The WHO said Monday that asking the general public to wear facemasks could be justified in areas where hand-washing and physical distancing were difficult, but warned masks alone could not stop the coronavirus pandemic.
World Health Organization chief Tedros Adhanom Ghebreyesus also slammed suggestions that Africa should be used as a testing ground for a vaccine as racist.
The global COVID-19 pandemic has killed more than 70,000 people, while more than 1.2 million people have tested positive for the new coronavirus. A vaccine is thought to be at least a year away.
"Countries could consider using masks in communities where other measures such as cleaning hands and physical distancing are harder to achieve because of lack of water or cramped living conditions," Tedros told a virtual briefing in Geneva.
Tedros said he understood that some countries had recommended or were considering the use of both medical and non-medical masks in the general population to prevent the spread of the virus.
However, he stressed that the mass use of medical masks could exacerbate the shortage of protective equipment for healthcare workers, saying some were now facing "real danger".
And he said that outside of health facilities, medical masks were recommended for those who were sick, and their carers.
Tedros also lashed out at "racist" suggestions from some scientists that Africa could be used as a testing ground for a vaccine, which is thought to be 12 to 18 months away.
Two leading French doctors sparked a storm of criticism last week by discussing on television the idea of testing a coronavirus vaccine in Africa, citing its relative lack of resilience to the pandemic in its infrastructure.
They insisted Friday they had been misunderstood and apologised for any offence caused.
Africa has confirmed relatively few cases and deaths so far compared to other continents.
But the WHO and others have long warned that it could be badly exposed should the virus, both in terms of preparedness and health care.