Kathon CG

Kathon ® CG: the start of a long series of publications

  • De Groot AC, Liem DH, Nater JP, van Ketel WG. Patch tests with fragrance materials and preservatives. Contact Dermatitis 1985;12:87-92

In a study by the Contact Dermatoses Committee of the Dutch Society of Dermatology and Venereology from 1984, patch tests were performed with the preservative Kathon ® CG in a concentration of 1% in vaseline in 179 patients suspected of having a contact allergy to cosmetics, and there were 6 (3.4%) positive reactions. The relevance of this reaction (did the allergy play a role in the complaints for which the patient had come?) remained unknown in most patients. At that time, listing the ingredients of cosmetics was not yet mandatory, which would take until 1997. One of those 6 patients had been seen by me and I found out that this preservative was present in a commonly used cream from a well-known brand, which was also the cause of the eczema. I had since continued routine testing of Kathon CG and found another patient who had also developed allergic contact dermatitis from the use of the same cream. But I had also made someone allergic to this preservative by testing with Kathon CG 1% in petrolatum. It seemed that this was a strong allergen and so the test concentration of 1% had to be reduced. These patients were presented in De Groot AC, Liem DH, Weijland JW. Kathon CG: cosmetic allergy and patch test sensitization. Contact Dermatitis 1985;12:76-80.

Kathon was (and is) the brand name of a number of preservatives and biocides from the company Rohm and Haas in Philadelphia, United States. These all contain a mixture with the active substances methylisothiazolinone and methylchloroisothiazolinone. Kathon CG is used for application  in cosmetics, where CG stands for 'Cosmetic Grade'. It was a new and very effective preservative and was therefore widely used in cosmetic products. After this original publication, Kathon CG became my favorite subject and at least 15 more articles followed that dealt with this substance in whole or in part. It also became an important chapter in my 1988 dissertation (Chapter 4). Those articles were partly new research, but I also wrote, sometimes by invitation, review articles in Dermatosen in Beruf und Umwelt, Journal of the American Academy of Dermatology, American Journal of Contact Dermatitis and our own Contact Dermatology Newsletter.

The message from our original article on allergy to Kathon CG was immediately picked up by colleagues abroad and soon there would be articles from many European countries showing that the allergy problem was also significant in some of them. In The Lancet, Andrew Herxheimer and I described the problem in an article titled 'Isothiazolinone preservative: cause of a continuing epidemic of cosmetic dermatitis'. Don't be childish, we thought, it's an epidemic after all!

Please stop using the name Kathon CG

In 1989, the Rohm and Haas company contacted me, they wanted to come and talk to me. And so, at our home in Den Dungen, we were introduced to J.M., a six-foot-tall American, leather jacket, big rings on most of his fingers, and an avid smoker of I think Chesterfields. 'Do you allow smoking in front of your children', he asked politely. What I remember from the conversation is that he asked me not to use the name Kathon CG anymore, because it disproportionately affected his firm. That was correct, because there were several other manufacturers who marketed exactly the same preservative under a different brand name. His oral request was shortly followed by a written request, read 'demand' from a US law firm.

They were right of course, it is unwise to use brand names. What probably played a role is the rather complicated description of the preservative: 'a preservative containing as active ingredients a mixture of 5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-4-isothiazolin-3-one in an approximate ratio of 3 : 1, respectively, with MgCl2 (9%) and Mg(NO3)2 (16%) present as stabilizers'. I then (mostly) started using the names of the ingredients, but the name Kathon CG remained floating in the literature for a long time. And I had published so much about Kathon CG that at one point I used to say about it during lectures (with text slide of course): 'I have written so many articles and given so many lectures on Kathon CG that my wife suggested to change my name from Anton C de Groot into Kathon C de Groot''. Guaranteed chuckles in the room.

Practical problem: too little information

At that time, labeling of cosmetics was not mandatory, so we had a practical problem. When we found contact allergy to Kathon CG in a patient (I'll keep the name for convenience), we couldn't give her or him any information about which cosmetic products contained this agent which should therefore not be used. Of course we already knew about the very well-known cream and a few other products.

To solve that problem, in 1988 I wrote a letter to all members of the Dutch Cosmetics Association, asking them to supply a list of their products that do not contain Kathon CG. I wrote that we would include these products in a leaflet for patients allergic to Kathon CG so that they could see which products are safe. I deliberately started with a negative list. If I had asked about which products did contain Kathon CG, their cooperation would have been minimal, I guessed. The manufacturers and importers of cosmetics reacted en masse and a booklet of 12 pages was put together listing per product category which products of which brands do not contain Kathon CG.

This booklet was published by Glaxo B.V. and was distributed to all Dutch dermatologists who could give it to their Kathon CG allergic patients. By the way, I just saw in that folder that my name is not mentioned anywhere. I don't remember why…..


A little afraid

By now all cosmetics manufacturers and importers knew about my existence and research, which was always about side effects of their products, and they were, I noticed at one point, a little afraid of me. That was absolutely unnecessary, by the way. Never have I spoken negatively, either verbally or in writing, about cosmetics and their use. I had long been convinced that cosmetic products do much more good than harm. It was my concern that the products would be made as safe as possible. What probably also didn't help is that I was a staunch supporter of mandatory labeling of cosmetic products, i.e. that all ingredients must be listed on the product or a label. Actually, all manufacturers were completely against that (which I could understood well), so that I was not popular was hardly surprising.

