Ever wondered about the claim on some spray cleaners of a 99.9% killing rate of all germs. It was a question that was bugging retired medical laboratory worker Graeme Broad, so he asked Fair Go to investigate.
Broad believed the claim was "too specific", asking "what do they test against? And what about the 0.1% that aren’t killed, how dangerous are they?"
Products that claim antibacterial action specify the micro-organisms they’re tested against in the small print on the container’s label. Most mentioned only three or four micro-organisms. Based on this, Broad was concerned the 99.9% kill rate claim was too generous. However, the manufacturers defended the claim, saying it would be impossible to test a product against the trillions of micro-organisms that exist, so the international regulatory standards allows for testing against so-called “indicator” microbes.
If the product kills these then it’s accepted it will also kill all other micro-organisms of the same class. The manufacturers also explain that a 100% kill rate can’t be claimed due to testing limitations of standard methods.
A leading expert in microbiology doesn’t dispute these explanations but is worried consumers may be more obsessed with killing germs than they need to be.
Otago University’s Professor Kurt Krause explains that all cleaning products, including soap and water, will kill enough germs for surfaces to be hygienic, and that humans aren’t designed to live completely germ-free lives.
"That's not to say that there aren't situations where it’s good to use commercial products, for example, if someone in your house has been in contact with harmful bacteria then you may want to sanitise that area, but in general if you're cleaning up at home my feeling is that soap and water works just as well."
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