MI Free Paints (MIT / MI / BIT - thiazolinone free paints)
The following wall paints, wood oils and finishes are entirely free from MI (MIT/BIT)
MI = Methylisothiazolinone
MIT = Methylisothiazolinone (sometimes written like this in European labelling)
BIT = Benzisothiazolinone
All three are isothiazolinone preservatives. They’re added to water-based paints to stop mould, bacteria, and yeasts growing in the tin (imagine a pot of yoghurt left on the shelf otherwise).
These preservatives are used at trace levels (fractions of a percent), but they’re potent allergens. MI in particular has been at the centre of big debates in cosmetics and paints it caused widespread cases of contact dermatitis in the 2010s, especially for decorators exposed to freshly applied paint. BIT is generally considered the “less sensitising” of the group, but it’s still allergenic.
Options if you want to avoid them
Lime-based, clay, or mineral silicate paints often don’t need these preservatives, since their high alkalinity is naturally biocidal.
Why thiazole chemistry shows up in paint
Water-based paints are basically a combo of water + starches/cellulose + plant oils + pigments + minerals. Left alone, that’s microbial heaven. Chemists needed preservatives that were powerful in very small doses, stable in water, and cheap. They turned to isothiazolinones, a branch of the thiazole family, because their sulphur - nitrogen - oxygen ring messes with bacterial and fungal enzymes so effectively that even a few parts per million will sterilise a paint pot. Their whole job is in-tin protection, not on the wall, once the paint dries, they’re largely locked in place.
How it plays out in real products
Mainstream acrylic paints (big DIY brands) nearly always contain MI, MIT or BIT. That’s why you’ll sometimes see skin-reaction warnings on tins.
Eco/natural paints try to avoid them.
Lime, clay, silicate paints are naturally alkaline → microbes can’t grow, so no need for thiazole-derived preservatives.
Plant-based emulsions may use BIT in very low amounts (legally mandated shelf-life) or skip preservatives entirely, which is why some natural paints come in smaller tins or have shorter storage advice. It is usually the pigments that contain it, rather than the base paints.
These paints are all MI / MIT / BIT free:
