VERIFY: Do masks with valves work?

Описание: The Centers for Disease Control and Prevention recommended the general public wear some kind of face covering or mask several months ago. Since then, more people have searched for and bought a mask.

In some cases, people grab and use whatever they can get including masks that have valves on the outside.


THE QUESTION
Are masks with valves effective in stopping the spread of COVID-19?

THE ANSWER
No. Masks with valves let exhaled particles through without filtration. Some localities have even banned them.


Credit: AP
A British police officer wears a 3M face mask, with few police officers in Britain seen wearing face masks since the outbreak of the coronavirus, outside St Thomas' Hospital, in London, where Prime Minister Boris Johnson remains in intensive care as his coronavirus symptoms persist, Thursday, April 9, 2020. British Prime Minister Boris Johnson remains in intensive care with the coronavirus but is improving and sitting up in bed, a senior government minister said Wednesday, as the U.K. recorded its biggest spike in COVID-19 deaths to date. The new coronavirus causes mild or moderate symptoms for most people, but for some, especially older adults and people with existing health problems, it can cause more severe illness or death. (AP Photo/Kirsty Wigglesworth)

WHAT WE FOUND
A 3M diagram, explaining how its N95 masks with valves work, shows how exhaled air leaves the mask through the valve. The mask is designed for workers requiring respiratory protection in hot and humid environments.

Both the Food and Drug Administration and the CDC note that while N95 masks with valves offer a certain level of protection to the wearer, they should not be used “when sterile conditions are needed.” The CDC explains that’s because “the exhalation valve allows unfiltered exhaled air to escape into the sterile field.”

The valve doesn’t filter the air you exhale, meaning larger droplets you breathe out can escape the mask through the valve. That defeats the purpose of wearing a mask right now -- to prevent people who have the virus from giving it to others.

The CDC says people can spread the virus before they ever show symptoms, meaning that it’s possible a person who feels healthy can spread the virus through particles that may escape out the valve of a mask with one.

Some localities have included these masks when identifying what you shouldn’t wear. One example is in San Francisco, which said, “holes or one-way valves allow droplets out of the mask, putting others nearby at risk.” The Children’s Hospital of Los Angeles also told people not to wear masks with valves when coming into the hospital because they put others at risk.

The CDC still recommends simple cloth face coverings or masks for the general public.