Methylisothiazolinone
Methylisothiazolinone (MI) is a preservative used in rinse-off cosmetics and wet wipes. A sharp rise in contact allergy led the EU to ban it from leave-on products, and it remains a significant sensitiser — so it is flagged for sensitive and eczema-prone skin.
Methylisothiazolinone protects water-based products from bacteria. Its increased use around 2010–2013 was followed by an epidemic of allergic contact dermatitis, making it a dermatology "allergen of concern."
Since 2017 EU rules prohibit MI in leave-on products (such as creams and lotions) and cap it in rinse-off products at 15 ppm. People with a known MI allergy, sensitive skin, or eczema should check for it — especially in wet wipes and shampoos.
Who this affects
Caution
- Sensitive skin & eczema: A potent preservative contact allergen; EU-banned in leave-on products and best avoided on reactive skin.
Frequently asked questions
Its safety depends entirely on how it is used. EU regulators concluded no safe concentration could be demonstrated for leave-on products, so MI is banned in those, while a low level of 0.0015% (15 ppm) is permitted in rinse-off products. This is an informational summary, not medical advice — if you react to a product, check the ingredient list and see a dermatologist.
Following its widespread use, MI caused what dermatologists described as an epidemic of allergic contact dermatitis, and the SCCS could not demonstrate any safe concentration for leave-on products including wet wipes. Commission Regulation (EU) 2016/1198 therefore prohibited MI in leave-on cosmetics, applicable from 12 February 2017.
Yes — MI is a well-documented contact allergen and was named Contact Allergen of the Year 2013 by the American Contact Dermatitis Society, linked to a sharp rise (an "epidemic") in allergic contact dermatitis. Reactions can range from localised scalp or hand dermatitis to widespread, and even airborne, dermatitis in highly sensitised people. Allergy is confirmed by patch testing, which is the authoritative way to know if MI affects you.
In the EU, MI is only permitted in rinse-off products such as shampoos, shower gels and cleansers, at a maximum of 0.0015% (15 ppm). It is not allowed in any leave-on product like creams, lotions or wet wipes. When present, the label must list "Methylisothiazolinone" among the ingredients.
If you have known MI allergy, avoiding all MI-containing products is the standard advice, since even the low rinse-off levels can trigger reactions in sensitised people. For sensitive or eczema-prone skin without a confirmed allergy, many people avoid it as a precaution, but patch testing by a dermatologist is the authoritative way to confirm sensitivity. Managing contact dermatitis centres on identifying and avoiding the trigger.