You can tell flu season is upon us when you spot people wearing surgical masks in public. You might wonder if they're protecting the public from their sickness or themselves from the public. But can you protect yourself from the flu with a surgical mask?

One 2008 study in the International Journal of Infectious Disease found that when family members of children with flu-like illness wore masks properly, they were 80 percent less likely to come down with the illness.

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"We know surgical masks work because we use them in hospital settings for infection control, so if I'm taking care of a patient with influenza, my hospital requires me to wear a surgical mask when I enter the room," says Dr. Amesh A. Adalja, senior associate at the Center for Health Security and clinical assistant professor in the Department of Emergency Medicine at the University of Pittsburgh Medical Center and School of Medicine.

All that makes sense, but what about wearing a mask out in public?

Adalja says it's going to be protective if you wear it appropriately, and that means you have to wear it all the time during flu season.

The problem, he notes, is that people wear them sometimes and wear them haphazardly or they may not put them on correctly, may wear them too long so the material is worn out, and they don't get the same effectiveness as in the hospital.

Plus, they don't take other precautions like meticulous hand hygiene. "It's not just that you're going to get flu and cold viruses through the nose and mouth; you can also get them on your hands, and at the end of the day you touch your face with the same hand that has the virus on it," says Adalja.

Of course, wearing a mask is not a panacea to prevent the flu.

About 25 percent of people who have influenza don't have symptoms, but they are still contagious. So you might say "I'm worried about getting flu on the subway, but when I go to dinner with my friends, none of them look sick so I'm not going to wear a mask."

That won't work.

While wearing a mask won't hurt — except for the weird looks you garner from strangers — wearing the mask will only be fully effective if you wear it during every interaction with people everywhere all the time, coupled it with excellent hand hygiene, and never touching your face unless your hands are clean.

In other words, you can still get the flu even if you wear a mask. "I would rather advise people to get the flu vaccine; it's much more important to protect yourself from influenza then wearing a mask," says Adalja.