What Is Benzisothiazolinone (BIT)?
In plain English: Benzisothiazolinone is a synthetic preservative from the isothiazolinone family, used to protect water-based cleaners, detergents, paints, and adhesives from bacteria and mold. It is an established skin sensitizer whose allergy rates have risen sharply in recent years.
Also listed as: BIT, 1,2-benzisothiazolin-3-one, 1,2-benzisothiazol-3(2H)-one, isothiazolinone preservative
The honest science
Benzisothiazolinone (BIT) is a close cousin of methylisothiazolinone and works the same way, killing bacteria and fungi to keep a water-based formula stable 1. It shows up often in cleaning products, laundry detergents, paints, and adhesives.
BIT is a recognized contact allergen. Regulators classify it as a skin sensitizer, and in the EU it has been categorized as a category 1A skin sensitizer with a labeling limit tied to that hazard 1. A 2025 analysis in Contact Dermatitis found that patch-test reactions to BIT climbed from about 0.3% or lower in 2014 to roughly 5.0% in 2023, with detergents and paints among the most common exposures, making it a preservative allergy "on the rise" 2.
Keeping this in proportion: the documented concern is allergic contact dermatitis, a red, itchy, sometimes blistering rash in sensitized people, not systemic poisoning at product-use levels 1. BIT is banned from cosmetics in the EU but still permitted in cleaning products and in personal care in the US and Canada, which is part of why cleaning-product exposure matters 12. If your hands react to a detergent, BIT is worth checking for alongside MI and MCI/MI.
Where you'll find it
- all-purpose cleaners
- laundry detergent
- dish soap
- paints and coatings
- adhesives and glues
The safer-swap angle: Because BIT sits in the same allergy-prone family as MI, avoiding all isothiazolinones is the cleanest path for reactive skin. Ecolosophy's small-batch concentrate is made with care and skips them.
Frequently asked questions
Is benzisothiazolinone the same as methylisothiazolinone?
They are different chemicals but belong to the same isothiazolinone family and share the same core concern: skin sensitization. People allergic to one may react to others in the group.
Why is BIT allergy increasing?
As other isothiazolinones were restricted, BIT use grew in cleaning products, detergents, and paints. Patch-test data show reactions rose from under 0.3% in 2014 to about 5% in 2023.
Is BIT allowed in the US?
Yes. It is banned from cosmetics in the EU but still permitted in cleaning products broadly, and in personal care products in the US and Canada, so reading labels matters.
Sources
- Benzisothiazolinone: Allergic Contact Dermatitis — DermNet NZ
- Trends in Contact Allergy to Preservatives From 2014 to 2023: Benzisothiazolinone on the Rise — Contact Dermatitis (PMC)
Ingredient safety data changes as new research is published, and product formulas change over time. Always read the current label and check primary sources.
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