Your plane starts to taxi away from the gate and the open air vents above your seat start blowing out cool air. As you sit back and head up into the sky, do you wonder -- is that recycled air blowing germs down on me? If so, you're not alone.
"I definitely think that airplane air can make me feel sick. I often get a cold after I fly," one woman traveler told "20/20."
"When I get off of the flights I'm normally congested and I have to use my inhalers. And I don't believe airplane air is conditioned the way it should be," a man told us.
But experts say: Don't blame the air up there.
"The air is in fact quite healthy, because of the excellent cabin air filters," said Joe Lundquist, an air filtration expert with Pall Corp. He says state-of-the-art HEPA air filters can capture up to 99.9% of small bacteria and viruses -- even SARS and bird flu virus.
"We've gone through great studies to prove that they effectively remove the bacteria and viruses that people are so concerned about," he said.
Today, HEPA filters are found on most commercial airplanes -- where they re-circulate the air every three to five minutes. A 2002 medical study found that passengers flying in planes with re-circulated air had no more colds than people on planes ventilated with fresh air. So, how did you catch that cold on the plane?
Being on a plane packed with people coughing or sneezing near you is the reason you catch colds. In fact, that air blowing on you from the nozzles above may even help keep you safe from some of those germs being coughed up all around you.