Air purifiers could be helping to spread Covid-19 in confined spaces such as lifts, a leading study has claimed.
The quality of air in small areas without proper ventilation usually requires a purifier to help kill viruses and bacteria - but there is no system proven to remove coronavirus at this time.
Scientists at the University of Nicosia in Cyprus carried out a study to see what would happen if a person coughed in a crowded lift.
Professor Dimitris Drikakis said: 'Our results show that installing an air purifier may increase the droplet spread.'
A 3D model created by scientists shows how air purification systems in lifts may help spread Covid-19 germs released after an infected person coughs
The study claims devices increase the rate of transmission by moving particles laden with the virus.
Air quality in small spaces would quickly diminish without proper ventilation.
So most modern elevators are equipped with air purifiers to remove any floating contaminants.
The machines use ultraviolet radiation to kill viruses and bacteria, which may be harmful.
The model created a lift that would have space to hold roughly five people, with scientists concluding: 'Installing an air purifier may increase the droplet spread.'
Scientists from the University of Nicosia say lifts should operate a lower capacity to minimise the risk of Covid-19 spreading
But sucking dirty air in and blowing clean air out adds to 'overall circulation', a problem which has not been considered until now.
A 3D model of a lift capable of holding five people was created by the researchers.
Ventilation and a purifier were added to the lift so the researchers could determine how they influenced air circulation.
A mild cough was then simulated in space to measure the spread of virus infected saliva droplets.
Using the same model, previous studies have found saliva droplets can travel 18 feet in five seconds when an unmasked person coughs.
The chances of catching the virus were lowest when the space had reduced ventilation, the researchers found.
Prof Drikakis added: 'We quantified the effect of air circulation on airborne virus transmission and showed that installing an air purifier inside an elevator alters the air circulation significantly but does not eliminate airborne transmission.'
People in the UK have been told to stay home since the government declared a national lockdown at the beginning of January.
But for those who are still going into the office or live in an apartment block, taking the lift may be part of their daily routine.
Professor Drikakis said: 'Our results show that installing an air purifier may increase the droplet spread.
Most modern elevators are equipped with air purifiers to remove any floating contaminants. Footage from the study shows how particles move around the 'lift', potentially coming into contact with people on board
The more people inside the elevator are infected with COVID-19, the more damage an air purifier causes, the researchers also found
'The air intake integrated inside the purifier equipment induces flow circulation that can add to the transport of contaminated saliva droplets in the cabin.'
The more people inside the elevator are infected with COVID-19, the more damage an air purifier causes, the researchers also found.
Professor Drikakis added: 'Restricting the number of people allowed in an elevator would minimise the spread of the virus as would better design of air purifier and ventilation systems.'
The findings were published in the journal Physics of Fluids.
Last year a report from Which? warned people that domestic air purifiers were not proven to remove 100 per cent of Covid particles from a room.
The watchdog said their effectiveness depended on factors including the size of the room and the type of filter used by the purifier and its age.