The intolerance of some passengers with regard to inflight air conditioning is understandable. However, according to commercial jet manufacturers, that air is just as clean, if not cleaner than the air we breathe on the ground. Such air goes through high-efficiency air particle separation filters called HEPA (High Efficiency Particulate Air). The total air volume in the cabin is renewed every three minutes. In commercial jets, the cabin altitude is kept at 7874 feet when the aircraft is cruising at around 36000 feet. This mountain air is assimilated by almost all passengers, although it represents a 25% reduction in oxygen.

The main inconvenience of inflight air conditioning is its low humidity. Since its creation in the 1940s, lack of oxygen and low humidity challenge the best brains in aerospace engineering. For a simple reason: denser air would require an increase in the internal pressure inside the cabin, which would increase the weight of the fuselage. In relation to air humidity from the engine compressors, this is a matter of Physics. At subzero temperatures at 36000 feet, air humidity is very low. It would be possible to add some moisture to the air in the cabin, but this would result in an increase in corrosion due to condensation. Such event is more feared than an increase in weight. Low cabin humidity is partially caused by the vapor exhaled by the passengers.

New jets like the  Boeing 787 Dreamliner  and the Airbus A350XWB will offer an innovative new air conditioning/pressurizing system that will lower cabin altitude from 7874 feet to 5900 feet and the humidity level will oscillate between 20% and 25%. This is a huge improvement, thanks to new compound materials (resins reinforced with synthetic fibers, especially carbon-fiber), which replace aluminum in the fuselage. The discovery and improvement of these materials will be responsible for the first big leap in the quality of inflight air conditioning since its early beginnings, around 60 years ago.