The researchers found that wearing one mask — surgical or cloth — blocked around 40% of the particles coming toward the head that was breathing in. When a cloth mask was worn on top of a surgical mask, about 80% were blocked. The study had many limitations: The researchers used one brand of surgical mask and one kind of cloth mask, and it's not clear if results would be the same with every product. AdTwo months later, after it became clear that infected people who did not exhibit symptoms could spread the virus, the CDC began recommending people wear masks in public. A recent University of California survey suggested that only about half of U.S. adults wear masks when in close contact with people outside their household.