Methylchloroisothiazolinone, methylisothiazolinone …

… benzisothiazolinone, octylisothiazolinone. Four preservatives with very long names that most have never heard of, but together, they’re responsible for one of the most significant allergy epidemics in recent decades — and they are also the subject of my latest book, called Living with Methylisothiazolinone Allergy.

MCI, MI, BIT and OIT, as they’re more conveniently also known, are used widely in household detergents, fabric softeners, glues, inks, paints and many other chemical products and solutions which contain water, where they act as highly effective preservatives.

MCI and MI are also common preservatives in cosmetics. Since 2017, in the EU, their use has been severely restricted, and they can now only be used in low amounts in ‘rinse off’ cosmetics (such as shower gels and shampoos) but — unlike in the US and many other countries — not ‘leave on’ cosmetics (such as moisturisers and mascara).

Their previous use in leave-on cosmetics has been largely to blame for up to 1.5% of the population becoming sensitised to them. They include Sarah, who runs the popular ‘free from’ blog, Sugarpuffish, and who was diagnosed via patch testing — the only recognised way of being sure you are sensitive to the ‘isothiazolinones’, as they are collectively known.

The cosmetics restriction is expected to take the edge off the epidemic, but sensitisation through exposure to household chemicals, and indeed occupational exposure in factory or production workers, will probably continue unabated unless alternative preservatives can be found and become popular.

I wrote the book to address the needs of people with this allergy, and it supplements the blog I launched a few years ago — called MI Free — which has a substantially bigger subscriber following than this blog!

There are so many niche and unusual allergies out there, which even specialists know little about managing on a day-to-day basis, and this is just one of many dozens with which many people struggle …

If you experience unexplained angry red rashes, extreme itching, irritated or inflamed skin, especially on the hands and around the eyes, and worry whether it could be an isothiazolinone allergy — it could be. Up to 10% of those with eczema could be affected.

But it could also be an allergy to another preservative, to a fragrance, to another cosmetic ingredient, to several cosmetic ingredients, or to none at all, and it may be something else entirely. See your doctor, or a dermatologist. Experimenting with the products you use in your bathroom and kitchen may help, but if you don’t know what you’re dealing with, then it’s just a matter of pot luck whether or not you improve or manage to avoid your triggers …

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