Actually....the air is not "recycled", it's always fresh air from outside and heated to be comfortable. There are valves to keep the cabin presurized because a small amount of presurized air always leaks out in different places. So don't think it's contaminated air. It's from outside.

We don't stay healthy in fact a lot of us have tubes in ears or have had sinus surgery. The sick policy for us carriers is crazy for flight crew, and even though the air is not technically "recycled" it is not a safe working enviroment for flight crew pilots included. It is such a dry enviroment it kills your sinus cavity and your subjected to so many people in such a confined space we get sick often with everything you can think of. After awhile the immune system builds up a resistance but no matter how long you been doing it we still get sick more than average. We also cannot pop many OTC drugs while on duty like most people can at work to "get by" while working sick. We are forced to work sick pilots too, which that is a aafety issue for pilots def., yet commercial airlines could care less you would die if you knew how many pilots fly around with flu like symptoms for fear of job loss due to a ridiculous sick call policy. As of last week we are now protected under OSHA, about time, so hopefully some things will change. They should be disinfecting aircraft at the least daily and they are barely "cleaned" as it stands now. Also the block limit of daily duty days is inhumane. You would think after the studies came out two yrs ago saying driving with a common cold is like drunk driving in that it affecys reaction time that pilots would be considered unfit for duty but nope it will take a major disaster for airline management to realize their sick policy for flight crew is just plain dumb and a safety issue

Also a tip if you do fly again DO NOT drink coffee or hot tea i know for a fact that on some aircraft, not all but some, the pottable water is disguisting. In fact they found ecloi in the pottable water tank on a jet a few weeks back were i work. While i obviously cannot say were just be safe and realize no airline cleans those tanks the way they are supposed too. They drain is disguisting. I flew in a plane last week that had green stuff growing around the drain water that was served came from. I try not to serve it to people out of i feel bad doing so but i cannot voice that without getting fired so if asked i will make and serve coffee or tea but i NEVER offer those to people or even make coffee unless requested and most of the time if isnt alread made people will choose something else and i sigh relief yet possibly another G.I. bug dogged for some poor unsuspecting customer...

I flew cargo/passenger missions in the USAF in the 50's/60's. Our ground crews would run a very strong disinfectant mist through the vent system just prior to each flight. I have no idea what the stuff was, but it had a very pleasant smell. We seldom had any respiratory problems.