There is no question among scientists that wearing one mask is better than not having any mask at all at combating the coronavirus. But with a more contagious variant strain of the coronavirus spreading worldwide, there are questions being raised on whether a single cloth mask is enough to stop the spread of the virus.

Dr. Anthony Fauci said on Monday’s “Today” show on NBC that wearing two masks likely gives more protection than a single mask.

“So if you have a physical covering with one layer, you put another layer on, it just makes common sense that it likely would be more effective,” Fauci told Today. “That’s the reason why you see people either double masking or doing a version of an N95.”

The CDC’s guidance has long been that cloth masks should have at least two layers. The CDC has not recommended the public use N95 respirators as N95s should be reserved for health care workers.

Outside of the US, public health officials in some nations are telling the public to only use medical-grade masks. According to CNN, Germany and France both have started requiring the use of medical grade masks in public, and one region of Germany has gone as far as to require the use of N95 respirators.

The World Health Organization has recommended that masks have at least three layers, but has also recommended that surgical masks and N95 respirators be reserved for health care workers.

CDC data shows that a two-layer cloth masks blocks 50 to 70% of fine droplets and particles in addition to limiting the forward spread of those particles.