Is it true that masks only work to prevent germs/diseases from exiting one’s mouth/nose and not from entering one’s mouth/nose? If so, why?
In: Other
There are very many different types of masks and any of them can be fitted wrong or used wrong. So this does not apply to all masks. Most masks that is used by the general public to prevent the spread of disease is not effective filters against airborne pathogens. When the wearer breathe inn or out most of the air will pass unfiltered around the mask or between the fibers of the mask. But coronavirus is not an airborne pathogen, however it spreads through dropplets. These dropplets can be small enough to float in the air but still behaves very differently from airborne viruses. And while a mask may allow air to flow unfiltered through it most masks trap and collect a lot of dropplets and moisture. But this is mostly the air you breathe out. If there is viruses in small dropplets floating in the air from others it can easily find its way under the mask and infect you either way.
Masks reduce the outflow and inflow of airborne pathogens. They are, however, more effective at reducing outflow (at least your normal masks, not the special completely sealing masks).
The reason for this is simple. The mask does not fully seal on your face, there are little regions on its edges that still allow for some air to enter around and not through the mask. When you inhale, the air rushes into your lungs and takes the path of least resistance (or flows preferentially via it, but passes through many paths), and that path would be the small openings around the mask. That means if there are airborne pathogens all around you then chances are some will go with the air not going through the actual mask (hence not filtered).
However, when you carry the pathogen, then your breath contains it, and the exhalation via the mask, whether the air passes through or around the mask, ends up flowing sideways from your face, and whatever flows through the mask is filtered. This means the radius around you where the pathogen is spread is smaller, so it reduces the risk of infecting others.
Keep in mind its more complex than that, because some pathogens may spread only via coughing, when large aerosols are sprayed out and those easily adhere to surfaces (so a mask would make them adhere to your face and the inside of the mask), it’s not like single viral particles go flying around in the air on their own (thought that happens, depending on the pathogen and its load in your body). There is also the concept of humidity to consider. Your exhaled breath has a lot of humidity in it, so the inside of the mask would be wet, and you can also consider that for the filteration process in addition to the layer number, layer thickness, filteration hole radius in the mask and so on.
Edit: English
Depends on the masks. N95 masks can filter incoming air, but due to that filtering the airflow is slower and it’s harder to breathe regularly. However the masks that most people use during the current pandemic like surgical masks are not very filtering because the don’t form a perfect seal on the face.
Now wearing a mask prevents germ from getting out because of simple physics, when water droplets are propelled from your mouth they have energy pointing them in one direction, the mask makes a barrier that redirects the air. Water being heavier than air is harder to make change direction meaning it bumps into the mask and is caught along with the virus inside, while air molecules flow around and are expelled out the side of the mask. However it’s not perfect and smaller and lighter droplets can escape, but the mask has redirected the air and gotten rid of a lot of the energy that would carry it a distance. Thus reducing the transmission range significantly.
Now those gaps in the mask means that breathing in the air will want to take the path of least resistance and not flow through the cloth, thus flowing around the mask and taking any airborne particles with it and straight into your mouth and nose.
The mask prevents a lot of your own saliva from spreading into the air around you when you sneeze or cough, which has the bacteria in it. Note that it’s not completely stopping it because the air is moving over, under and sideways anyway so don’t go out if you’re sick, but it helps. Because you mainly breath the air coming from over the mask, it doesn’t stop other people’s germs from coming in. The mask also most likely doesn’t have any sort of filter to clean the air coming in through it, so the bacteria remains in the air you breathe.
I presume you’re talking about covid19.
Nothing in biology/medicine is only. In this case, the virus primarily spreads by respiratory droplets, little drops of virus-containing water that are expelled primarily when you cough and sneeze. The mask works as a barrier against these droplets. It works really well to prevent exit from your nose/mouth cause it’s right there to block it, but of course some can get through. The same goes for entry. It does something.
I haven’t seen numbers, but masks are far more effective for preventing exit than preventing entry, but that doesn’t mean they’re useless for preventing entry.
No, it is not. Masks are not directional. However! They seem to be *more effective* when they are stopping the wearer from spreading germs. The reason being; people in general can’t get Ill if the germs aren’t out there in the first place.
Masks can’t get all the germs, in either direction. But they severely limit the number of germs getting past. If you’re stopping them at the source (the cough) very few spread away from there and are much more easily “diluted”.
But if you happen to walk into a cloud of germs and breath in… you’re already in a cloud of germs. Most wont get through; but some will. And, that’s where you’re breathing. By definition.
the masks aren’t very effective at filtering, they simply limit how far your droplets fly, from several meters down to a foot or so. The mask doesn’t cover your eyes or other sensitive tissues that could get infected
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