American CDC updated its mask guidelines
The US Centers for Disease Control and Prevention has changed its mask guidelines to recommend that people "wear the most protective mask you can that fits well and that you will wear consistently."
The agency describes well-fitting respirators approved by the National Institute of Occupational Safety & Health (NIOSH) -- such as N95 masks -- as offering "the highest level of protection.", CNN reports.
The updated guidelines come after many public health experts have been recommending for months that people wear more effective masks -- particularly N95s -- and that the CDC change its guidelines on mask-wearing.
KN95s and KF94s
These masks and their international counterparts known as KN95s and KF94s are often made of multiple layers of polypropylene, a synthetic fiber. They are designed to achieve a very snug facial fit, with straps that go around the back of the head and edges that form a tight seal around the nose and mouth.
N95 respirators worn correctly are designed to filter out at least 95% of particulate matter in the air, preventing anything larger than .3 microns from passing through.
KN95s and KF94s are certified in China and South Korea, respectively, and offer similar protection to N95 masks. KF stands for "Korean filter" and indicates 94% filtration.
The best masks are some version of N95," said Eric Toner, senior scientist of environmental health and engineering at Bloomberg School of Public Health, Johns Hopkins University. "N95s, KN95s and KF94s are functionally equivalent."
Masks with an exhaust valve do not prevent the spread of the virus to other people.