Agression in the Jaarbeurshallen

The moment I noticed that cosmetic companies were a bit afraid of me was when my wife Janny and I visited a cosmetics convention in Utrecht. Apparently I was recognized and we could see from everything that the news of my presence spread quickly and in no time every exhibitor was aware (and on the lookout). I repeat once again that I was not an enemy of cosmetics, but I did have a bone to pick with one producer. He had stated in the questionnaire for the leaflet that his products did not contain Kathon CG. Because I suspected that I could not trust all producers on their blue eyes, I had asked my paranymph Jan-Willem Weijland from the Keuringsdienst van Waren to buy a number of products that had been reported as Kathon negative and to analyze them for the presence of the preservative. And then the main cream of that producer (which could perform all sorts of miracles, by the way) fell through the basket. That product did indeed contain Kathon CG. The analysis was repeated twice with the same result.

Okay, back to the Jaarbeurshallen. Shortly before, I had informed the manufacturer of the cream of our findings and therefore did not include its products in the negative lists for the Kathon CG brochure. When I arrived at the stand in question I found him and his wife and I introduced myself. 'Yes', his wife began, 'we know who you are and how dare you accuse us of lying? Our products do not contain Kathon CG'. It became a bit of an unpleasant conversation and the lady became louder and more agressive and did not let herself be tempered by her husband. I think we just left at one point. The neighbors had of course heard everything and the atmosphere around us was tense, so we left the fair immediately. Well, Who was right? A few months later we received a letter from the producer. He wrote that it had been found that Kathon CG was indeed present in his products. Apparently a synonym had been used, which he, who formulated all his products himself, had not recognized as Kathon CG …….

By the way, this is the only unpleasant encounter I've ever had with a cosmetics manufacturer. I have always maintained a good relationship with the Dutch Cosmetics Association, which was convinced of my good intentions. However, I have always opposed cosmetic claims that cannot be fulfilled ('anti-wrinkles'), meaningless but suggestive qualifications ('hypoallergenic'), and have always said that there should be mandatory labeling.

  • De Groot AC, Bos JD, Jagtman BA, Bruijnzeel DP, van Joost Th, Weijland JW. Contact allergy to preservatives (II). Contact Dermatitis 1986;15:218-222
  • De Groot AC, Bos JD. Preservatives in the European standard series for epicutaneous testing. Brit J Dermatol 1987;116:289-292
  • De Groot AC. Contact allergy to cosmetics: causative ingredients. Contact Dermatitis 1987;17:26-34
  • De Groot AC. Isothiazolinone preservative as important contact allergen in cosmetics. Dermatosen 1987;35:169-173
  • De Groot AC, Weijland JW. Kathon CG: A review. J Am Acad Dermatol 1988;18:350-358


This was my first major review article in an international journal. Many more would follow later, about oleamidopropyl dimethylamine (1989), methylisothiazolinone/methylchloroisothiazolinone (Kathon CG) (1990), mitomycin C (1990), methyldibromoglutaronitrile (1996), formaldehyde (2009), formaldehyde donors (2010), henna tattoos (2013), propolis (2013), octocrylene (2014), tea tree oil (2016), essential oils (2011, Dutch), allergenic ingredients in toothpastes (2017), Myroxylon pereirae resin (balsam of Peru) (2019), limonene (2019), linalool (2019), perfumes (1997, 2002, 2010 [Dutch], 2020), patch tests in drug eruptions (2022), systemic allergic/contact dermatitis (2022), Drug reaction with eosinophilia and systemic symptoms (DRESS) (2022) and Acute generalized exanthematous pustulosis (AGEP) (2022).


  • De Groot AC, Barella CGJ, Conemans JMH. Risk of sensitization to Kathon CG. Contact Dermatitis 1988;19:210-211
  • De Groot AC, Beverdam EGA, Tjong Ayong C, Coenraads PJ, Nater JP. The role of contact allergy in the spectrum of adverse effects caused by cosmetics and toiletries. Contact Dermatitis 1988;19:195-201
  • De Groot AC, Bruijnzeel DP, Bos JD, van der Meeren HLM, van Joost Th, Jagtman BA, Weijland JW. The allergens in cosmetics. Arch Dermatol 1988;124:1525-1529
  • De Groot AC, Bruijnzeel DP, Van der Schroeff JG, Bos JD. Routine testing with the preservative system Kathon CG. Int J Cosm Science 1988;10:47-51
  • De Groot AC, Bruijnzeel DP. Kathon CG: risk of sensitization. J Appl Cosmetol 1988;6:161-168
  • De Groot AC, Herxheimer A. Isothiazolinone preservative: cause of a continuing epidemic of cosmetic dermatitis. The Lancet 1989;i:314-316
  • De Groot AC. Methylisothiazolinone/methylchloroisothiazolinone (Kathon CG) allergy: an updated review. Amer J Contact Dermatitis 1990;1:151-156
  • De Groot AC. Water versus petrolatum for patch testing methylisothiazolinone + methylchloroisothiazolinone. Contact Dermatitis 1990;23:300-301
  • De Groot AC. Kontaktallergie voor een "nieuw" conserveermiddel in cosmetica: Kathon CG. Nieuwsbrief Contactdermatologie 1986;23:368-376
  • De Groot AC. Kathon CG: onderzoeksresultaten van de Commissie Contactdermatosen, en praktische informatie voor de patient. Bulletin Contactdermatosen 1989:3:77-92
  • De Groot AC, van Ulsen J, Weijland JW. Allergisch contacteczeem rond de anus met dyshidrotisch eczeem van de handen door Kathon CG in vochtige toiletdoekjes. Ned Tijdschr Geneeskd 1991;135:1048-1049
  • De Groot AC. Cosmetica die geen methyl(chloor)isothiazolinon (Kathon CG) bevatten. Ned Tijdschr Derm Venereol 1992;2:142-146                                                                                                                                                                                                                                                                                                                                                                                              

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