After tons of experience I figured out the cure to the common cold. It’s very simple actually. Open windows and let your house ventilate and you’ll start to get better in like an hour. Then, unless you have a very good reason to keep windows closed (ie: a bad fire outside or toxic air outside for some reason) always keep at least one window slightly open with no obstructions in the way of its ability to ventilate the entire house almost at all times (except for when no one is home, then it’s OK to close all your windows to lock them). Even if it’s cold, wear warm clothes if you have to or turn on the heater. and air filters aren’t good enough, you need constant gas exchange between the air in your house and the air outside your house. Try it, it really works. I suspect many many health problems and a lot of bad health in general is caused simply by poor ventilation.