Warning: preservatives may cause allergic reactions

  • Four to five percent of the population is allergic to MIT.
  • When in doubt, read the ingredient list.


Remember this name: methylisothiazolinone. You can remember it more easily by its acronym, “MIT.” It is a preservative that is quite effective in very small doses which is why it is so widely used in cosmetics and personal care products. However, it also has the formidable effect of causing eczema, with redness and itching in 4 to 5% of the population. “It’s a fairly old product. In fact the combination of chloromethylisothiazolinone and methylisothiazolinone in a 3/1 ration is well known under the name of Kathon-CG. Chloromethylisothiazolinone and was taken off the market. Since then, methylisothiazolinone has been used less, often replaced by parabens,” explains Dr. Dominique Tennstedt, dermatologist at the Saint-Luc University Clinics in Brussels.

“This preservative is found in a countless number of products”

“However, these have recently been used less frequently because they are suspected of causing cancer. Some have been withdrawn from the market, while others have been retained. But the damage in public opinion has been done. The cosmetic industry has turned to other preservatives for use in products that contain water.

Methylisothiazolinone, which is particularly effective against bacteria and yeast, has often been chosen. It is found in a countless number of products. You are almost sure to find it in most moisturizers, shampoos and liquid soaps sold in major markets. It is also found in sunscreens and stain-removing wipes. It is found much less frequently in products sold only in pharmacies, but the only way to be certain is to read the ingredients on the product you are using. But pay attention, because since it is used in such small amounts, its name usually appears at the end of the list of ingredients.”

“This increase in its use has led to the fact that dermatologists almost every day in their offices see a patient who has developed eczema following the use of a product containing MIT. Some also develop an allergy through the use of another thiazolinone,” Dr. Dominique Tennstedt explains.

In Europe consumers are partly protected by regulations that impose a maximum content of 15 ppm for cosmetics that are designed to remain on the skin, like moisturizers. However, manufacturers can use up to 25 ppm for products that will be rinsed off, such as shampoos or shower gels. “The principle is that contact is less prolonged for these products which are quickly rinsed off. That also means, though, that allergic reactions can occur on areas of the skin that are poorly rinsed, such as the scalp, or clothing washed with detergent that are incompletely rinsed and might cause a contact reaction.”

Not having recently begun using a new product does not protect the consumer from risk: “The composition of products can change rapidly. Manufacturers are searching for alternatives to MIT, but they are rare. Its widespread use up until now has made it the second most frequent allergen (after the use of nickel in costume jewelry), to the point where the International Federation of Dermatology has called it ‘allergen of the year’. It alone is responsible for as many allergies as all perfumes combined.”

Another risk: Some products available for sale at temporary locations (street markets) or that are used by subgroups in the population are often manufactured outside the European Union. The maximum levels of MIT imposed in Europe are not necessarily respected elsewhere which might cause a more significant reaction.

What should be done if you suspect an allergy to this ingredient? “First, rinse your skin well and, if possible, certainly change products. But, if it’s a product that stays on your skin, like sunscreen, you must change products because MIT is a powerful allergen that will be impossible to avoid.”

The cosmetics industry is trying to use containers that admit less air or reduce product size by using individual doses for example. Unfortunately, the perfect preservative that doesn’t cause allergies has not been discovered. The French pharmaceutical agency doubts that one will ever be found; “by definition, all preservatives might potentially lead to safety problems.”




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