Eliot C. Heher, MD Air travel is extremely safe, but as most of us who fly frequently know you can end up pretty uncomfortable on even a short flight.
Older aircraft tend to filter air and mix in part fresh air before recirculating it in the cabin.
Newer aircraft tend to use almost all recirculated air. Often when the plane is on the ground the recirculation, filtering and air conditioning systems aren't completely functional so the air may be of worse quality than when you're inflight. Airline cabin air is extremely low in humidity. Your eyes may become dry and uncomfortable as well. Airline cabin air is low in oxygen relative to fresh air on the ground.