Methylisothiazolinone (MI) in shampoo, wipes and cleaners: the allergy epidemic explained

This is the third in our series on common ingredients worth knowing about, after triethanolamine and diethanolamine. Methylisothiazolinone, usually shortened to MI or MIT, is different from those 2: the concern isn't a theoretical cancer risk from animal studies, it's a very well documented allergy that became so common in Europe that regulators banned it from leave-on products. It's a preservative, and it's probably in something in your bathroom or under your sink right now.

What is methylisothiazolinone?

MI is a synthetic preservative. Its job is to stop bacteria and mould growing in water-based products, which is a real need: an unpreserved shampoo goes off. It's cheap, works at tiny concentrations and, unlike parabens, nobody had heard of it, which made it attractive when brands started advertising "paraben-free" in the 2000s. It had been used since the 1980s in a mixture with its chlorinated cousin methylchloroisothiazolinone (MCI), and was allowed on its own in cosmetics from 2005, at up to 100 parts per million.

What followed, in the words of the dermatologists who tracked it, was an epidemic of contact allergy.

Where you'll find it

Shampoos and conditioners, body wash, liquid hand soap, wet wipes (baby wipes especially, until the backlash), sunscreens, moisturisers and make-up in markets that still allow it, and a long list of household products: dishwashing liquid, laundry detergent and fabric softener, surface cleaners, and water-based paint. The paint matters: people have developed rashes and breathing symptoms from freshly painted rooms, and painters are a recognised occupational risk group.

How to spot it on a label

Cosmetics have to list it under its INCI name. Look for:

• Methylisothiazolinone (MI, MIT)
• Methylchloroisothiazolinone (MCI), usually listed together with MI as the mixture
• Benzisothiazolinone (BIT) and octylisothiazolinone (OIT), related preservatives more common in household products and paint
• Trade names you may see on industrial or cleaning products: Kathon, Neolone

Household cleaning products in South Africa aren't required to list full ingredients the way cosmetics are, so a cleaner can contain it without saying so. "Contains methylisothiazolinone, may produce an allergic reaction" is a warning you'll sometimes see on imported products; that wording is an EU requirement.

Is methylisothiazolinone safe? What the research actually says

It is a strong skin sensitiser. That's the finding, and it's not disputed. In 2011 a Danish review found 1.5% of patients patch-tested in dermatology clinics were already allergic to MI, only 6 years after it was allowed on its own, and warned that this could be the start of an epidemic. They were right: by 2013 to 2015, clinics across Europe were reporting MI allergy in 5% to 10% of patients tested, and in some the rate was higher. The American Contact Dermatitis Society named it Contact Allergen of the Year for 2013.

What the allergy looks like. Allergic contact dermatitis: red, itchy, scaly or blistered skin where the product touched you. Classic patterns are eczema on the hands from liquid soap and wet wipes, on the face and eyelids from shampoo running down and from wipes, on the scalp and hairline, and in the nappy area of babies from wipes. Once you're sensitised, it's permanent, and reactions can be severe: some people react to a product at concentrations well below the legal limit.

Airborne reactions. MI evaporates from wet paint and from drying laundry, and dermatologists have documented facial dermatitis in sensitised people simply from being in a freshly painted room. This is unusual for a cosmetic preservative and is part of why regulators moved.

What it isn't. There's no credible evidence that MI causes cancer, affects hormones or harms you at the trace levels in a rinsed-off product if you're not allergic to it. Some animal and cell studies have looked at nerve-cell toxicity at high doses; that's not relevant to skin exposure from a shampoo. The problem with MI is specific and real: it makes a surprising number of people allergic, and once that's happened, it's very hard to avoid.

What the rules are

European Union. Banned in leave-on cosmetics (moisturisers, sunscreen, make-up, wipes) since February 2017. In rinse-off products (shampoo, body wash, hand soap), the limit was cut from 100 ppm to 15 ppm from 2018, after the EU's scientific committee concluded 15 ppm was the level at which it stopped inducing new allergies.

United States. Still permitted in leave-on and rinse-off products. The industry's own safety panel recommends a limit, but it's voluntary.

South Africa. Cosmetics regulation here follows the EU list through the SABS standard and the Foodstuffs, Cosmetics and Disinfectants Act, but enforcement is light and imported products from non-EU markets are common. In practice, check the label; you can't assume the EU limit applies.

Household products and paint. Not covered by cosmetics rules anywhere. The EU requires an allergy warning on the label above a threshold; most other markets don't.

So should you avoid it?

If you've never had a reaction, a rinse-off product within the EU limit is low risk. The practical reasons to avoid it anyway:

1. Sensitisation is permanent. Unlike an irritant, which stops bothering you when you stop using it, an allergy stays. The best way not to become allergic is not to be exposed, and MI sensitises more people than almost any other preservative in use.
2. Leave-on exposure is the risk, and it still happens: wipes, moisturisers and sunscreens from non-EU markets, and household products you don't rinse off your hands.
3. Babies and people with eczema have more permeable skin and are the groups dermatologists see most. If that's your household, it's the first preservative to cut.
4. If you have unexplained hand, face or eyelid eczema, ask your dermatologist for a patch test that includes MI at 2,000 ppm (the current recommended test concentration). It's one of the most common positive results, and it's missed if the test isn't done.

Where to look first: liquid hand soap, wipes, and whatever you wash with daily. Then the laundry and cleaning cupboard.

Frequently asked questions

Is MI the same as parabens?
No. Parabens are a different preservative family with a different (and weaker) safety concern. MI was widely adopted as a paraben replacement, and caused far more skin allergy than parabens ever did. "Paraben-free" tells you nothing about MI.

Is it in baby wipes?
It was, widely, until around 2014, when several big brands removed it after a wave of nappy-area and facial dermatitis reports. Many have switched; some imported brands haven't. Check the pack.

I've used MI products for years with no problem. Am I safe?
Probably, for now. Sensitisation can happen at any point after repeated exposure, and it's more likely with leave-on use and on damaged skin. Not having reacted yet isn't immunity.

What should a product use instead?
True soap needs nothing. For water-based products, the options with the best safety records are the organic acids (sodium benzoate, potassium sorbate) at a low pH, and phenoxyethanol at the regulated 1% limit. None is perfect; all sensitise far fewer people than MI.

The sources

• Lundov MD, Krongaard T, Menné TL, Johansen JD (2011). Methylisothiazolinone contact allergy: a review. British Journal of Dermatology 165:1178–1182. View →
• Castanedo-Tardana MP, Zug KA (2013). Methylisothiazolinone (Contact Allergen of the Year). Dermatitis 24:2–6. View →
• Bruze M, Engfeldt M, Gonçalo M, Goossens A (2013). Recommendation to include methylisothiazolinone in the European baseline patch test series. Contact Dermatitis 69:263–270. View →
• Commission Regulation (EU) 2016/1198: methylisothiazolinone no longer permitted in leave-on cosmetic products from 12 February 2017. Read it →
• Commission Regulation (EU) 2017/1224: rinse-off limit reduced to 0.0015% (15 ppm) from 2018, following SCCS opinion SCCS/1557/15. Read it →

Find out more

• Phenoxyethanol: the paraben replacement, and is it safe?
• Cocamidopropyl betaine: the "allergen of the year" that probably isn't
• Triethanolamine: dangers, side effects and is it safe?
• Diethanolamine (DEA) and cocamide DEA: dangers and is it safe?
• Commercial soap ingredients: what's really in your bottle

This article is general information, not medical advice. If you have a skin reaction that doesn't settle, see a doctor or dermatologist and ask about patch testing.

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