Exorbitantly high levels of air pollution in Beijing have caused a run on face masks as people look for ways to protect themselves from the smog. Demand is so high that, according to news reports, masks are now in short supply in China’s capital.

But, experts said, a closer look at the kinds of masks people get, the way they wear them and the hazards they’re facing suggests that the masks are unlikely to help much.

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In fact, images of masked citizens navigating the stress of Beijing highlight the false confidence that people put in face masks in all sorts of situations, including flu outbreaks and operating rooms.

“For so long, people have worn these and believed they are effective,” said Lisa Brosseau, a certified industrial hygienist at the University of Illinois at Chicago’s School of Public Health. “But I believe they give people a false sense of protecting themselves when they are really not getting much protection.”

The simplest types of face masks available over the counter are surgical masks, much like the ones that doctors wear while operating on patients.

Surgical masks were designed to protect open wounds from germs in the droplets of mucus that come out of doctors’ mouths when they cough, sneeze and breathe. Masks were never intended to protect the people wearing them, though research shows they may help slow the spread of illnesses, at least a little bit.

In a study published last year in the journal PLOS Pathogens, for example, face masks reduced the amount of influenza virus shed into the air by more than two-thirds.

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That might be enough to lower the chances of giving the flu to others, said study author Donald Milton, a specialist in occupational and environmental medicine at the University of Maryland School of Public Health.

But wearing a surgical mask is not going to eliminate the risk of inhaling unwanted viruses and air pollution. Besides the particles that get through the mask’s filter, surgical masks tend to be loose fitting, allowing contaminated air to flow in around the sides.

Tourists wearing face masks visit Tiananmen Square in heavy smog in Beijing on Feb. 25, 2014. Northern China is braced for more days of hazardous air quality following a week of toxic smog in Beijing that has consistently averaged more than 16 times the World Health Organization's recommended upper limit. Imaginechina/Corbis

In Beijing, where levels of pollution have spiked above 750 micrograms per cubic meter this week, wearing a mask that actually reduced the concentration of inhaled particles by half would still expose people to 10 times more than exposure levels deemed safe by the U.S. Environmental Protection Agency.

Scientists are also still debating whether masks actually protect patients from doctors’ germs. Despite being used by surgeons for decades, masks have been tested in only a few clinical trials, Brosseau said. And results showed that rates of wound infection in patients were the same, whether their doctors wore masks or not.

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For a step up in protection, consumers can buy a category of mask known technically as N95 respirators, which are generally available at hardware stores. These facemasks are often used in industrial workplace situations to protect against things like lead dust and welding fumes, and they are certified by the National Institute for Occupational Safety and Health to trap 95 percent of particles sent through them in testing situations. N99 and N100 masks are also available.

In order to perform to those standards, though, respirators need to be professionally fitted to each person’s individual face to make sure there is a tight seal with no leaks. They don’t work for men with beards. And if they truly fit right, they are uncomfortable to wear.

“If it’s going to work, it has to fit your face,” Milton said. “If you buy a box of these things at the hardware store, it’s not clear you’re getting anything that’s going to work for you.”

Even when masks are fitted correctly, Milton added, studies have shown that they’re very good at trapping relatively large and extremely small particles, but midsize fine particles are the most likely to slip through. Both viruses and components of air pollution fit into that size category. And it’s that size of particle that seems to get stuck in human lungs and cause health problems.

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Overall, experts said, studies suggest that the best way to protect people against pollution and epidemics is not to encourage mask wearing but to address underlying problems, like excessive coal burning or poor health habits.

“We don’t want people to put on these masks and think they don’t need to get vaccinated or wash their hands or do other routine things like cough into their sleeves,” said Pritish Tosh, an infectious diseases physician and researcher at the Mayo Clinic in Rochester, Minn. “If someone chooses to put on a mask, it’s up to them. But it’s important to do other things first.”