The prevalence of contact allergy triggered by a common product preservative, isothiazolinone, has decreased in Europe while it has increased in North America. The trends are likely driven by regulatory differences, a retrospective cohort study suggests.

“Between 2009 to 2018, the global burden of isothiazolinone allergy showed divergent trends between North American and European countries,” lead study author Margo J. Reeder, MD, of the University of Wisconsin School of Medicine and Public Health in Madison, and her colleagues write. The study was published online January 18 in JAMA Dermatology.

Isothiazolinone contact allergy peaked in Europe in 2013–2014 before gradually decreasing, they found. The prevalence of isothiazolinone allergy steadily increased in North America during the study period. “Earlier and more stringent regulation of MI [methylisothiazolinone] in Europe is associated with these divergent trends,” they write.

Common Ingredients Worldwide

Isothiazolinone preservatives, which are added to personal and industrial products, cause allergic contact dermatitis worldwide, the authors write. The preservatives are found in a wide range of leave-on and rinse-off water-based personal care products, such as shampoo and other hair products, dishwashing liquid, face cream, body lotion, shower gel, liquid soap, and wet wipes, as well as in water-based paint.

A mixture of methylchloroisothiazolinone (MCI) and MI has been used to prevent microbial growth in products since the 1980s. In 2005, US and European regulators approved MI alone at higher concentrations as a preservative in personal care products. Coupled with consumer concerns about other preservatives, such as parabens (a rare allergen), use of MI in personal care products increased, the authors write.

Subsequently, researchers reported a global increase in the prevalence of contact allergy to isothiazolinones, the authors write. Regulatory restrictions on MI in personal care products were implemented in 2013 in Europe and in 2015 in Canada but not in the US.

Patch Test Data Reveal Latest Trends

To compare prevalence trends of allergic contact allergy to MI and sensitization to the MCI/MI mixture in North America and in Europe, Reeder and her colleagues compared the prevalence of positive patch test reactions to MCI/MI and to MI alone in North America and in Europe between 2009 and 2018.

They analyzed data from the North American Contact Dermatitis Group (NACDG), the European Surveillance System on Contact Allergies (ESSCA), and the Information Network of Departments of Dermatology (IVDK) in 2-year intervals. The data came from patients who had been patch tested at referral patch test clinics in North America and Europe.

Over the decade, the study sites conducted patch testing for 226,161 patients for MCI/MI and 118,779 for MI. Most data came from Europe. The researchers found the following:

• In Europe, isothiazolinone allergy peaked in 2013 and 2014; MCI/MI positivity reached 7.6% (ESSCA) and 5.4% (IVDK) before decreasing to 4.4% (ESSCA) and 3.2% (IVDK) in 2017–2018.

• In North America, MCI/MI positivity rose steadily from 2.5% in 2009–2010 to 10.8% in 2017–2018.

• In Europe, there were 5.5% (ESSCA) and 3.4% (IVDK) positive reactions to MI, compared with 15% (NACDG) in North America in 2017–2018.

Divergent Contact Allergy Trends Linked to Regulatory Approaches

The downward trend of isothiazolinone allergy in Europe after its peak in 2013 and 2014 may have been due in part, the authors explain, to a memo released in 2013 by Cosmetics Europe after it and the European Society of Contact Dermatitis reviewed reports of increased contact allergy to MI. The memo urged companies to remove MI from leave-on products.

Later that year, the European Union’s Scientific Committee on Consumer Safety advised omitting MI from leave-on consumer personal care products and moved to restrict the ingredient in rinse-off products to less than 15 ppm. The recommendation took effect in 2015.

That year, Canada banned the use of MCI/MI in leave-on products but allowed MI alone in leave-on products until 2018. The total concentration of MI and MCI in wash-off products was limited to less than 15 ppm.

The authors add that, to their knowledge, the US government does not restrict the use of MCI/MI or MI.

Policy Implications for Contact Allergy

MI is still widely used in “countless products,” including shampoos, skin cleansers, dishwashing and laundry detergents, paints, and adhesives, Daniel W. Shaw, MD, associate professor of dermatology at the University of California, San Diego, told Medscape Medical News by email.

Dr Daniel Shaw

“Exact figures between the US and Europe are difficult to compare due to differing patch test concentrations, but the overall trends strongly suggest that stricter and earlier regulation in Europe resulted in lower MI allergy prevalence there than in the US,” added Shaw, who was not involved in the study.

Steven R. Feldman, MD, PhD, professor of dermatology at Wake Forest University School of Medicine in Winston-Salem, North Carolina, said by email that accurate information on allergic reaction prevalence is difficult to find.

Dr Steven Feldman

“The NACDG, ESSCA, and IVDK databases may contain the best data available, but the data depend on people who get patch tested and are not directly informative of the allergy rates in the general population,” added Feldman, who was not involved in the study.

“The great majority of people in the population may not be allergic,” he said. “For those with itchy rashes, getting patch tested or avoiding products with preservatives may be prudent. Broad regulations, however, should consider the overall risks and benefits in the population, and this particular study does not fully capture those issues.”

Dr Kelly Tyler

“This study shows that government regulations are important to limit consumer exposure to common allergens, especially to the concentrations used in personal care products,” Kelly Tyler, MD, associate professor of dermatology at the Ohio State University Wexner Medical Center in Columbus, Ohio, noted by email. She was not involved in the study.

She advised clinicians to ask their patients who may have allergic contact dermatitis whether they have been exposed to products containing these compounds.

“All personal care products in the store contain preservatives, and their maximum concentrations should be limited,” she advised. “The Expert Panel for Cosmetic Ingredient Safety should establish stricter guidelines for MI use in personal care products, especially given the findings of this study.”

Has MI Contact Allergy in North America Peaked?

“In the US, MI has not been banned from leave-on skin-care products, but recently, its use has markedly decreased,” Shaw commented. “Hopefully, the prevalence of MI contact allergy will also begin to decrease.”

New evidence is promising. In a related study published online January 19 in Dermatology, Joel G. DeKoven, MD, MHSc, FRCPC, of the University of Toronto, Ontario, Canada, and his colleagues reported the NACDG 2019–2020 patch test results for MI in North America. They found that 13.8% of patients tested positive for MI.

“For the first time, MI positivity did not increase between reporting periods,” they conclude. “The epidemic of MI contact allergy in North America may have reached a plateau.”

Information regarding funding for the study was not provided. Reeder has financial relationships with the American Contact Dermatitis Society and a publishing company. Several co-authors have financial relationships with the pharmaceutical industry. Tyler, Shaw, and Feldman report no relevant financial relationship.

JAMA Dermatol. Published online January 18, 2023. Full text

Dermatology. Published online January 19. Abstract

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