Surgical masks may not actually protect you from the flu, but they can stop you from infecting other people if you do actually have the flu. One study published in the American Journal of Infection Control used samples of a harmless virus to test how effective the surgical mask is at protection from airborne pathogens. The study found that 20-85% of the stimulated virus actually penetrated the surgical mask in comparison to only 5% of another type of mask, a respirator. In another study, from the journal of PLOS Pathogens, investigators collected samples of exhaled particles from about 40 flu patients with and without the surgical mask. The results showed that a wearing a surgical mask significantly reduced the amount of aerosolized virus into the air. This proves that the main function of a surgical mask is not to protect the individual wearing it from catching any viruses, but to protect everyone else from inhaling the virus exhaled from the individual wearing the surgical mask.