LC–MS/MS Detects MCI/MI in Danish Soaps and Shampoos

Allergic reactions to the common preservatives methylchloroisothiazolinone (MCI) and methylisothiazolinone (MI) are still widespread across the European Union (EU), even though regulations are in place to limit their use. To get a clearer picture of how often these ingredients show up in cosmetic products sold in Denmark, researchers set out to identify which types of products contain them and check whether rinse-off products (like shampoos and soaps) were staying within the legal limit of 15 ppm. To do this, they tested 30 products (16 shampoos and 14 liquid soaps) using liquid chromatography-tandem mass spectrometry (LC–MS/MS). A paper based on this research was published in the journal Contact Dermatis.¹

What Are MCI and MI, and Why Have They Become Controversial Ingredients in Cosmetic Products?

Preservatives are added to water-based products to stop them from going bad due to bacterial or fungal growth. Isothiazolinones are a group of preservatives that do this job very well, but they come with a drawback: they can trigger skin allergies. The combination of methylchloroisothiazolinone (MCI) and methylisothiazolinone (MI), mixed in a 3:1 ratio, has been widely used since the 1980s to preserve everything from cosmetics and household cleaners to industrial products.² The widespread use of MCI/MI triggered a wave of allergic skin reactions across Europe, which led regulators to step in. By 1989, the allowed concentration of this preservative blend in cosmetic products was capped at 15 parts per million (ppm).³ Around the turn of the millennium, when the patent on the MCI/MI blend (sold under the brand name Kathon) ran out, the industry began exploring the idea of using MI on its own as a preservative. After safety assessments were carried out before it went to market, MI was approved for use as a standalone preservative in cosmetic products across the EU, with a maximum allowed concentration of 100 ppm.⁴ This was quickly followed by a surge in newly diagnosed skin allergies linked to MI, particularly tied to cosmetic products, wet wipes, and water-based paints.^5,6 In the years that followed, growing awareness among regulators and other key players, backed by data coming in from dermatology departments across Europe, put increasing pressure on authorities to act. As a result, following a formal opinion from the EU's Scientific Committee on Consumer Safety in 2013, both MCI/MI and MI were banned from cosmetic products that stay on the skin, such as lotions and creams.⁷

How Commonly Are MCI and MI Used in Cosmetic Products on the Danish Market, and Are Manufacturers Staying within Legal Limits?

The researchers tracked down products containing MCI/MI or MI using Kemiluppen, a Danish database of cosmetics on the market. In total, they identified 257 products containing these preservatives, mostly shampoos (127), conditioners (98), and liquid soaps (8). For the laboratory testing, they picked 30 products (16 shampoos and 14 liquid soaps) 25 of which were labeled as containing MCI/MI or MI, and 5 that were not. The results raised some concerns. Two of the 25 labeled products (8%) contained more than the legal limit of 15 ppm, and 4 products didn't meet the required ratio of MCI to MI (which should be 3:1). This ratio matters because MCI is considered more irritating than MI, so the balance between the two is regulated for safety reasons.¹

“MCI/MI, report the authors of the paper,¹ “is used infrequently in cosmetic products. All except two products complied with the limit in the regulation. Given the continued occurrence of contact allergy, this indicates that the limit (15 ppm) may be too high to be sufficiently protective.”

The study has a few limitations to keep in mind. The fact that the product data came from Kemiluppen means the findings may reflect what shoppers tend to buy rather than a truly random snapshot of the market. Only 30 products were chemically tested, which is a small slice of an enormous and constantly changing market. Since only labeled products were tested, any mislabeled or unlisted products containing MCI/MI or MI would have been missed entirely. That said, because Denmark follows EU-wide regulations and many products are sold across the region, any compliance issues found here likely reflect a broader European problem rather than one unique to Denmark.¹

Read More on Similar Topics
Researchers Use GC-MS to Explore Patchouli Oil for Hair Care

References

1. Pedersen, M. K.; Schwensen, J. F. B.; Alfonso, J. H. et al. Methylchloroisothiazolinone and Methylisothiazolinone 10 Years After Regulation: A Case Story of Liquid Soaps and Shampoos. Contact Dermatitis 2026. DOI: 10.1111/cod.70202
2. Lundov, M. D.; Moesby, L.; Zachariae, C. et al. Contamination Versus Preservation of Cosmetics: A Review on Legislation, Usage, Infections, and Contact Allergy. Contact Dermatitis 2009, 60 (2), 70-78. DOI: 10.1111/j.1600-0536.2008.01501.x
3. European Union, Eleventh Commission Directive 89/174/EEC of 21 February 1989 Adapting to Technical Progress Annexes II, III, IV, V, VI and VII to Council Directive 76/768/EEC on the Approximation of the Laws of the Member States Relating to Cosmetic Products.https://eur-lex.europa.eu/eli/dir/1989/174/oj/eng (accessed 2026-01-07)
4. European Union, The Commission of the European Communities. Commission Directive 2005/42/EC of 20 June 2005 Amending Council Directive 76/768/EEC, Concerning Cosmetic Products, for the Purposes of Adapting Annexes II, IV and VI Thereto to Technical Progress. https://eur-lex.europa.eu/eli/dir/2005/42/oj/eng (accessed 2025-11-05)
5. Schwensen, J. F.; Uter, W.; Bruze, M. et al. The Epidemic of Methylisothiazolinone: A European Prospective Study. Contact Dermatitis 2017, 76 (5), 272-279. DOI: 10.1111/cod.12733
6. Flury, U.; Palmer, A.; Nixon, R. The Methylisothiazolinone Contact Allergy Epidemic in Australia. Contact Dermatitis 2018, 79 (3),189-191. DOI: 10.1111/cod.13025
7. Lidén, C.; White, I. R. Increasing Non-Cosmetic Exposure and Sensitization to Isothiazolinones Require Action for Prevention: Review. Contact Dermatitis 2024, 90 (5), 445-457. DOI: 10.1111/cod.14523