People in Wales are being advised by the Welsh Government to wear non-medical face masks on public transport and in other places where social distancing is difficult.
Health Minister Vaughan Gething said that people were not being recommended to wear the face coverings outdoors.
And he said that people with symptoms should not think it was safe to go out with a mask and should instead remain at home and self-isolate for seven days..
Mr Gething told Tuesday's press conference that people who are symptomatic "must self-isolate for seven days and get a test", as set out in existing guidance.
The Welsh Government has also published the technical advice on which it based its decision to change the guidelines.
In a statement, Mr Gething said: "Washing your hands, avoiding touching your face and maintaining a tw-metre distance from others remain the best way of stopping the spread of the virus.
"On Friday, the WHO updated their guidance on face coverings, advising that they should be considered in settings where maintaining social distancing is difficult.
"However, to be crystal clear, wearing a face covering does not replace the need for social distancing or washing your hands regularly.
“Further scientific evidence is needed on the benefits to the wider public of wearing face coverings, but observational findings so far suggest that homemade or purchased three-layer face-coverings might reduce transmission from one person to another if made, worn, handled and disposed of properly.
"Therefore, on balance, we are recommending to the people of Wales that three-layer face-coverings should be used in situations where social distancing measures can be more difficult to achieve, for example, on public transport. We are not recommending their use outdoors.
"The wearing of face coverings will not be mandatory, but we will encourage people to do this for the benefit of themselves and others.”
The decision follows the announcement that face coverings would be required on public transport in England from June 15.
In England, travellers can be fined or refused permission to board buses or trains if they refuse to comply with the order.
The Welsh Government initially said it was considering similar decision as public transport regularly crosses between both countries - sometimes more than once on a single journey.
Speaking about the issue at a Welsh Government coronavirus briefing last week, the First Minister hit out at the UK Government for its lack of communication.
Mr Drakeford said the Welsh Government received no advance notice from the Department for Transport in England that an announcement on face masks was going to be made.
He said: "I wish we would have had chance to explore this with the UK Government before they made an announcement."
