The global body said new information showed they could provide "a barrier for potentially infectious droplets".
Some countries around the world already recommend or mandate the wearing of face coverings in public.
The WHO had previously argued there was not enough evidence to say that healthy people should wear masks.
Dr Maria Van Kerkhove, the WHO's technical lead expert on Covid-19, told Reuters news agency the recommendation was for people to wear a "fabric mask - that is, a non-medical mask".
