Some people have taken to yelling (online and off) at people exercising without masks.

“If you are yelling at someone to wear a mask, then give them a mask,” she said.

Several months into the coronavirus pandemic, battles over when to wear masks have heated up, sometimes with political alliances replacing health guidelines.

When cities and states started urging people to wear masks to reduce transmission of the coronavirus, some made exceptions for exercising.

Carry a mask, many seemed to say, but if you’re by yourself on an empty street, you don’t have to wear it.

Likewise, San Francisco has urged runners to carry a mask and put it on when they are near other people.

The Centers for Disease Control and Prevention recommends wearing cloth face coverings in public settings “where other social distancing measures are difficult to maintain,” but offers no specific guidance on exercising.

“It’s harder to breathe, and it’s a lot more clammy,” said Gaston Ly, a store manager at Running Room in Honolulu.

(In Kentucky, Gov. Andy Beshear asked residents to begin wearing masks in public on May 11. Like officials elsewhere, he made an exception for people exercising alone.).

Even in Hong Kong, a city so committed to face coverings in public that it has been widely praised as a model, there is little expectation that runners will wear masks, said Brian Woo, a founder of a running group there.

“I assume it’s just understood that running is not a time for wearing masks,” he said.

There is no scientific consensus around the importance of wearing a mask while exercising, primarily because so little relevant research has been completed.

They also agree that it’s best to avoid exercising within six feet of anyone beyond your immediate household and that working out is less risky outside than inside.

“Outdoors is relatively safe, and masks would only be important if you are exercising in crowded areas or indoors in space shared with other people,” he said.

Even if you aren’t being told to stay at home, it’s still a good idea to limit trips outside and your interaction with other people.

The best way to protect yourself from coronavirus — whether it’s surface transmission or close human contact — is still social distancing, washing your hands, not touching your face and wearing masks.

Most people fall ill five to seven days after exposure, but symptoms may appear in as few as two days or as many as 14 days.

There is an uptick in people reporting symptoms of chilblains, which are painful red or purple lesions that typically appear in the winter on fingers or toes.

Yes, but make sure you keep six feet of distance between you and people who don’t live in your home.

has recommended that all Americans wear cloth masks if they go out in public.

This is a shift in federal guidance reflecting new concerns that the coronavirus is being spread by infected people who have no symptoms.

Until now, the C.D.C., like the W.H.O., has advised that ordinary people don’t need to wear masks unless they are sick and coughing.

One useful takeaway, both the study’s authors and several researchers not involved in it said: It’s best to avoid running or biking directly behind someone for a prolonged period.

He advises taking a mask, even if you don’t expect to cross paths with anyone.

“Over time, you’ll get used to it,” said Joey Ta, a competitive endurance athlete in Los Angeles who recently started wearing a mask.

People exercising have used several kinds of masks, some with drawbacks.

And whether you wear a mask or not, pay attention to the position of people around you.

“I don’t understand how people can’t understand that this is about more than just a mask,” said Ms