Does MI Cause Developmental Problems?

MI development problems

There are an interesting couple of points in the comments thread on my blog post asking for MI not to become a scare story, from Suzanne. She has drawn my attention to a paper from 2012 that details developmental problems in tadpoles exposed to MI. She concludes from this that MI is potentially unsafe for humans as well and asks what the liability is for companies that continue to use it now that this risk has been identified.

There are two quite different questions here. The first one is the scientific one. How seriously should we take the data in this paper? The second one is social. What do we as a society do with information like this?

The scientific question is the easier one. The fact that MI can have an adverse effect on the development of an amphibian is not exactly good news and is something that needs to be taken seriously. But tadpoles are very small and live in an aquatic environment. So it isn’t immediately obvious that what happens to them will be applicable to humans. There is also the question of the dose. Unfortunately I have only been able to read the abstract – this is a paper that is behind a paywall. But I do know that MI is used at extraordinarily low levels in cosmetics so I would be very surprised if the tests on the tadpoles were done at anything like as low a level as the average consumer is exposed to.

It is necessary to keep an open mind and if new risks become apparent then maybe MI isn’t as safe as it currently appears. But there are problems with every preservative and to my mind MI is still the safest option overall. I still use products preserved with it without any worries myself.

The question of liability for companies using it is a lot more intangible. Ultimately, we make decisions like this as a society. If Suzanne is convinced that the use of MI is wrong, then in theory she could bring an action herself against a company selling a product using it. And at the end of the day the question of whether or not they have committed an offence would be decided by a jury. So the final word on this would end up in the hands of twelve randomly selected members of the public.

What would their verdict be? I have no idea. I know that I personally would acquit them. But I am not an unbiased person in this case and would probably be thrown off the jury before the trial started.  What level of risk is considered acceptable is ultimately something that society as a whole decides.  It isn’t a question for experts.

There is no precedent in British law for such a case that I can think of off the top of my head. There is the ongoing talc story in the US at the moment, which suggests that the public are not very sympathetic to big companies placing them at risk. So if there is indeed a proven problem from MI then maybe companies will one day find themselves in the dock. I would be surprised, but it wouldn’t be totally out of the question.

But back to the science, and I have to say that if MI is shown to be unacceptably risky then all the other preservatives used in cosmetics would be equally suspect. In effect, if juries won’t tolerate any risk at all then every cosmetic will have to be preservative free. This would mean that many cosmetics would only be available chilled and would only last a week or so even in the fridge. That would be a pretty big change to the way we live.

Note – I am assuming that everyone now knows that MI stands for methylisothiazolinone.


Neuroscience. 2012 Mar 15;205:194-204. doi: 10.1016/j.neuroscience.2011.12.052. Epub 2012 Jan 4. Abnormal visual processing and increased seizure susceptibility result from developmental exposure to the biocide methylisothiazolinone. Spawn A, Aizenman CD.

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