Methylisothiazolinone (MIT) is a preservative used to protect liquids against bacteria and mould. It is found in many consumer products such as shampoos, household cleaners and wall paints. The disadvantage is that it can trigger contact allergies. This can lead to skin redness, blisters and itching, and sometimes even severe eczema. Over the last several years, the number of people allergic to MIT has increased, which is why the use of the preservative is now restricted by law. Cosmetics that stay on the skin may not contain the substance. Body care products that are rinsed off may only contain 15 ppm (milligrams per litre).
While the effect of MIT in cosmetics has been well researched, the allergy risk from textiles washed with laundry detergents containing MIT was previously unclear. In search of the answer, Dr Maja Hofmann, a dermatologist at Charité – Universitätsmedizin Berlin, and an international research group have now ‘put it through the wash’. (1) The team washed three textile samples in cotton, polyester and cotton/polyester blend together with normal laundry in a household washing machine. The washload was laundered with 75ml of a universal detergent to which varying concentrations the preservative MIT were added (1000 ppm, 100 ppm and 0 ppm). The laundry was then line dried. In another series of tests, the researchers repeated the wash cycle ten times in order to determine whether the preservative accumulates with repeated washing. They then examined the dry textiles using high-performance liquid chromatography. The result: there were no detectable amounts of MIT in either the samples that were only washed once or the ones that were washed ten times (the detection limit was 0.05 ppm). Even the more common detergents containing very high levels of MIT (1000 ppm) did not leave behind any residues of the preservative in the textiles.
The European Centre for Allergy Research Foundation (ECARF) also ordered an additional test at ALAB (analysis laboratory in Berlin) in order to determine whether MIT is still present in freshly washed, damp laundry. The result was clear: there were no detectable amounts of MIT. It is therefore safe for people who are allergic to MIT to remove the laundry from the washing machine and hang it up to dry. (2)
According to Dr Torsten Zuberbier, co-author of Dr Maja Hofmann’s study and spokesperson for Allergie-Centrum-Charité, the results give people who are allergic to MIT reassurance as they go about their daily lives. This is also good news for those who often sleep away from home: “People with MIT allergies can lie in their hotel beds or spend the night at friends’ homes without worry. Even if detergents containing MIT have been used, the preservative is no longer present in the laundered items.”