Methylisothiazolinone on a Label, Explained: Why the EU Banned It in Leave-On Products, What the 0.0015% Rinse-Off Limit Means, and What the US Expert Panel Said
Methylisothiazolinone is a preservative that sits in the small print of many shampoos, body washes and cleansers. It is also one of the few cosmetic ingredients that the European Union has restricted twice in two years, while the United States still lets brands decide. This guide explains what the EU rules say, what the American expert panel concluded, and how to read a label without guessing.
What methylisothiazolinone is for
Products made with water give microbes a place to grow, so most of them need a preservative. Methylisothiazolinone is one such preservative, listed in the INCI ingredient list as Methylisothiazolinone. A similar-sounding ingredient, Methylchloroisothiazolinone, is a different, related preservative and is not covered here.
The first EU change: 2016
Commission Regulation (EU) 2016/1198 amended entry 57 of Annex V of the EU Cosmetics Regulation. After that change the ingredient was allowed only in rinse-off products, at up to 0.01 percent (100 ppm). Leave-on products were no longer allowed to contain it. Only compliant products could be placed and made available on the EU market from 12 February 2017.
The reasoning came from the EU's Scientific Committee on Consumer Safety (SCCS). In an opinion adopted on 12 December 2013, it said the available clinical data indicated that 100 ppm in cosmetic products was not safe for the consumer. For leave-on products, including wet wipes, it said no safe concentration had been adequately demonstrated. The endpoint it looked at was sensitisation, meaning the immune system learning to react (contact allergy).
The second EU change: 2017
Commission Regulation (EU) 2017/1224 tightened the rinse-off limit again. The maximum in the ready-for-use preparation became 0.0015 percent (15 ppm), down from 0.01 percent. Products placed on the Union market from 27 January 2018 had to comply, and products made available from 27 April 2018. An SCCS opinion of 15 December 2015 had concluded that up to 15 ppm in rinse-off products was considered safe with respect to induction of contact allergy.
What 0.0015 percent means in practice
Fifteen parts per million is a very small share of a formula, about 1.5 mg in 100 g of product. It is a ceiling, not a typical amount. The limit applies to rinse-off products such as shampoo and body wash. Under the EU rules, a leave-on cream, serum, toner or wipe sold in the EU should not contain methylisothiazolinone at all. Brands selling in several regions sometimes use one formula for all of them, so a label is still worth reading.
What the US expert panel said
The Cosmetic Ingredient Review (CIR) Expert Panel published an amended safety assessment of methylisothiazolinone in the International Journal of Toxicology (volume 38, 2019). It concluded the ingredient is safe in rinse-off products at concentrations up to 100 ppm. It also found it safe in leave-on products when formulated to be nonsensitizing, which may be determined by a quantitative risk assessment. The panel's earlier 2010 assessment said formulations at or below 100 ppm would not be expected to pose a sensitisation risk.
Why the two answers differ
- Rinse-off limit: the EU figure is 15 ppm, the CIR panel's figure is 100 ppm
- Leave-on products: the EU does not allow it, while the CIR panel allows it if a risk assessment shows the formula is nonsensitizing
- Legal weight: an EU regulation is binding law; a CIR conclusion is an expert-panel finding, not a legal limit
US federal cosmetic law has no ingredient-by-ingredient pre-approval list, and the figure above is an expert-panel conclusion, not a federal limit. So in the US, a product can legally contain methylisothiazolinone, and the ingredient list is where you find out.
How to read a label
Look for Methylisothiazolinone in the INCI list, usually near the end because preservatives are used in small amounts. "Paraben-free" tells you nothing about this ingredient; it only says which other preservatives are absent. "Preservative-free" on a product containing water deserves a closer look at the list. For a comparison with another common preservative, see our guide to phenoxyethanol and its EU 1 percent limit. Wet wipes are covered in our makeup wipes guide.
If a product bothers your skin
Whether a particular reaction comes from this preservative, another ingredient or simple irritation cannot be decided from a label or an article. Our guide to irritant versus allergic contact dermatitis explains why those two differ, and a dermatologist can arrange proper testing. Before using a new product widely, follow our steps for how to patch test a new skincare product.
This article is general information, not medical advice. Cosmetic products do not treat or prevent disease. Patch test any new product and consult a dermatologist about skin reactions or concerns.
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