Saliva can travel over 5.5m in 5 seconds even in a light breeze, study finds

A light wind is enough to send coughed-out saliva over five metres in five seconds, a new study has found.

The research – published in Physics of Fluids today – appears to show that the two-metre social distancing rule in place across much of the world due to COVID-19 could be insufficient to prevent transmission in some circumstances.

Talib Dbouk and Dimitris Drikakis’s study revealed that, even with a slight breeze of 4 km/h, saliva can travel 5.5 metres in five seconds.

"The droplet cloud will affect both adults and children of different heights," Drikakis said.

"Shorter adults and children could be at higher risk if they are located within the trajectory of the traveling saliva droplets."

The research emphasizes that saliva is a complex substance.

Many factors affect how it travels in the air, including the size and number of droplets, how they interact with each other and the air, and humidity.

The team stressed that more studies are necessary to determine the effect of ground surface temperature on the behaviour of saliva in the air.

They also said a study is necessary to examine how saliva behaves indoors, where air conditioning has a large effect.

"This work is vital, because it concerns health and safety distance guidelines, advances the understanding of spreading and transmission of airborne diseases, and helps form precautionary measures based on scientific results," said Drikakis.