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Good news: It looks like we’ve finally made it through this nasty flu season. Hopefully, thanks to a flu shot and lots of hand-washing, you managed to avoid getting sick.

Maybe you even went the extra mile this year and put on a surgical mask to ward off germs in crowded, public places. After all, according to public wisdom, that totally works, right? Well, it’s not that simple.

That fetching paper mask might not have actually prevented you from catching the flu -- but if nothing else, if you were sick, it probably stopped you from infecting everyone else. At first glance, those masks might seem really effective -- even according to some research. In one 2009 study, almost 450 nurses in Ontario, Canada, were assigned to wear either a simple surgical mask or an N95 respirator.

These are specially designed masks that mold closely to the face and block at least 95% of tiny particles. That study, published in JAMA, found that about 23% of nurses ended up catching the flu regardless of the form of protection they used. So case closed, right?

Masks must work at least as well as those fancy respirators at keeping people flu-free. Except… that’s probably not the case. See, there’s a difference between getting sick and being exposed to flu virus.

And other studies have shown that surgical masks are definitely worse at keeping out viruses. One of those studies, published in American Journal of Infection Control in 2006, used samples of a harmless virus to test how good respirators and surgical masks are at protecting their wearers from airborne pathogens. They found that 20 to 85% of the simulated pathogens penetrated the surgical masks, compared to only around 5% for the respirators.

Which is quite the difference. So even if both groups of nurses in that first study got sick just as often, the ones wearing surgical masks were probably exposed to a lot more particles. If you think about it, though, that really isn’t that surprising.

Because here’s the thing: Surgical masks aren’t actually designed to protect you from dangerous particles in the environment. Only respirators are. Instead, the masks intended for the opposite job -- protecting other people from your germs.

See, while respirators fit tightly to your face, surgical masks often have gaps on the sides. They still do a good job covering your mouth and nose, but outside particles can probably sneak in around the mask. So even if they do happen to keep you healthy, that’s not their main purpose.

Still, when it comes to containing your germs, they’re definitely effective. For a 2013 study published in the journal PLOS Pathogens, scientists collected examples of exhaled particles from about 40 flu patients with and without surgical masks. They found that the masks significantly reduced the amount of aerosolized virus that their subjects put into the air.

And a 2009 study from the journal Clinical Infectious Diseases found that surgical masks were just as effective as fancy respirators at keeping the illness from spreading. This is why doctor’s offices will ask patients who are coughing or sneezing to put on a mask while they’re in the waiting room -- to protect everyone else. According to a Mayo Clinic expert, if you’re not sick yourself, just worried about catching the flu, wearing a paper mask might help, and it certainly won’t hurt.

But your best bet is still to suck it up and go get that flu shot. Thanks for watching this episode of SciShow! And special thanks to Lorraine on Patreon for asking, and to all our patrons who voted to have this question answered!

If you’d like to submit a question or vote on the next ones we answer, you can go to patreon.com/scishow. [ ♪ Outro ].