As more Americans are vaccinated against the coronavirus and a growing body of scientific evidence suggests that the risk of outdoor transmission is low, many people are wondering: Do we need to keep wearing face masks outside?

The short answer is that masking outdoors can be “optional,” says Paul Sax, clinical director of the Division of Infectious Diseases at Brigham and Women’s Hospital in Boston. While Sax says people should don masks indoors in public and around large crowds, he and other experts believe statewide mandates for wearing masks outdoors all the time may no longer be necessary. (Update: The Centers for Disease and Control and Prevention has echoed this view in its latest guidance on mask wearing for vaccinated individuals.) “The science of the viral transmission is advanced enough that we really don’t want to be kind of confusing people by forcing them to wear masks in places where really they’re at minimal risk,” he says.

But before you start spending all your time outdoors barefaced, experts emphasize that decisions about when to wear a mask outside largely depend on personal risk assessments involving a variety of virus-related factors. What is your vaccination status? How many other people could you be interacting with? Do you know their vaccination status? How much prolonged close contact could you have with them? Are you, or is anyone in your household, at increased risk for becoming severely ill from covid-19?

“There is not necessarily a straightforward rule,” says Krystal Pollitt, an assistant professor of epidemiology at the Yale School of Public Health. “A lot of it really comes down to still thinking of the level of risk of the situation around you and the people around you, especially.”

Here’s how experts say you should assess risk and what they recommend about masking in various outdoor scenarios.