"A 2008 systematic review, published in BMJ, found medical masks halted the spread of respiratory viruses from likely infected patients. In particular, studies on the 2003 outbreak of SARS — a cousin to the coronavirus that causes Covid-19 — found that masks alone were 68 percent effective at preventing the virus. By comparison, washing hands more than 10 times a day was 55 percent effective. A combination of measures — hand-washing, masks, gloves, and gowns — was 91 percent effective."

https://shouldiwearafacemask.com/