If people are wearing masks for extended periods of time without properly cleaning them, Furness said, a bacterial biofilm can build up on the outside layer of your mask.
“If 30 million people are wearing a cloth mask all day long, you’ll see a noticeable spike in bacterial lung infections in a month or so,” he said. “Especially because many people wearing them are often immunocompromised.
“Think about it: our bodies are not designed to have a dirty cloth in front of our mouth all day.”
Furness said you should still wash your mask in your washing machine after each use. He also recommends boiling it once in a while to kill bacteria.
The big risk with face masks is self-contamination — that is, if you adjust your mask with dirty hands.
The experts with whom we spoke said good hand hygiene and not touching your face is key when wearing masks, especially when taking them on and off.