There’s a new paper out with some numbers from dermatology clinics about reactions to methylisothiazolinone (MI). Dermatologists regularly patch test people to discover what they are allergic to. This involves applying a set of common materials that tend to provoke allergic reactions to the skin, and seeing which ones the individual reacts to.
The main motivation for doing this is to help the individuals involved, but it also allows an idea to be got of what kinds of things are causing problems. MI does seem to be getting higher numbers than it used to. In this latest paper it had hit 6%. This is of course, 6% of people who suffer from allergic skin reactions severely enough to be referred to a dermatologist.
This is not going to give you much of an idea of how many people overall are allergic to MI, a figure nobody knows. I am dreading a journalist getting hold of this and assuming that it means that 6% of everybody. If that were the case there would be millions of people suffering from MI in the UK alone. In fact that the vast majority of even the people with very sensitive skin don’t have a problem with MI.
To put these figures in context, this is the highest number I can remember for a cosmetic preservative from a study of this kind, but not by much. They are usually somewhere between 2% and 4%. The biggest factor always seems to be how widely the preservative is used. I would expect that the figure will start to come down now that MI use has been restricted to rinse off products in the EU.
For me the most surprising thing about the paper was its title. “The epidemic of methylisothiazolinone: a European prospective study” to give it in full. I don’t think there is any way you can describe the recent uptick in MI reactions as an epidemic. In some ways, it would be easier for all concerned if it were – at least then we could just ban it.
Incidentally the word prospective here means that they were actively seeking out MI sensitivity. This involved applying a level way higher than is used in cosmetics. There is no way around this: you have to give a decent dose to make sure you pick up something. But it also means that the study is quite likely to be overstating the numbers of people who are reacting. The point of this kind of work is to look for trends so you sort of have to do it that way. It is scientifically justified, but I am a bit wary of how it might get reported.
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