MI in paint

One of the most surprising things about blogging is how much you learn.  A good example arrived in my inbox yesterday.  I have just started a newsletter for people with sensitive skin, largely because I get a lot of people getting in touch looking for information about it, and in particular sensitivity to methylisothiazolinone or MI.  This is of course of no interest at all to the 99.9% people who don’t have a problem with it, so I thought a newsletter was a good way of giving them the information they want without devoting too many blog posts to it.  But a list member drew my attention to something simply too interesting not to share it.

I am probably the worst person in the world to talk about paint formulations.  Paint isn’t much like cosmetics, but there are some common features.  We use some of the same techniques and similar raw materials.  This means that as a cosmetic chemist I sometimes run into the simple but honest folk who formulate paints at conferences and trade shows.  So I am vaguely aware that there are some paints that need to be preserved from microbial contamination.  I wouldn’t have guessed that they use MI for this purpose, but I can imagine that it would probably work quite well.  So I wasn’t surprised to hear that it is used in paints.  And if your painting technique is anything like mine, you can easily see how that would lead to problems for people with an MI sensitivity while painting.

What was much less obvious was what would happen as the paint dries.  My respondent found that she reacted to the atmosphere in the rooms once they were painted.  As the paint dried the preservative dried out as well and contaminated the air.  She did some research and it turns out that while this is a rare problem, she was not alone.  Other people had had the same experience.  She also found a solution.  The MI on the walls can be neutralised with sodium bisulphite, as detailed in a paper in the journal Contact Dermatitis.

It is a shame that the rules about disclosure of ingredients don’t apply to household products in the same way that they do to cosmetics, so people can be pre-warned of the hazards.  In fact, on a practical level I think the optimum approach would be to list preservatives and only preservatives on everything.  I find really long cosmetic ingredient listings confusing and I’m a chemist.  I am sure there are many members of the public who would much prefer it if only materials that are likely to cause problems were put on packs.  And whatever the system, it makes most sense for it to be applied universally across all product types.

But anyway, thanks to Christine for teaching me something.  If you are interested in sensitive skin and you haven’t yet signed up for my newsletter on the subject you can do so here.

sensitive skin newsletter


Airborne contact dermatitis from methylchloroisothiazolinone in wall paint. Abolition of symptoms by chemical allergen inactivation


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