JAbanese researchers have shown that masks can provide protection from airborne coronavirus particles, but even professional-grade hoods cannot completely eliminate infection risks.

Scientists at the University of Tokyo built a safe room with mannequin heads facing each other. One head is fitted with an inhaler that mimics a cough and flushes out actual coronavirus particles. The other simulates normal breathing, with a collection room for viruses entering the airway.

The cotton mask reduced viral absorption by the recipient head by up to 40 percent compared to no mask. The N95 mask, used by doctors, has prevented up to 90 percent. However, even when the N95 was attached to the face with duct tape, some virus particles could still creep in.

When a mask was placed on top of a cough, cotton and surgical masks prevented more than 50 percent of transmission of the virus.

“There was a synergistic effect when both the virus recipient and the virus distributor wore masks,” the researchers wrote in a study published on Wednesday.

There has been a growing consensus among health experts that the coronavirus can spread through the air. The U.S. Centers for Disease Control and Prevention revised its guidance this month to say the pathogen can remain in the air for hours.

A separate team of Japanese researchers used supercomputer simulations to show that moisture can have a significant effect on the dispersion of virus particles into the air.