Face masks are now recommended for all, but how much do they help?

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This post has been updated.

No one wants to get sick. During pandemics—or even just normal flu season—that desire to avoid the ill and infirm shoots up, and we start taking extra precautions. But if you only do one thing to keep yourself from catching a virus, don’t let it be wearing a face mask.

It’s not so much that face masks are completely ineffective. In theory, they do work to prevent sprays of virus-laden fluid from entering your nose and mouth, and they provide a great reminder not to touch your face, which is a common route of transmission. More importantly, if you’re ill, they help keep those same infected fluids inside your mouth and sinuses, which helps keep other people around you healthy.

But in practice, neither the standard surgical variety nor the heavier duty N95 respirator masks do a whole lot to keep bugs from spreading person-to-person. Even in hospital settings, the few studies on the topic find that the N95 respirators weren’t any better than common surgical masks at preventing the spread of respiratory illnesses.

There haven’t been many more studies about how well those basic masks work, but a 2011 review suggests they probably offer some protection, especially in certain circumstances. The closer your contact with an infected person, the more likely a mask is to work as a physical barrier, for instance. They don’t seem to work that well in operating rooms, where they originated, but some analyses have found that even basic masks can reduce your risk of getting a respiratory illness. Still, other studies have concluded that there’s little evidence wearing one is all that effective in keeping people healthy.

Part of the problem is likely that air can get around the barrier of the mask, but public health experts say perhaps the biggest reason face masks are ineffective is that breathing air with viral droplets simply isn’t how you get sick most of the time.

Certainly some viruses travel well through the air in aerosolized droplets, but you’d need to be in close proximity of a sick person sneezing or coughing for that to happen. On the other hand, you shake hands with a sick person or touch things that a sick person has recently touched quite often, even without realizing it. You also touch your face roughly 52 times every day, and every time you do you carry infectious agents from whatever you just touched to the region around your nose and mouth. From there, those bacteria or viruses can get into your mucous membranes and cause disease.

It’s for this reason that the World Health Organization doesn’t suggest using surgical masks alone as a method of prevention. When used in conjunction with frequent hand-washing—the gold standard of disease prevention—they can be effective. But alone, they won’t do much, though they might do something. And right now, something might be enough to recommend them.

As this pandemic progresses, some people have started arguing that something might be better than nothing. That argument certainly holds weight, and indeed Some states have now made it mandatory to wear some kind of face mask when in public, and the Centers for Disease Control have switched stances to now recommend that people wear cloth masks when out and about. That change hasn’t come from any new data, but rather out of an abundance of caution. In the face of a lot of unknowns about this virus, public health officials are now trying to err on the side of doing too much. It probably won’t hurt for everyone to wear a mask, and it might do something—so we may as well do it, right?

Of course, that’s only true if folks are wearing their own fabric masks, not the surgical variety or N95 respiratory, both of which are in short supply.

Hospitals all across the US and in Europe are facing shortages of even basic face masks, and it’s these healthcare professionals who are most in need of protection. That’s why hospitals have been calling on anyone who has a stash of masks to donate them to their local health care center—we have to protect the people on the front lines first. Folks in close contact with multiple COVID-19 patients will see the most benefit from wearing masks.

The main circumstance in which an average citizen should definitely don one is when you’re ill and need to go somewhere in public, like a doctor’s office or a hospital. Surgical masks do help reduce the number of viral particles you release into the air. But unless you urgently need medical help, people with cold- and flu-like symptoms should not be leaving the house at all.

If you’re healthy and want to wear a mask (or are now required to do so), it’s also crucial to do it properly. Buy disposable masks, not cloth ones—the warm, moist environment near your mouth makes it likely that a more permanent mask will harbor bacteria and viruses, thus increasing your chances of getting sick (though if cloth is all you have and you’re in close contact with someone who’s ill, washing it regularly may still be better than nothing). If you have a fabric mask, make sure you’re washing it after each use. You’ll need to wear the mask all the time, since you never know when you might be around an ill person, and you’ll have to make sure you don’t keep touching your face to adjust the mask—that would be wildly counterproductive. When you remove it at the end of the day, make sure not to touch the front, which may be contaminated with viral cells. Remove it by the ear straps. Otherwise you’re just transmitting everything the mask has been filtering out all day onto your hands, which will likely touch your face several times in the next hour. Again—counterproductive.

By far your best bet to keep from getting sick isn’t to wear a mask at all—it’s to avoid touching your face and to wash your hands frequently. It’s the last thing many of us want to do when our skin is already parched and cracking, but prevention is the best medicine. Though people have been buying up stocks of hand sanitizer, which is effective against the coronavirus, regular old hand soap is actually better—the soap itself kills the virus. So get thee a solid hand cream and wash those digits, for everyone’s sake.

Update: A version of this article was originally published in February. It has been updated.