https://www.scientificamerican.com/article/how-to-use-masks-during-the-coronavirus-pandemic/

Any mask worn for day-to-day protection against COVID-19 is going to be imperfect, at least for now. Supplies of N95 respirators—the most effective mask type—should find their way to those in daily close contact with infected people. This requirement leaves the rest of us reusable cloth face coverings and single-use paper surgical masks. (The latter are also in high demand for frontline folks, so if you’re looking to buy, try to acquire fabric masks.)

“These are not going to be perfectly efficient,” says Kirsten Koehler, an occupational and public health expert who studies personal protection at Johns Hopkins University. But they can still help limit the virus’s circulation, especially if they are worn by those infected with the novel coronavirus—many of whom may be asymptomatic. “We’re trying to prevent spreading disease to other people,” Koehler says. “Hopefully the mask is helping to protect us, too.” Even with our faces covered, she adds, we should continue to perform social distancing and isolation. A handful of best practices can help make the most of our imperfect personal protection.