evidence: "You can really see the mask is doing something," said one of the study’s co-authors, Warren S. Warren, a professor of physics, chemistry, radiology and biomedical engineering at Duke. "There’s a lot of controversy and people say, ‘Well, masks don’t do anything.’ Well, the answer is some don’t, but most do." [...] "Buff performance head and neckwear are not intended to be used as medical-grade face masks or as a replacement for N95 respirators as effective measures to prevent disease, illness, or the spread of viruses," the statement said. [...] The CDC recently updated its guidelines on masks, noting that the agency does not recommend the use of coverings that have valves or vents. "This type of mask does not prevent the person wearing the mask from transmitting COVID-19 to others," the CDC wrote.