Isothiazolinone Allergy Found to Be Increasing in North America, Decreasing in Europe


A recent study on allergies to methylchloroisothiazolinone or methylisothiazolinone, with findings suggesting that European regulations may have diminished sensitivity rates.

Margo J. Reeder, MD

Margo J. Reeder, MD

New research indicates isothiazolinone allergy is increasing in North America but decreasing in Europe, which is believed to be due to regulation differences.

The research was conducted to compare the prevalence of allergy to methylchloroisothiazolinone/methylisothiazolinone (MCI/MI) between Europe and North America, using the prevalence of allergic contact dermatitis.

The study was led by Margo J. Reeder, MD, from the University of Wisconsin School of Medicine and Public Health’s Department of Dermatology.

“This analysis also examines trends in sensitization to the mixture MCI/MI,” Reeder and colleagues wrote. “Because testing for MI alone was only added to screening series after the prevalence of MI allergy started to increase, the trend of MI allergy can be inferred by examining the prevalence of MCI/MI sensitization over time.”


The investigators conducted a retrospective analysis using 3 databases known as the European Surveillance System on Contact Allergies (ESSCA), the North American Contact Dermatitis Group, and the Information Network of Departments of Dermatology (IVDK).

They gathered data from patients at referral patch test clinics, between 2009 and 2018, who were presenting for patch testing in the regions of both Europe and North America, assessing trends in MI contact allergy and in MCI/MI sensitization.

The researchers noted that allergy trends can be inferred by exploring the MC/MI sensitization prevalence over time, since MI testing alone was included in screening series following increases that had occurred in MI allergies.

In Europe, they noted that there were 202,166 tests for MCI/MI and 102, 667 for MI. In North America, for MCI/MI there were 23, 995 and for MI, 16, 102, with the total in both regions being 226,161 patch tests for those with MCI/MI and 118 ,779 for those with MI.


The study concluded that the prevalence rate of MI in North America increased between 2009 and 2018, but isothiazolinone allergy was found to have peaked from 2013 and 2014 before then decreasing.

Additionally, the study of European and North American patients found that those with sensitivities likely had occupational skin disease, with those at high risk being roles such as hairdressers, painters, and personal care workers.

The investigators noted that the decrease in Europe may have been due to reviews of MI contact allergies made by the European Society of Contact Dermatitis and Cosmetics Europe.

This review led to a memo that influenced the EU Scientific Committee on Consumer Safety’s recommendations against MI in certain personal care products and its move to restrict the ingredient.

The research team also noted that in the US, there are no regulations on the use of MCI/ MI or MI in personal care products.

“The results of this cohort study suggest that although contact allergy to isothiazolinones has decreased in Europe, it continues to increase in North America,” they wrote. “Earlier and more stringent regulation of MI in Europe is associated with these divergent trends.”

The study, “Trends in the Prevalence of Methylchloroisothiazolinone/Methylisothiazolinone Contact Allergy in North America and Europe,” was published online in JAMA Dermatology.

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