People spending a penny in public toilets should always wear a face mask to reduce the risk of being infected by Covid-19, warns a new study.
Chinese scientists found that flushing public urinals can release clouds of virus-laden aerosols within five seconds, while normal toilets can infect within 35 seconds of being flushed.
The researchers from Yangzhou University in China simulated and tracked virus-laden particle movements when urinals are flushed.
Their findings, published in the journal Physics of Fluids, clearly show public toilets can be "dangerous" places for potentially becoming infected from a virus, especially during the COVID-19 pandemic.
Other research has shown that both faeces- and urine-based virus transmission is possible.
Researcher Dr Xiangdong Liu said: "We used a method of computational fluid dynamics to model the particle movement that occurs with the act of flushing. The specific models are the volume of fluids model and discrete phase model."
Dr Liu explained that flushing a urinal, much like flushing a toilet, involves an interaction between gas and liquid interfaces.
The result of the flushing causes a large spread of aerosol particles to be released from the urinal, which the Chinese team simulated and tracked.
Dr Liu described what the simulations revealed as "disturbing."
The trajectory of the tiny particles ejected by flushing a urinal "manifests an external spread type, with more than 57 per cent of the particles travelling away from the urinal," said Dr Liu.
But that's not all. When men use urinals within a public toilet, the tiny particles can reach their thigh within 5.5 seconds when compared to the toilet flush, which takes 35 seconds to reach slightly higher.
But Dr Liu explained that that particles from urinals, "show a more violent climbing tendency."
De Liu added: "The climbing speed is much faster than toilet flushing."
Urinals are used more frequently within densely populated areas, and the researchers warned that particles will travel faster and farther, posing a "serious public health challenge."
The team said their findings underline how important it is to wear a mask within public places, but especially in public conveniences.
Dr Liu added: "From our work, it can be inferred that urinal flushing indeed promotes the spread of bacteria and viruses.
"Wearing a mask should be mandatory within public restrooms during the pandemic, and anti-diffusion improvements are urgently needed to prevent the spread of Covid-19."
