such as lotions and wipes (see more under ‘SAFETY’ tab).

Follow this link for more information about how preservatives protect cosmetics and personal care products.

Cosmetic products can become contaminated through consumer use.   The product itself may come into contact with the skin potentially exposing the product to bacteria and fungi naturally found on our skin. Consumers may also use and store cosmetic products, like shower gels, in warm and moist conditions, ideal for microbial growth.  As such, the inclusion of ingredients which are capable of preventing or inhibit microbial growth is critical to assuring the quality and safety of cosmetic products.

Safety Information


The Food and Drug Administration (FDA) permits the use of Methylisothiazolinone (2-methyl-4-isothiazoline-3-one) and Methylchloroisothiazolinone (5-Chloro-2-methyl-4-isothiazolin-3-one) as indirect food additives, as antimicrobial agents, as components of adhesives and as components of coatings.


The safety of Methylisothiazolinone and Methylchloroisothiazolinone have been assessed several times by the Cosmetic Ingredient Review (CIR) Expert Panel. The CIR Expert Panel, ( is an independent, non-profit scientific body. Established in 1976, the Personal Care Products Council (the Council) initiated the CIR program at the suggestion and with the support of the Food and Drug Administration (FDA) and the Consumer Federation of America (CFA).  CIR assesses the safety of ingredients used in cosmetic and personal care products in the U.S.  The CIR Expert Panel consists of world-renowned scientists and physicians who have been publicly nominated by consumer, scientific and medical groups, government agencies, and industry. The CIR and its review process are independent from the Council and the cosmetics industry, although the program is funded by industry to support the administrative staff.  Members of the Panel must meet the same conflict of interest requirements regarding financial interests as special non-government advisory experts to FDA.

In 2010, the CIR Expert Panel assessed the safety of Methylisothiazolinone when used alone and concluded that it was safe for use as a cosmetic ingredient at concentrations up to 100 ppm.In 2013, the CIR Expert Panel reopened the safety assessment of methylisothiazolinone (MI) to gather and evaluate newly provided clinical data indicating a higher than expected frequency of individuals who have allergic reactions to MI when used alone.  The Panel noted the numerous reports of contact allergy to MI in Europe and the increased incidences of contact allergy to MI observed in their own clinical experience.

The CIR also noted that the European Union’s Scientific Committee on Consumer Safety (SCCS) had recently updated its opinion on the use of MI and had found that in leave-on cosmetic products (including “wet wipes”) no safe concentration had been adequately demonstrated for preventing allergic skin reactions.  In rinse-off cosmetic products, the SCCS had concluded that concentrations up to 0.0015% (15 ppm) MI are safe.

Based on the results of detailed scientific skin allergy risk assessments and human clinical tests, the CIR Expert Panel reaffirmed their 2010 conclusion that it was safe to use MI in rinse-off product categories at concentrations up to 100 ppm.  However, they concluded that MI use in many leave-on product categories would be safe only at concentrations lower than 100 ppm and only when it could be demonstrated that the concentration used does not cause allergic skin reactions.

These recommendations for MI in rinse-off and leave-on cosmetic products were intended to prevent new cases of allergic skin reactions to MI. The CIR Expert Panel cautioned, however, that individuals who know that they are allergic to MI should avoid personal care products that contain MI.

European Union (EU)

The mixture of Methylchloroisothiazolinone and Methylisothiazolinone is also listed in the European Cosmetics Regulation and is authorized for use at a maximum concentration of 0.0015% (15 ppm).

The Scientific Committee for Cosmetic Products and Non-food products intended for Consumers (SCCNFP; now called the Scientific Committee on Consumer Safety, the SCCS, and is the European Commission’s independent committee of scientists which assesses ingredient safety) conducted a safety review of methylisothiazolinone when used alone and published their opinion in 2004.  Following this, MI was authorized as a preservative for use in leave-on and rinse-off cosmetic products up to a maximum concentration of 0.01% (100ppm).

In more recent years, publications from the dermatology community reported clinical evidence of an increase in positive skin allergy test reactions to MI in patients suffering from dermatitis through cosmetic use, especially in Europe. After reviewing all available new data, in 2013, the SCCS updated its opinion on the use of MI and concluded that in leave-on cosmetic products (including “wet wipes”) no safe concentration had been adequately demonstrated.  In rinse-off cosmetic products, the SCCS had concluded that concentrations up to 0.0015% (15 ppm) MI are safe.

The European cosmetics trade association, Cosmetics Europe, with the support of experts from the dermatological community, ingredient suppliers and cosmetic product manufacturers conducted their own review of the clinical, toxicological and post-market safety surveillance data for MI. They also conducted a quantitative sensitization risk assessment that supports safe use of MI in rinse-off products and leave-on hair products.  In December 2013, the European Cosmetics industry voluntarily agreed to the removal of MI from leave-on skin products, including cosmetic wet wipes. This is expected to significantly decrease the incidence of new cases of skin allergy to MI.

SCCNFP Opinion on Methylisothiazolinone, 23 April 2004:

SCCS Opinion on Methylisothiazolinone, Submission II (Sensitization Only), 12 Dec 2013:…

Cosmetic Europe’s Voluntary Decision to Stop Using MI in Leave-On Cosmetic Products:…


Health Canada permits the use of Methylisothiazolinone/Methylchloroisothiazolinone, in combination, at concentrations equal to or less than 0.0015% (15 ppm) in rinse-off products and 0.00075% (7.5 ppm) in leave-on products. When used alone, Methylisothiazolinone may be used at concentrations up to 0.01% (100 ppm).

Detailed assessments of available safety data for Methylisothiazolinone, both alone and when in combination with Methylchloroisothiazolinone, can be found in the following U.S. Cosmetic Ingredient Review Expert Panel reports:

  1. Final Report on the Safety Assessment of Methylisothiazolinone.  IJT 29(Suppl. 3) :187-213,2010:
  2. Amended Safety Assessment of Methylisothiazolinone as Used in Cosmetics.  Sept. 9, 2014:…


The European Commission’s Scientific Committee on Consumer Products (SCCP) Clarification of the SCCNFP Opinion on the Update of Entry No. 39 of Annex VI to Directive 76/768/EEC on Cosmetic Products: Mixture of 5-Chloro-2-Methyl-Isothiazolin-3(2H)-one and 2-Methylisothiazolin-3(2H)-one

The European Commission database with information on cosmetic ingredients

Search the FDA Code of Federal Regulations