When it’s humid outside, it could feel like it’s harder to breathe if you’re not used to wearing a mask, said Benjamin Neuman, a professor of biology at Texas A&M University-Texarkana. But he said masks don’t meaningfully decrease oxygen in the body.
“The body is quite good at adjusting to keep oxygen levels where they need to be,” he said.
There’s also no evidence that the use of masks causes fungal or bacterial infections, according to Davidson Hamer, an infectious disease expert at Boston University. Disposable face masks are meant to be used once, then thrown in the garbage. With cloth masks, it’s a good idea to wash them regularly.