Why does opening windows and going outdoors lower your risk?

You may have heard that outdoor activities reduce the risk of COVID-19 transmission, and that just opening your windows can help. So what is behind these recommendations?

Ventilation is the key to reducing risk indoors. One way we can assess a room’s ventilation is by measuring its “air change rate.” This is the rate at which the air in a room is replaced by air from outside the building. If you run into someone who is contagious while you’re inside, a high air change rate can help carry virus-laden droplets away from you. Unfortunately, many buildings are poorly ventilated.  

Poor ventilation causes respiratory droplets to hang in the air longer and lets  them spread further around  the room. If the droplets come from a person who is contagious, everyone in the room might be exposed. In some cases, people participating in indoor activities like fitness classes have been infected even when participants practiced physical distancing. Opening windows can increase the room’s air change rate and help reduce the risk of spreading the virus.

Of course, ventilation isn’t an issue when you’re outside. Outdoor activities can significantly reduce your exposure should you come into contact with a person who is contagious. But you should still practice physical distancing.  Even outside, the closer you are to a person who is contagious, the more virus you  might be exposed to.

Last update: 12 March, 2021, 09:50 ET

Science review: GHH, ERS