ELI5 what is the science behind ‘masks help stop you spreading germs , but don’t stop you catching them’

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Let’s imagine that you are not wearing pants, you are drunk, and you just randomly piss. You might randomly piss on someone else. And no one else is wearing pants either so when they piss, they piss on you. Now imagine that you put on pants. And now when you piss the piss is mostly stopped by your pants and very little of it will get on anyone else. Other people would have to touch your pants to get your piss on them. But other people can still piss on your pants if they are not wearing pants. You still get their piss on your pants and it will soak through and your legs get wet from piss. Now imagine that everyone is wearing pants. Everyone pisses on their own pants and no one gets pissed on.


The best analogy I found was imagine you have a penis and you’re pissing yourself. If you don’t have pants on. Other people near you will get wet regardless of whether they have pants on of not If you do have pants on only you will get wet Germs/cold viruses usually spread through tiny water particles that humans breathe out all the time and a decent mask stops them


The flat masks that the majority of people wear are designed to simply stop us from projecting all of our germs on everyone else. Instead of blowing out a large plume of respiratory particles we just have small cloud around our faces. Air is still able to flow around our masks and thus we can still breathe in what is in the air around us. A respirator or n-95 type dust mask needs to be fitted, and when worn correctly will filter particles from the air. This will effectively reduce infection rates.


Partly the saying is overselling a bit, masks do help both ways, they’re just more effective at stopping spreading than they are at stopping catching. It’s because when you cough/sneeze/breath it’s not just gases that leave your mouth, there’s lots of small water droplets as well. The water droplets either fall straight to the floor because they’re too heavy or they float around and might slowly evaporate away leaving just the virus and whatever else behind. Masks are very good at stopping droplets which have recently been released but they’re less effective the smaller they get, the droplets are biggest when they’re first sneezed/coughed so that’s when a mask has the best effect. Also not all masks are equal, if you get yourself a good enough mask then it will basically be just as good either way.


Not all masks are the same. The n95, respirators, and similar high-quality masks are all capable of helping prevent germs from being inhaled or exhaled, whereas the basic cloth masks pretty much only stop the exhalation, because they aren’t as closely fitted to the face. So you don’t blast a huge cloud of particles with breathing or coughs, but you can still inhale anything that is airborne with the cloth masks. N95s and respirators have to be fitted to your face, and seal more closely than the cloth.