Want to make a microbiologist's eyes roll? Just whisper the words "kills 99.9 per cent of household germs".
This marketing mantra of the cleaning products industry might inspire confidence in consumers but it can also create a false sense of security, says Professor Liz Harry, director of the ithree institute (infection, immunology and innovation) at the University of Technology Sydney.
"It's not the percentage of germs that matters but the absolute numbers – if there are billions of germs and you kill 99.9 per cent of them, the remaining one per cent can still represent a lot of germs – and you don't know whether they're harmful or not," she says.
If it were up to Harry, we wouldn't be cleaning our homes or our hands with so many antibacterial products at all – at least not if we want to avoid a backflip to life without antibiotics. We might think that widespread use of antibiotics and antibacterial products gives us the power to eradicate harmful germs but in fact we're empowering them to outsmart us.
"Bacteria have been around for billions of years – they've learned to defend themselves and have developed genes that resist antibiotics as well as genes that resist antibacterial chemicals. They can also spread these genes to other neighbouring bacteria within minutes," Harry explains.
In other words they don't just pass the ability to resist antibiotics and antibacterial chemicals from one generation of microbes to another – they pass it on to the neighbours too.
"There are times when you need antibacterial solutions but we don't need to spread them around willy nilly. If you use a lot of antibacterial products you risk enriching your home with more bacteria that are resistant to antibiotics and antibacterial chemicals," she adds.
"The US has banned a number of antibacterial chemicals including triclosan for domestic use because they're not needed in the home and their overuse can make them less effective in hospitals. I think we need to be stricter about regulating some of these chemicals in Australia."
The overuse of antibacterial products can also kill off beneficial bacteria.
"Microbes are part of our world. Most of our body is made up of microbes – and we need most of them to live," Harry says. "They play a role in our defence systems – they stimulate the immune system and help protect our skin, for example."
Although it's still in the 'more research is needed' department, some research suggests that exposure to a wide variety of microbes in childhood may pay off in less allergy and asthma later on.
A recent US study of babies growing up in inner city areas found that those exposed to rodent and pet dander and a wide variety of household bacteria in the first year of life were less likely to suffer from allergies and asthma later on. Other research has linked overuse of antimicrobial products to allergic symptoms in children – a 2014 study of more than 25,000 Korean children found that high exposure to antimicrobial products was associated with wheezing and allergic rhinitis (hay fever) while a study of Norwegian children linked high concentrations of the antibacterial triclosan in the urine to rhinitis.
"Antibacterial chemicals are effective – but we use them too much and they persist in the environment," says Professor Peter Collignon from the Australasian College of Infection Prevention and Control.
Like Liz Harry, he thinks antibacterial products can give us a false sense of security and risk making us less scrupulous about things like handwashing with regular soap and refrigerating food promptly.
"In most situations hot soapy water will do the job along with elbow grease – it's the vigorous physical scrubbing that helps remove bacteria. Alcohol hand rubs are useful when someone is sick or when you're travelling. Vinegar is a useful disinfectant and like alcohol is biodegradable," he says.
However vinegar won't kill salmonella so chopping boards or surfaces used for raw meat, poultry or fish need cleaning with hot soapy water, he adds.
As for kitchen sponges, wash them frequently with hot soapy water (or in the dishwasher) and let them dry out before use.
And it goes without saying that we hand wash frequently – and not with a cursory rinse under a cold tap.
"Use hot water and normal soap, not antibacterial soap – and scrub your hands like a surgeon," Liz Harry says.