Chapter 6: Preservatives
Benzalkonium chloride
- Poison schedule (Australia)
- Made from a hazardous chemical
- Contaminant risk
The worst fact: it has been linked to asthma in cleaners and nurses who use it at work, and Japan's government classes it as a cause of asthma. In Australia it's a Schedule 6 Poison above 10% (Schedule 5 above 5%), and household cleaners can contain up to 20%.
Why brands use it: it kills many germs at low levels. It's the main active in "alcohol-free" hand sanitisers, and the most common preservative in eye drops.
Take care if: you have asthma, use eye drops often, or wear contact lenses. Eye drops with it have been reported to damage the surface of the eye with frequent or long use. Don't mix it with soap, because soap cancels it out.
Comes from: a fatty amine reacted with benzyl chloride. Australia classes benzyl chloride as "May cause cancer". That doesn't mean it's in the product, but it's not a great starting point for something you clean with.
Myth check: "it kills everything": no. It doesn't kill spores, and it's often weak against some viruses.
Contaminants: benzyl chloride, benzyl alcohol and benzaldehyde can be left over from making it. They're unlikely in a well-made product, but it's a factor you can't see on the label.
Fair to say: the asthma link rests on a small number of cases. The US FDA hasn't banned it in hand sanitisers. It has asked for more safety data, as it has for alcohol.
Correct as of November 2026. What the badges mean
Sources
- Australian Government. Poisons Standard October 2026 (SUSMP), F2026L01327. Entries: methylisothiazolinone, methylchloroisothiazolinone, 2-phenoxyethanol, benzalkonium chloride. legislation.gov.au
- Safe Work Australia. Hazardous Chemical Information System (HCIS): classifications for each chemical and for benzene, ethylene oxide, toluene, phenol and benzyl chloride. hcis.safeworkaustralia.gov.au
- European Medicines Agency. Questions and answers on benzalkonium chloride used as an excipient (EMA/CHMP/495737/2013, 2017). ema.europa.eu
- Japan NITE. GHS classification results for benzalkonium chloride (FY2017). chem-info.nite.go.jp
- Purohit A et al. Occupational asthma from benzalkonium chloride. Int Arch Occup Environ Health 2000 (PMID 11007347).
- Santos, Li, Rustum. Impurities in benzalkonium chloride. Chromatographia 2010;71:499.
The full source list is at the end of Chapter 6.