The health body states coronavirus can enter the body through respiratory droplets and contact, but wearing a medical mask "is insufficient to provide an adequate level of protection, and other measures should also be adopted".
It has advised that the masks should be reserved for health care workers, who need them the most.
If you are healthy, you only need to wear a mask if you are taking care of a person with suspected Covid-19 infection, it said.
Prof David Heymann, of the London School of Hygiene and Tropical Medicine, said that unless people were working in healthcare settings, masks are “only for the protection of others, not for the protection of oneself”.
He added masks could create a 'false sense of security' and may end up putting people at greater risk. Even with the mouth and nose fully covered, the virus can still enter through the eyes.
“People think they are protected when they are not,” he said. “Healthcare workers, in addition to the masks, wear visors too, to protect the eyes.”
WHO states that studies have found evidence that the use of a medical mask can be beneficial in preventing the spread of infectious droplets from an infected person to someone else.
The body's new report reads: "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."
WHO adds that you should wear a mask if you are coughing and sneezing.
It also states that masks are effective only when used in combination with frequent hand-cleaning with alcohol-based hand rub or soap and water.
WHO's guidelines state:
If you wear a mask, then you must know how to use it and dispose of it properly.
Before putting on a mask, clean hands with alcohol-based hand rub or soap and water
Place the mask carefully, ensuring it covers the mouth and nose, and tie it securely to minimize any gaps between the face and the mask.
Avoid touching the mask while wearing it.
Remove the mask using the appropriate technique: do not touch the front of the mask but untie it from behind.
After removal or whenever a used mask is inadvertently touched, clean hands using an alcohol-based hand rub or soap and water if hands are visibly dirty.
Replace masks as soon as they become damp with a new clean, dry mask.
Do not re-use single-use masks.
Discard single-use masks after each use and dispose of them immediately upon removal.
Wash your hands frequently
Regularly and thoroughly clean your hands with an alcohol-based hand rub or wash them with soap and water.