Benzisothiazolinone allergy

MI Free December 1, 2021 8 Comments

The BIT molecule (Attribution: Jynto, CC0, via Wikimedia Commons)

Benzisothiazolinone (BIT), like its better known ‘siblings’ methylisothiazolinone (MI) and methylchloroisothiazolinone (MCI), is a member of the ‘isothiazolinone’ group of highly effective preservatives, which between them have contributed towards a worldwide epidemic of allergic contact dermatitis in recent decades. 

In the UK, EU and Australia / New Zealand, BIT is not permitted in cosmetics / toiletries.

That said, there have been occasional incidents of products containing BIT and later withdrawn. One from the UK was Ecoleaf’s Hand Soap, which we reported and covered here in 2019, and there was also a case from Australia, where the preservative was used in a cleanser by Skin Physics, and may have been involved in the adverse reaction experienced by a customer from New Zealand who used it in 2017 — see the report on the Stuff news site here.  

But these are rare cases.

Also rare is its use in cosmetics in the US — but unlike in most other Western countries, it is permitted in America. Until fairly recently, you could find BIT used in some of Puracy‘s hand soaps (they now appear to have been reformulated) and it still seems to be used in Earthy Spa‘s Unscented Natural Hand Soap. There may well be others.

In general, though, you will find BIT principally in household detergents (where it is generally clearly declared in ingredients) and paints.

In this latter case, it is unlikely to be labelled, but you should always assume that one or more of the isothiazolinones is present in all prepared paints, until you can confidently confirm the contrary. 

Changing picture of sensitisation

What is currently interesting about benzisothiazolinone from an allergy perspective is that researchers are beginning to recognise that it may become an increasing problem in its own right, with the potential in future to overtake MI and MCI. 

Trends in Preservative Allergy: benzisothiazolinone emerges from the pack is a new paper just published in the journal Contact Dermatitis (click here to read the abstract). 

Researchers collated almost eight thousand patch test results between the years 2011 and 2019, and found that the rate of MI allergy detected fell from 10% in 2013 to 2% in 2019, and of MCI allergy from 8% in 2014 to 1.5% in 2019. Meanwhile, BIT allergy rates rose from under 0.3% in 2014 to 3.5% in 2019. (All figures rounded up / down. Bear in mind these are rates of patch-tested individuals, suspected of having contact dermatitis, and not the wider general population.)

The researchers put this down to the increased use of BIT in household products. This is undoubtedly true. As MI and MCI have ‘suffered’ from the negative publicity associated with the allergy epidemic in recent years, some manufacturers will have certainly turned to what they view as a more benign alternative in BIT instead.

However, the increased restrictions being placed on MI and MCI in cosmetics are also likely to be a factor. The population’s exposure to isothiazolinone preservatives will have shifted somewhat, from MI / MCI towards BIT (and possibly other isothiazolinones, such as octylisothiazolinone or OIT, which is also widely used in detergents). 

This research from Belgium, also recently published in Contact Dermatitis, supports this view. It notes a “remarkably high number of patients” co-sensitized to both MI and BIT — which should be “the focus of future research” — and that leave-on cosmetics have almost entirely disappeared as sensitization sources. 

Another reason for the increased rate of BIT allergy may simply be due to the fact that more patch testing centres test for it, and that it is now more commonly added to panels. 

What to do if you have BIT allergy

BIT allergy is an isothiazolinone allergy and if you have an isothiazolinone allergy you should avoid all isothiazolinones.

Even if you do not react to one or more, needlessly exposing yourself to close relatives of the isothiazolinones you do react to, merely increases your chances of becoming sensitised to those as well, which may result in more severe reactions to future accidental exposures. 

Unless explicitly stated otherwise, all information on this website applies to all isothiazolinones, and the “MI Free” products in the product lists under cosmetics and household are all free of BIT and other isothiazolinones too.

And finally, as I received a query on this matter recently, I ought to clear this up: My book (pictured right, and available from Amazon), despite its name, covers not only allergy to MI but also to BIT, and to other isothiazolinones too — they’re a close ‘family’ of chemicals, one in which they are all, without exception, black sheep to be avoided …