2-Bromo-2-Nitropropane-1,3-Diol (Bronopol)

What is bronopol?

Bronopol (INCI name for 2-bromo-2-nitropropane-1,3-diol) is a broad-spectrum preservative used in cosmetics and industry, effective against bacteria at very low concentrations (0.01–0.1%) across a wide pH range. It belongs to the formaldehyde-releasing family: it breaks down — especially with water, light, or heat — to release formaldehyde, which provides much of its antimicrobial punch and is the source of its allergy risk.

It carries a second, separate concern: as a nitrosamine precursor, it can react with secondary amines in a formula to form N-nitrosamines (potential carcinogens), so its use alongside amine-containing ingredients is restricted.

Why it causes reactions

Bronopol causes allergic contact dermatitis via the formaldehyde it releases — that formaldehyde binds skin proteins to form haptens, triggering a delayed (Type IV) reaction in sensitised people. It's a standard patch-test allergen (including on the TRUE test panel). A few specifics:

• Cross-reactivity: a positive usually predicts sensitivity to other formaldehyde releasers and sometimes free formaldehyde.
• Irritation can also occur on broken skin or at higher concentrations.
• Despite the bromine in its name, the allergy is a formaldehyde allergy — relevant cross-reactions are within the releaser family, not other bromine compounds.

How to spot and avoid it

1. Read labels for Bronopol or 2-Bromo-2-Nitropropane-1,3-Diol.
2. If you react, avoid the whole releaser group — DMDM hydantoin, quaternium-15, imidazolidinyl/diazolidinyl urea, sodium hydroxymethylglycinate — plus free formaldehyde.
3. Prioritise leave-on products (more contact time) when scanning.
4. Prefer non-releaser preservation — phenoxyethanol, ethylhexylglycerin, caprylyl glycol.

When to see a dermatologist

A persistent, itchy rash that tracks with lotions, shampoos, or wipes is worth patch testing — bronopol and formaldehyde are on standard series. Confirming it lets you clear the entire releaser family from your routine, which is far more effective than avoiding one name at a time.

The bottom line

Bronopol is a potent formaldehyde-releasing preservative with an extra nitrosamine caveat — which is why it's increasingly avoided. For formaldehyde-sensitive people it's one to skip, along with the rest of the releaser family; for everyone else, it's simply an older preservative that newer, gentler systems have largely replaced.