People should wear masks to prevent the spread of COVID-19, but not those with exhalation valves or vents, the Centers for Disease Control and Prevention says.
Masks with these one-way valves are intended for use in construction work, allowing users to breathe in filtered air and exhale warm, moist air through the valve, according to The Washington Post. These valves reduce heat and moisture inside masks, making them more comfortable to wear for long periods.
But this design doesn't prevent the spread of infectious diseases. The main reason for wearing masks in the COVID-19 era is to prevent respiratory droplets from traveling into the air when a person coughs, sneezes or talks, the CDC says. But when a mask has a valve, respiratory droplets from the wearer are expelled into the air and could reach other people.
"This type of mask does not prevent the person wearing the mask from transmitting COVID-19 to others," the CDC says on its website.
Many airlines have already banned customers from wearing masks with valves on flights, the Post reported. American Airlines is the latest airline to announce a ban, which takes effect on Aug. 19, according to a statement from the airline issued Wednesday (Aug. 12).
The CDC does recommend wearing cloth masks when in public, and notes that surgical and N95 masks should be reserved for health care workers and first responders.
Originally published on Live Science.