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Coughs are one of the key ways for Covid-19 to spread – so, keeping them to ourselves is a pretty important way to prevent the virus from doing the rounds. Especially come winter when we’re all indoors.
A new study has analysed the different methods people use to cover coughs – from cupping a hand over the mouth to spluttering into the crook of your elbow, as well as wearing face covers.
Researchers in India visualised the flow fields of coughs under common mouth-covering scenarios and determined which ones were best for keeping those droplets to a minimum (because let’s face it, nobody wants to be sprayed by another person’s cough).
Coughs tend to be warmer than their surrounding area, so study author Padmanabha Prasanna Simha, from the Indian Space Research Organisation teamed up with Prasanna Simha Mohan Rao, from the Sri Jayadeva Institute of Cardiovascular Sciences and Research, to use a technique called schlieren imaging and capture pictures of voluntary coughs from five test subjects.
By tracking the motion of a cough over successive images, the team estimated velocity and spread of the expelled droplets.
The researchers analysed the expelled droplets from an uncovered cough as well as a cough while wearing a surgical mask, wearing a N95 mask, putting a single hand over the mouth, cupping two hands over the mouth, covering the mouth with a folded handkerchief, as well as wearing a surgical mask and bringing a hand to cover the mouth area at the same time. They also looked at the effect of covering a cough with an uncovered elbow and sleeved elbow.
Unsurprisingly, N95 masks were found to be the most effective at reducing the spread of a cough. They reduced a cough’s initial velocity massively and limited its spread to between 0.1 and 0.25 metres. An uncovered cough, in contrast, can travel up to three metres. Even a simple disposable mask can bring this all this down to 0.5 metres, the study found.
People are often told to catch a cough in the crook of their elbow if they’re caught off guard. But if your arms are bare, this isn’t the best advice.
Researchers found that unless the arm was covered by a sleeve, it could not form the proper seal against the nose necessary to obstruct airflow. A cough could then leak through any openings and project in many directions, they said.
Coughing into a sleeved elbow is better, as if the arm is covered by a sleeve, it can act as an obstruction to the nose airflow and the spread into the environment is limited.
What about your hands? Well, covering the nose and mouth with a single hand helped to reduce airflow velocity, but there was “significant leakage” through the gaps between the fingers, with some flow redirected upwards and downwards.
When using two cupped hands to cover the nose and mouth, there were three leaks – through the gap between the palms, airflow redirected upwards and a third leak that passed through the gap left between the fourth and fifth fingers while cupping.
A folded handkerchief held by a hand and an elbow covered by a sleeve are the best options for attenuating the airflow from a cough if N95 masks are not available, researchers said. “If we can prevent clouds of such particles from traveling very far, it’s better than not doing anything,” said Simha. “In situations where sophisticated masks are not available, any mask is better than no mask at all for the general public in slowing the spread of infection.”
Simha and Rao also emphasise masks must be used in conjunction with social distancing. That means keeping a minimum of 1m apart from others. “Adequate distancing is something that must not be ignored, since masks are not foolproof,” Simha said.
Behavioural scientists at Warwick Business School recently suggested wearing face masks can adversely affect attitudes towards social distancing – as people feel more comfortable sitting or standing closer to others while wearing a mask.
Ashley Luckman, a research fellow at Warwick Business School and lead author of the pre-print study, said: “Our findings appear to be a classic case of risk compensation. Wearing masks brings down the overall risk of spreading Covid-19, so people feel safer and are more willing to take other risks, such as decreasing the physical distance between them and others.
“If the government’s aim is to minimise transmission of the virus, its guidelines must be clear enough to prevent this trade-off, emphasising that masks are not an alternative to social distancing.”
Experts are still learning about Covid-19. The information in this story is what was known or available at the time of publication, but guidance could change as scientists discover more about the virus. To keep up to date with health advice and cases in your area, visit gov.uk/coronavirus and nhs.uk.