Science has a lot to say about the effectiveness of wearing a mask to stop Covid-19, but the communication of that science has been corrupted by:

Partisan divides
Sensationalist media stories
Distrust
False dichotomies https://trib.al/xzMKmkv 

The studies on masks aren’t perfect, but that’s typical of many issues involving health risks — from mercury contamination to cancer screenings.

It’s still better to make decisions based on an incomplete body of evidence than to ignore evidence altogether https://trib.al/xzMKmkv 

A consensus is finally starting to form that there’s a negligible risk outdoors away from other people, and that very brief encounters pose very little risk, such as:

Walking
Running
Cycling
https://trib.al/xzMKmkv 

Common sense would suggest that if an activity poses negligible risk, then wearing a mask offers only a negligible benefit, and should be optional https://trib.al/xzMKmkv 

On the other extreme are potential super-spreading events — anywhere many people are confined indoors, especially if there’s close contact.

Trump’s rally is a good example. There, common sense would dictate that such events should not take place at all https://trib.al/xzMKmkv 

Mask wearing is likely to do the most good in settings where people have little choice but to interact in enclosed spaces:

Grocery shopping
Riding public transportation
Ride-sharing
Getting a haircut
Seeing a doctor
https://trib.al/xzMKmkv 

Also in this middle category is gathering outdoors in large groups — such as at a protest.

If most protestors wear a mask at all times, this will likely reduce transmissions https://trib.al/xzMKmkv 

And length of exposure matters a lot, so these professionals face a much higher risk than their customers:

Bus drivers
Haircutters
Store clerks

Their risk very likely goes down if customers wear masks https://trib.al/xzMKmkv 

Then there’s a problematic category of activities, such as eating in restaurants, where masks can’t be worn constantly.

Some experts say such “fiddling” with masks is only going to spread any viruses the mask has captured https://trib.al/xzMKmkv 

The risks associated with close contact and crowds seem obvious and intuitive.

And yet Americans have been fixated on the unlikely possibility that infectious doses of virus would fly off cyclists or creep in on packages https://trib.al/xzMKmkv 

Some people have adopted irrational mask-wearing practices, such as keeping one on while riding or driving, but pulling it down to congregate and chat with groups of people https://trib.al/xzMKmkv 

And it’s no surprise that politics would infuse the issue. In the U.S., we have some fraction of people wearing a mask all the time, and some fraction never wearing one.

It would be better if everyone wore one when it was likely to help https://trib.al/xzMKmkv