I get a lot of traffic to my post about the combination of Methylisothiazolinone and Methylchloroisothiazolinone. If you read all the comments it gets, you’d probably get the impression that this preservative system had a really big problem with sensitisation. This would be pretty misleading. In real life products preserved with these ingredients don’t generate unusually high numbers of customer complaints, and published surveys report low levels of sensitisation to them.
The problem is basically one of success – because they don’t have too much of a problem they get used over and over again in product after product. This leads to larger exposure ensuring more reports – comments on my blog post being a good example.
One possible way that this problem might be reduced is to drop the Methylchloroisothiazolinone and just use the Methylisothiazolinone. I wasn’t particularly struck by this idea personally. It doesn’t help the people who are already sensitised – I don’t think they would want to risk trying a single one when they already know that at least one of the pair gives them a problem. In fact they are probably sensitive to both anyway.
But my misgivings aside, a supplier of preservatives has been promoting Methylisothiazolinone on its own. I don’t know how many companies have given it a try. It is easy to tell whether it works as a preservative – you just have to inject some micro-organisms into a product and see if the preservative kills them off. It is much less easy to tell whether the level of sensitisation reactions has been affected. Reactions as so rare you would have to recruit an enormous panel to assess the level of reaction. Basically the only way to find out is to launch a product and wait for the complaints.
It is possible that some companies have done exactly this, judging by this report in the Daily Telegraph.
The implication of this report is that there has been a large increase in allergic reactions over the last couple of years. Unfortunately it is impossible to tell what is really going on from reading that article. What we really need to know is what proportion of the users of a product preserved with Methylisothiazolinone alone have a reaction compared to the combination. Without that information all we can do is speculate.
As a formulator I really want to know the answer. Obviously you want to use the best option. It is a shame that the journalist has chosen to make it a scare story. But it is also a shame that we folks in the cosmetic industry are so dependent on such a small number of preservatives.
There are a lot of people out there who would really appreciate more choice.