People aged over 60 or who have underlying health issues are being advised to wear a medical-grade mask when they are outside and unable to socially distance, according to the World Health Organisation.
The new guidelines announced on Friday are a shift in stance from the organisation, who were previously hesitant to advocate the wearing of face masks in public due to the limited evidence that they offer protection.
In a new guidance document, the health body states medical masks should be worn "in settings where physical distancing cannot be achieved" due to "increased risk of infection and/or negative outcomes".
Those aged under 60 or with no underlying medical conditions should wear a three-layer fabric mask, featuring absorbent cotton close to the face, followed by a polypropylene layer and then a synthetic layer that is fluid-resistant.
These types of masks can be made at home, and there are already numerous brands selling ready-made versions to purchase.
The WHO advises people to wear masks not only on public transport, but wherever physical distancing may be challenging, such as in supermarkets, mass social gatherings and the office, or in closed settings including schools, churches, mosques and other places of worship.
So far the global organisation has not advocated the wearing of face coverings, as there is limited evidence they offer sufficient protection against the virus - and also due to fears that a sudden influx of people buying mask could lead to shortages of medical-grade masks used by health workers.
Informed by research commissioned by the body, it's still unclear to what extent wearers are protected, but the medical-grade design does shield those who use it properly.
It was stressed that wearing a mask is no substitute for physically distancing and regularly washing your hands.
Dr Maria Van Kerkhove, technical lead of Covid-19 response and the head of emerging diseases and zoonosis unit at WHO, said she was worried the wearing of masks offered a false sense of security at protests, such as those taking place in response to the killing of George Floyd in the US.
She said: “There are many gatherings taking place across the globe for different reasons. People who put a homemade mask on feel a sense of protection. It is a false sense of protection.
“Masks must be part of a comprehensive strategy. They do not work alone. They must be used with a number of measures. I want to stress that anyone who is unwell should be at home. They should be tested, their contact should be identified and they should be in quarantine.”
However, WHO director general Dr Tedros Adhanom Ghebreyesus, said the body’s position that masks alone would not protect people had not wavered.
He said: “In the light of evolving evidence, WHO advises that governments should encourage the general public to wear masks where there is widespread transmission and physical distancing is difficult, such as on public transport, in shops or in either confined or crowded environments”.
The new guidance also includes specific washing instructions, with Dr Ghebreyesus adding: "People can potentially infect themselves if they use contaminated hands to adjust a mask or to repeatedly take it off and put it on, without cleaning hands in between.”
In addition, those caring for somebody who is unwell at home should wear a medical, not a fabric mask, according to WHO advice.