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​Ingredient Spotlight: Methylisothiazolinone

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In this article, I’ll be sharing some information about the ingredient Methylisothiazolinone - commonly known as MI. Check your labels - perhaps it's listed there?

What is MI?

MI is a synthetic preservative found in many consumer products, including cosmetics, pharmaceutical products and household cleansers, as well as industrial products and settings like jet fuels, printing inks and cooling tower water.


What are some specific examples of products containing MI?

You can find MI in makeup items like foundation, eye shadow and mascara, as well as personal care items like moisturisers, sunscreen, lotions, gels, mouth wash, shampoos, soaps, body wash and wet wipes, including baby wipes. It’s also used in some over-the-counter and prescription medicines, along with household cleaning products, laundry detergents, polishes, adhesives, pesticides and so on. Yes, it’s just about everywhere!

So what are the safety concerns surrounding MI?

Two of the main concerns surrounding MI are:

  • Neurotoxicity – lab studies on the brain cells of mammals suggest that MI may be neurotoxic.1
  • Skin sensitisation and allergies – MI has exhibited skin sensitisation effects and may also cause systemic acute toxicity and local effects such as eczema and contact allergy reactions.2

How bad is MI?

As far as allergic reactions are concerned, the increase in the number of cases of allergic contact dermatitis has been quite dramatic in recent years.

  • In 2011, Drs Jennifer Cahill and Rosemary Nixon (Dermatologists with the Skin and Cancer Foundation Inc.) began including MI in their baseline patch test series for allergies, following European reports of increasing cases of MI contact allergy. The rate of positive test reactions to MI in 2011 was 3.5%, increasing to 8.4% in 2012 and increasing further in 2013 to 11.3%. The doctors declared in 2013 that “MI is now the most common cause of allergic contact dermatitis in our patient population.” Dr Cahill also wrote that “interestingly it is parents using baby wipes on their children who are presenting with hand dermatitis, although it is likely that allergic contact dermatitis involving the groin in children may not be diagnosed accurately.”
  • The allergic reaction of people to MI has been described as an ‘epidemic’ and the American Dermatitis Society named MI ‘Allergen of the Year’ in 2013.
  • According to Safe Work Australia, MI is recommended for classification as hazardous with the risk phrase ‘Causes burns’. MI has also been recommended for classification as highly corrosive and is expected to be severely damaging to eyes in its undiluted form.
  • In Australia, the Occupational Dermatology Research and Educational Centre has spoken to the ACCC addressing the effects of MI as a consumer safety issue. They have also alerted the National Industrial Chemicals Notification and Assessment Scheme (NICNAS).

What about MCI (Methylchloroisothiazolinone)?

Methylchloroisothiazolinone is in the same group of preservatives (isothiazolinones) as MI. Since the 1980s, MI has often been combined with MCI in a blend of 1:3 (1 part MI to 3 parts (MCI). This is because MCI is also a strong skin sensitiser and is not allowed to be used in cosmetics on its own – only with the MI blend in the aforementioned ratio.

The passage of time, however, has seen the production of more products with MI alone and in higher concentrations.3 This is likely due to safety concerns about MCI and also the continued fall from grace of the once popular parabens.

What about Government regulation?

Trying to determine the exact status regarding Government regulation of MI in various parts of the world can be confusing, mainly because there have been so many concerns raised as to its dangers and so many proposals to amend the generally accepted maximum concentrations in both rinse-off and leave-on cosmetics of 100 ppm (parts per million) or 0.01%. Interestingly, in 2018, Cosmetics Europe recommended discontinuing the use of MI in cosmetics altogether.

From what I can tell, the current status is:

  • Canada - has reduced the maximum concentration allowed in cosmetic formulations to 15 ppm or 0.0015% and there are recommendations that it be banned completely from leave-on cosmetics. This same concentration applies to formulations containing a combination of MI and MCI.
  • European Union - in 2016 leave-on cosmetic products containing the combination MI/MCI were banned from the European market. In 2017 MI used on its own was banned in leave-on cosmetic products. In 2017 the maximum concentration of MI allowed in rinse-off products was reduced to 0.0015% (15 parts per million).
  • Australia - in 2017 there was an application to the TGA (Therapeutic Goods Administration) to limit the allowed concentration of MI in rinse-off cosmetic preparations or therapeutic goods intended for topical rinse-off application to 0.0015% in line with the EU. This was to come into effect in 2018. In other preparations not intended for direct application to the skin, the maximum concentration remains at 100 ppm (0.01%).

Conclusions and take-aways

There is so much information available online about both MI and MCI and all the safety concerns and different regulations around the world. It can be quite confusing but you should do your own research if you are concerned about this ingredient.

The general consensus appears to be that:

  • current clinical data indicate that 100 ppm MI in cosmetic products is not safe for the consumer.
  • For leave-on cosmetic products (including 'wet wipes'), no safe concentrations of MI for induction of contact allergy or elicitation have been adequately demonstrated.
  • For rinse-off cosmetic products, a concentration of 15 ppm (0.0015%) MI is considered safe for the consumer from the view of induction of contact allergy. However, no information is available on elicitation.

Of course, preservatives are necessary in products containing water. No-one wants bacteria or mould in their cosmetics. That would definitely be unsafe.

As far as Methylisothiazolinone is concerned, you can make up your own mind but, for me, MI is a bit fat NO. No, thank you. Maybe because I have sensitive skin, I don't know. I wonder how many people have developed rashes and wondered what caused them? I know that's happened to me in the past. But with everything I have read about this ingredient, I'm not convinced that it has any place in cosmetics. And I know that no product containing MI would ever be granted organic certification so that's another factor to consider.

Baby wipes featured quite a lot in my research. Even the ones with label claims of 'natural', 'organic' or 'gentle' often contain MI or MI/MCI so beware.

Well, all I can say is, if parabens are pretty much out and MI/MCI are on their way out, good luck to the manufacturers finding the next popular preservative. Let's hope they can improve the safety aspect in the future.

1 EWG’s Skin Deep Cosmetics Database.

2 Therapeutic Goods Administration (TGA)

3 Hindawi Dermatology Research and Practice

The author is not a health professional. Any information or advice in this article is of a general nature only and taken from the author's own research of information readily available online. Nothing in this article is intended to diagnose, treat, cure or prevent any disease. For medical advice regarding your own personal circumstances, it is recommended that you contact your GP or other healthcare professional

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