Benzisothiazolinone allergy

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That said, there have been occasional incidents of products containing BIT and later withdrawn.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 … 


  1. Margaret Willers

    I am having knee surgery tomorrow. They ordered me to wash my knee for three days in advance with Hibiclens. After one wash, my eyes swelled shut and I was trying to scratch my skin off. It is full of one of isothiazolinones. And their intention was to use a concentrated version all over me before the surgery. Be careful out there. Doctors dont appreciate the problem. My allergy was on my chart and I was still prescribed it.

    1. MI Free (Post author)

      What a horrid experience. That’s incredibly careless of them. Do check what they’ll be using on you in its place. Hope all goes well.

  2. Dana Todd

    I’m ever so aware of the dangers of BIT as I write this today…I went to the movie theater over the weekend and didn’t realize that I was inhaling air and fabric deodorizer (Febreze) for a 3-hour movie, resulting in a severe systemic contact dermatitis event. For me, that means I’ve had 5 days of crippling back spasms as it works its way out of my system. When I get an airborne exposure like this, it usually goes to my nervous system first. It’s excruciating, even muscle relaxers and painkillers don’t help reduce the impact. I just have to wait it out, and hope I don’t get any more BIT exposure in the near future. It’s in so many household cleansers in the US as well, it’s really hard to avoid in people’s homes.
    I’m so frustrated with the regulators on this topic. I had lobbied hard to have BIT limited or banned, but they just ignored all our concerns and went with the current guidance. 🙁

    1. MI Free (Post author)

      This is so awful. I am so, so sorry you suffered so badly. Thanks for sharing this. Important that we keep putting these experiences out there as much as we can. I’ll share it on social media in the week so more see it. Hope you’re now fully recovered – and sorry I didn’t see the comment earlier. Alex.

    2. Veikko Aallonhuippu


      I am a hypersensitive person from Finland.
      Dana Todd you say you have päin in your body after exposure to MI inhaled. Can you tell More about your symptoms that are systemic?
      I think I have had these symptoms for a long Time and I have Been avoiding The smell of these chemicals by instinc. I feel nausea and burning in my airways from Fairy, Omo, Febreze and many other products. Last week I had severe reaction from Jonhson laminate floorwash. I got red and swallowed especially on hands, feet and face. I got chills and goosebumps. Like very strong Flushing sensations all over My body and all the hairs stood up. Felt like I had fever and was sweating like Hell. Normal body temperature. Prednisolon 40mg helped some.
      After that I feel like having The same symptoms from Even a little air contact.

      Thanks and stay healthy!

  3. June Sam

    Beware ! Most doctors or health people do not check for these things and we are the ones who suffer !

  4. M

    Does anyone else feel ill after being inadvertently exposed to Febreze? It’s difficult to avoid due to being airborne and I’m guessing it’s “leave on” once it has landed or been sprayed on a surface. I contacted the manufacturers twice but haven’t had a reply.

    1. MI Free (Post author)

      On their site they say they use benzisothiazolinone in their ‘Air Effects’ –


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