Depending on where you live, you might be seeing masked joggers and cyclists on the streets of your neighborhood. Or you might have gone for a run yourself, mask-free, and been heckled to mask up. At this point, most thoughtful people wear masks indoors in public and outdoors in crowded situations, but wearing a mask when you’re outdoors and alone — or far away from anyone else — has become a frontier of intense debate.

U.S. presidential candidate Joe Biden added to the confusion when he recently called for a national mask mandate. In no uncertain terms, he said it could save 40,000 lives over the next three months if everyone wore a mask “outside.”

But that’s not what the experts say. For one thing, there’s overwhelming evidence that the virus is being transmitted primarily indoors. That’s why director of the National Institute of Allergy and Infectious Diseases Tony Fauci has said he and his wife pull their masks down to their chins when they jog outside — he only pulls it back over his nose and mouth if he has to pass someone.

The Biden-Fauci discrepancy raises an interesting question about risk communication: Is it better to give simple guidance even if it means being more draconian? Or is it best to be more precise — following the best scientific evidence to date about high-risk activities and lower-risk ones? In the case of masks, that amounts to masking indoors in public places and outdoors only when you can’t stay 2 meters away from others. (Rhode Island has such a policy, which came in for high praise from Fauci in the same interview.)

Biden might have been trying to go with simple and draconian. It certainly doesn’t hurt to wear our masks all the time, even if it goes beyond what America’s most famous infectious disease expert advises. But if this is what Biden is trying to achieve, he needs help with clarity.

Risk communication consultant Peter Sandman says he was puzzled by Biden’s statements. “Did he misspeak, saying ‘outdoors’ when he meant ‘indoors’? Did he misunderstand the briefings he has been getting from experts, who surely told him transmission is at least an order of magnitude likelier indoors than outdoors?”

The latest evidence about aerosol transmission points to indoor environments being the primary risk. The aerosol particles that carry the virus hang around longer indoors and disperse very quickly outdoors. “In terms of actual prevention of transmission, the biggest bang for your buck is when you’re going to be close to people and when you’re in an indoor setting,” says Harvard epidemiologist Julia Marcus.

That would explain a number of contact tracing studies done mostly in Asia and Europe, which show that most people who get infected don’t transmit the disease to anyone, but a few transmit it to many in so-called superspreading events. These happen primarily indoors — not at the beach, or among people taking walks outdoors.

Emphasizing universal outdoor mask-wearing is not good risk communication, says Sandman. How much masks help and in what circumstances is still under some degree of debate. Over the long haul, exaggerating the benefits of mask-wearing could undermine credibility.

Harvard professor and infectious disease specialist Michael Klompas says the evidence for the benefits of masks come from a variety of extrapolations — a case study of a hair salon where confirmed infections weren’t passed on; studies of mask use inside hospitals; studies of the mechanics of droplets being blocked; even a study involving hamsters.

But he agreed the benefit is greatest where the risk is substantial — situations where people are in close proximity for some extended duration or indoors. The 40,000 lives Biden referred to might have come from this estimate for the effects of requiring masks for public-facing workers, not people out walking the dog or having a picnic.

It’s possible that making people mask up 24/7 would simplify the rule. There’s evidence that for businesses such as restaurants, simple safety rules are more likely to be followed than complex ones.

But Marcus says taking that approach to public health could backfire. “I understand the instinct to keep things simple, but I think we actually do the public a disservice when we assume people can’t handle nuance … people are not stupid,” she says. “People know there isn’t a benefit to wearing a mask when you’re alone in a park or even having a picnic with your family in a park where other families are having picnics and they are all sitting 15 feet away … I think when we are overly heavy-handed in our public health recommendations and go beyond what is actually necessary and evidence-based that’s when we start to lose trust.”

The issue of mask-wearing outside has become politicized because it’s so visible. “We focus on what’s visible and we focus on what makes us angry,” says Marcus. “I think (seeing) people enjoying themselves tends to spark moral outrage.”

Shame-based, overly extreme public health recommendations have backfired in other areas.

Marcus studied HIV prevention before this new pandemic arose. Safer sex proved more sustainable than total abstinence, she says. “We see when you give people more nuanced information on risk and choices on safer alternatives to high-risk behaviors, rather than just condemning them, you actually have better health outcomes.”

An even more elemental level of human contact is now at stake. To get through this we’ll need the same thoughtful, science-based, compassionate approach that public health experts deployed to get us through the AIDS crisis. Fauci has it right. And while he may have his enemies, there’s no doubt he’s broadly credible and wildly popular. Biden could do worse than follow his lead.

Faye Flam is a Bloomberg Opinion columnist. She has written for The Economist, The New York Times, The Washington Post, Psychology Today, Science and other publications. She has a degree in geophysics from the California Institute of Technology.

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