Shampoo Allergy: Top Allergens

# 3 MCI/MI

Methylchloroisothiazolinone (MCI) and methylisothiazolinone (MI) are two separate ingredients but frequently used together at a ratio of 3 parts MCI to 1 part MI in preservatives. MCI/MI is commonly used in cosmetic and industrial applications.

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Interestingly, MCI and MI were initially introduced in the 1980s in various occupational applications – in glues, paints, and cleaners as a mixture.  Since 2005, it has been more widely used in cosmetics, sunscreens and household products, such as moist wipes, shampoos and conditioners.  It’s also found in cleaners and liquid laundry products and household cleaners.

The world is likely become more sensitized and allergic to MCI/MI. Some reports have shown an increase in sensitization to MCI/MI and MI by itself.The global frequency of sensitization to MCI/MI remained constant at around 2.1% from 1998-2009, but increased to 3.9% in 2011. In shampoos, it represents the third most common allergen after fragrance and cocamidopropyl betaine. 51.4 % of shampoos contain MCI/MI.

Many countries have changed their regulations on how MCI/MI can be used. Interested individuals should contact local authorities as regulations differ from country to country.

The general trend is a recommendation to ban MCI/MI in leave on products and allow it in rinse off products at tightly regulated concentration levels. In Canada, an alert was issued stating that “after June 14, 2016, all products intended for use by children under the age of three that contain MI/MCI should no longer be available for purchase. All other leave-on products containing MI/MCI were longer available for purchase after December 31, 2016.

In Canada, MI is allowed as a preservative at a maximum concentration of 0.01 %. MCI is no longer permitted in leave on products but is accepted in rinse off products at a maximum concentration of 15 ppm (0.0015%) This 15 ppm is the typical threshold in most countries.


Increasing trend of sensitization to Methylchloroisothiazolinone/methylisothiazolinone (MCI/MI). 


1. Scherrer et al. An Bras Dermatol. 2014 May-Jun; 89(3): 527. 

2.  Geier J, Lessmann H, Schnuch A, Uter W. Recent increase in allergic reactions to methylchloroisothiazolinone/methylisothiazolinone: is methylisothiazolinone the culprit? Contact Dermatitis. 2012;67:334–341.  

3.  Mowad CM. Methylchloroisothiazolinone revisited. Am J Contact Dermat. 2000;11:115–118.  3. Lundov MD, Thyssen JP, Zachariae C, Johansen JD. Prevalence and cause of methylisothiazolinone contact allergy. Contact Dermatitis. 2010;63:164–167.  

4. Urwin R, Wilkinson M. Methylchloroisothiazolinone and methylisothiazolinone contact allergy: a new epidemic. Contact Dermatitis. 2013;68:253–255. 

Dr. Jeff Donovan is a Canadian and US board certified dermatologist specializing exclusively in hair loss. To schedule a consultation, please call the Whistler office at 604.283.1887

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