Most people breathe through their mouth. Putting a face mask on your face that covers your nose and mouth concentrates your exhalant and guarantees more viruses than normal can enter or re-enter your lungs thereby increasing the possibility to be infected by and even smaller amount of viral material than would happen without the amount of the virus being concentrated. A mask helps infect people who would otherwise not be infected. A better solution is to simply cover your mouth when you cough or sneeze. The old fashioned way was to simply cough into your hand or your elbow. Then wipe your hand with a tissue or handkerchief.