The COVID-19 virus is somewhere around 0.1um or 0.1 micrometres in size. While the standard N95 (PM2.5) mask will stop something around 0.5um or 0.5 micrometres in size. So how small is all this anyway, well in comparison a single red blood cell is 7um in size (not a drop of blood, but a single cell of blood). So they are correct the mask will NOT stop the virus from penetrating the mask and passing right through it.
But what most people are failing to understand is that you have to come into contact with the virus first. The virus generally isn’t just free-floating in the air, lurking, waiting for someone or something to attach itself to. It isn’t a spider or a tick, it is generally already affixed itself to someone or something (now of course if someone coughs directly you on, you could be exposed, but then again they could likely get throat punched by you as a gut reaction – (sorry that is the Marine in me, peeking out). Now I know there is a ton of data that argues that the masks are ineffective (https://www.cidrap.umn.edu/
If you are a doctor or nurse and your patients are coughing or spreading other body fluids, then a mask isn’t very effective, but if you wear a face shield along with a mask, then the virus has to get across the void between you and the patient, then around the shield and then the mask and into your respiratory. This is called mitigating your risk and you do that by lessening your direct exposure to the virus.
This is why it is so important that you wash your grubby little paws with soap and water, you are mitigating your risk. You are more likely to touch something that the virus has attached itself to and then you touch your face and bring the virus that much closer to your respiratory system or mucus membranes.
Once it is near your respiratory system or mucus membranes (eyes, ears, inside your nose, inside your mouth, lips…)
See COVID-19 is a virus that mainly attacks the respiratory system of its victims. So that is why you want to wash your hands and why gloves are pretty much ineffective for the average citizen. What makes them even more ineffective is how the average citizen wears the gloves, but that is for another post.
So even though a mask will not stop the virus from penetrating the mask and entering the area the mast is covering, it is a layer of mitigation and for the average person is a smart level of protection. Now if you are in an area that is very prone to the virus and just about everything in that area is infected, then your mask isn’t going to afford you that much protection.
Now if you are just wearing a mask in your car and you have the windows up and you are alone, then wearing a mask isn’t going to help you much, and you look like you are in a panic, that is unless you live in an area like San Bernadino where you could end up in jail or a $1000 fine for not wearing your mask, even in your car.