Before traveling to China, we had learned of the air pollution and that most travelers would get sick while in China. This product was hugely successful as 98 percent of all illnesses are air born. So, with our nasal screens ,we spent 18 days in China. One of our group felt “smothered” when she wore the nasal guards and did not wear her’s but one day. She was the only one who became very ill before we left China and for a week at home. None of the rest of us even caught a cold!!! This was 2 years ago, and I still purchase these for air travel, flu season, etc. They work very well in filtering out what needs filtering!!