WHO also said that, where possible, gatherings should be held outdoors.
The World Health Organisation (WHO) has urged families to wear face masks during Christmas gatherings this year.
WHO said celebrations should be held outdoors if possible, and that "participants should wear masks and maintain physical distancing".
The latest guidance said that leaving doors open to ensure good ventilation is also a safety measure worth taking.
WHO said: "Indoor gatherings, even smaller ones, can be especially risky because they bring together groups of people, young and old, from different households, who may not all be adhering to the same infection prevention measures.
"Gatherings should be held outside if possible, and participants should wear masks and maintain physical distancing. If held indoors, limiting group size and ensuring good ventilation to reduce exposure risk are key.
"It may feel awkward to wear masks and practise physical distancing when around friends and family, but doing so contributes significantly to ensuring that everyone remains safe and healthy."
This comes as WHO said that there is a "high risk" of further resurgence of cases across Europe in the first weeks and months of 2021, and that we all must do our bit to stop it.
Immunologist Professor Luke O'Neill has previously urged people not to "pass the gravy boat" to each other while eating Christmas dinner this year,
in an attempt to stop the spread of Covid.
