Masks have become a new part of everyday life for Americans this year. And with anything that is new, there is bound to be some confusion. For instance, many people may be unsure of when masks are completely necessary and which situations you can forgo a mask in–which can lead to many mistakes. In fact, Anthony Fauci, MD, director of the National Institute of Allergy and Infectious Diseases (NIAID), says that many people are still making this mask mistake: taking their mask off to talk to someone who can't hear or understand them.During an interview with Trevor Noah on the Sept. 21 episode of The Daily Show, Noah asked the health expert if it was necessary to wear a mask during a series of different scenarios. And when it came to talking to someone who couldn't hear you, Fauci said keeping your mask on was vital. Instead of taking your mask off, you should just "say it again and repeat it" until they can hear you, he said."Because when you then put down [your mask], you tend to speak louder with more force, and that's when all of the particles—if they're there, if you're infected—will come out," Fauci explained. "I would leave the mask on."After all, there's research that shows talking can easily spread the coronavirus. One study, published on May 13 in the Proceedings of the National Academy of Sciences of the United States of America, found that speaking in a loud voice could introduce thousands of fluid droplets containing viral material into the air every second, droplets that could still be detected in the air for up to 14 minutes in an environment with stagnant air.There were other scenarios where Fauci said a mask was necessary, even if people don't think so. Some of the examples he gave were wearing a mask between courses when dining out and when in an empty elevator, as people can quickly come in.RELATED: For more up-to-date information, sign up for our daily newsletter.However, there may be some instances when you may not have to wear a mask, according to Fauci. For instance, if you're riding your bike out on the street, he says you don't have to wear a mask if you're not near other people. He did note that you should have your mask on you "in case you come into close contact with people on the outside."If you're indoors, however, Fauci said you should keep your mask on, no matter how socially distanced you are from other people—even if someone you're talking to asks you to speak up. And for more guidance from the nation's leading infectious disease expert, Dr. Fauci Says You Shouldn't Go Here Until a Year After a Vaccine.