A new study in the journal Proceedings of the National Academy of Sciences argues that of all the different tools we have to decrease the spread of the coronavirus, wearing a face mask might be the most important.

Researchers analyzed the different mitigation measures put in place in the three major centers of the COVID-19 outbreak — Wuhan, China, Italy, and New York City. They found that the number of cases started to drop the most when masks were made mandatory.

Their data also showed that airborne transmission of the virus through respiratory aerosols represents the dominant route for spread of COVID-19. Along with the data on mitigation strategies, they concluded that face masks are likely the major determinant of how the infection spreads or slows.

There are experts who disagree that masks make that much of a difference. Dr. Amesh Adalja, of the Infectious Disease Society of America, told ABC News he has yet to see much direct evidence to support making masks mandatory, especially when those coverings are homemade. He points to New Zealand as a place where the infection was controlled without widespread use of masks.

The debate over whether masks should be mandatory in public places will likely rage for months. But if you have to go somewhere where you can’t maintain your physical distance from other people, wearing a mask can decrease your risk of catching and spreading the coronavirus at least a little bit.