The World Health Organization (WHO) has warned against using homemade masks while out in public, saying there's no evidence they'll stop you catching COVID-19.
Nor might most medical-grade masks for that matter, the WHO says in its latest advice, because they can create a "false sense of security, with neglect of other essential measures, such as hand hygiene practices and physical distancing".
"There is good evidence that wearing a medical mask is beneficial when you are a healthcare professional and in close contact with people who have COVID-19," said Mary-Louise McLaws, a researcher at the University of New South Wales and a member of the WHO's COVID-19 expert advisory panel on COVID-19.
"However, there is no evidence that healthy people wearing masks out in the community generally are protected from COVID-19."
The disease, caused by the SARS-CoV-2 virus, has killed nearly 100,000 people and infected more than 1.5 million over the past couple of months.
Regularly seen in Asian countries since the SARS outbreak of 2003, facemasks have become commonplace in public in New Zealand and other Western countries. The virus is widely believed to be spread via droplets expelled in coughs and sneezes, but there have been recorded cases of transmission from patients who aren't showing symptoms like these.
While homemade masks may stop droplets, Prof McLaws says they're not as effective as surgical-grade masks, especially those which form a seal around the nose and mouth.
"The production of masks is complex, for example some masks are made up of polypropylene central layers that are charged to prevent penetration of particles and designed to fit the face to provide a seal to prevent small particles from entering the mask.
"Both N95 and surgical masks are lab tested to ensure they filter at least 95-98 percent of lab particles.
"It is understandable that people in places like New York City where the COVID-19 infection rate is very high are nervous and may resort to making their own masks. While a mask made out of cotton may provide a small amount of protection from droplets, it is incredibly important that this does not give people a false sense of security."
A Hawke's Bay artist earlier this week made headlines after making and selling masks made of flax, despite expert opinion they wouldn't work.
The WHO points to a 2015 study published in journal BMJ Open which found healthcare workers who used cotton cloth masks were actually "at increased risk of infection compared with those who wore medical masks". Cloth masks retain moisture, aiding the virus' survival.
What if I have to wear a mask?
Health experts say if you have to go out in public, social distancing, washing your hands and avoiding touching the face are the most effective ways to avoid being infected. Wearing a mask "may lead to touching the face under the masks and under the eyes", the WHO says.
Those with symptoms of COVID-19 should wear a mask though, the WHO says, as should those caring for them if they're self-isolating at home.
"There is limited evidence that wearing a medical mask by healthy individuals in the households or among contacts of a sick patient, or among attendees of mass gatherings may be beneficial as a preventive measure. However, there is currently no evidence that wearing a mask (whether medical or other types) by healthy persons in the wider community setting, including universal community masking, can prevent them from infection with respiratory viruses, including COVID-19."
Mass gatherings in New Zealand are currently banned.
If you do insist on wearing a mask, the WHO says you should be careful not to touch it with your hands, and if you do, dispose of it and wash your hands. Don't reuse single-use masks.
