to fog up. if you are a young kid, you are wearing a mask and glasses and the classes start to fog up, you are going to be paying more attention to your fog to glasses the teacher. >> that's right. that is just one of a number of potential harms. it does inhibit breathing, so if we are doing this to children, we want to be sure that we are getting a real benefit. the available literature says we are not. it can be that glasses fogging up and creating difficulty learning. it can be difficulty breathing for some children. it causes some children to breathe through their mouth all the time, and on a sustained basis, that's not healthy either. beyond the physiological, you have mental health. the ability to transmit and receive communication on fear, sadness, happiness. all the things we communicate