Why antibiotics shouldn’t be in soap

You might assume that a soap or a cleaning product labelled as “antimicrobial” or “antibacterial” is a safer, more hygienic option. But there’s no evidence these substances do anything to improve hand hygiene, and they could be contributing to the much more dangerous problem of antibiotic resistance.

In 2016, the US Federal Drug Administration banned 19 of these antimicrobial compounds in household soaps, on the basis that they didn’t clean any more effectively, and they may have adverse side effects.

In Australia, soap marketed as antibacterial or antimicrobial may still contain these compounds; there’s no formal regulation of them. There are calls from experts in Australia to ban the compounds in commercial soaps as well, for similar reasons. They don’t make soap more hygienic, and – more worryingly – they may contribute to antibiotic resistance.

So why don’t these compounds help to clean our hands – and why don’t bacteria become resistant to regular soap? It’s a question of how the soap cleans.

“Regular soap is 100% effective at removing pathogens using the effective handwashing techniques we all learned well in 2020,” says Trevor Lithgow, a professor of microbiology at Monash University and director of the Centre to Impact Antimicrobial Resistance.

“In handwashing, soap acts to dissolve the dirt and grime that hold the bacteria and viruses onto your skin, so that they are washed away.”

Unlike antibiotics, soap doesn’t use a molecular process to clean your hands – it uses a physical process. This means that soap doesn’t encourage superbugs: “Because soaps exert a physical action on bacteria and viruses, they do not lead to antimicrobial resistance,” says Lithgow.

Given we’ve been using soap to clean ourselves for millennia without causing the rise of soap-resistant pathogens, this is comforting – but not particularly surprising – information.

Adding antibiotics to soap makes no difference to the way it cleans. “[Antimicrobial] soaps work because they are soaps,” says Lithgow. “In the soap, the additional antimicrobial chemicals provide no further protection beyond what the soap is doing.”

They don’t protect, but they can cause damage – individually, by allowing the bacteria on your hands to become resistant to them, and more broadly by getting into our waterways and encouraging antibiotic resistance there.

Last year, the Australian government released an antimicrobial resistance strategy. Lithgow says that removing antibiotics from soap is key to the strategy’s effectiveness.

“In this national strategy, the federal government has laid out our health and wellbeing over the next 20 years, wherein a key action is antimicrobial stewardship,” he says. “In essence, this means we must discontinue use of antimicrobial chemicals […] where there is no proven benefit to human health.

“In this strategy there is no room for the use of antimicrobials ‘just in case’.”

According to the strategy and to Lithgow, antibiotics must have a “proven need” before they are deployed. That need isn’t obvious in household soap – after all, it’s been effective without antibiotics for centuries.