This forum is about wrong numbers in science, politics and the media. It respects good science and good English.
O2 radicals exist transiently in all tissues for the purpose of respiration. Other free radicals are present in lysosomes, cellular organelles which exist in all cells but which in some immune cells (phagocytes) serve the purpose of destroying ingested bacteria. Here they are desirable, elsewhere they are undesirable and cause damage to your cells.
I personally do not believe (and I spent my PhD analysing the biological effects of several chemicals which are known free radical scavengers, how's that for point scoring?) that exposing yourself to reduced partial atmospheric O2 pressure for a few hours will have a meaningful effect on the ability of phagocytes to kill bacteria - particularly as free radicals are only one of several different approaches used by these cells. Occam's razor provides for a far more obvious source of "flyer's 'flu", namely the spending of up to several hours in confined quarters with up to 400 other people from hundreds of different places is bound to expose you to a large number of infectious bacteria, some of which you are unable to mount a primary immune response to before it causes disease.
But my beliefs and your beliefs, expressed as speculation on a web forum are of little merit in the world of empirical science. We need to do an experiment.
What I suggest, is that you endow me a chair at Manchester University as "Professor of Aviation Medicine", and I will give up my current day job to accept the position. In addition to the salary, I will need research funding for a three year research project consisting of a minimum of 12 return long-haul flights a year (about average for a professor these days anyway), business class of course, and %£60,000 a year for a postdoc, technician and PhD student plus lab space and consumables. I will have blood samples taken before and after each flight and analyse the free radical component of my phagocytes. I'm sure I can think of all sorts of other self-promoting experiments to do while flying around the world as well. What do you reckon?
I reckon I will start wearing masks on long haul flights OR just avoid them altogether.
According to some Australian researchers the oxygen levels are better on long-haul flights. They found 15% was a typical in-flight oxygen level, but on long-haul Boeing 747s, it was 17%.
Was that with or without large sections of the fuselage?
That piece is twaddle. They keep talking about higher when they obviously mean lower and v/v.
They say that cabin altitude pressure was higher on short flights. Well, that would mean more oxygen per breath, wouldn't it? - unless they meant that the cabin was pressurised to the pressure found in free air at a higher altitude. Either way, their writing skills need improvement.
Aircraft cabins are pressurised to the pressure found at about 8,000 feet (which saves carrying about a ton of air in a large airliner). However, since all gases are completely mixed in air at all levels (to a first approximation) the proportion of oxygen is still 21%. What matters for chemistry (and biochemistry), though, is the partial pressure, i.e. the pressure the gas would exert if it alone filled that volume. I think this is where our scientifically ignorant journalists are rather losing it.
Anyway, 8000 feet is only 50% higher than Denver, Colorado, USA and considerably lower than many locations in the Andes and Himalaya.
Know its been said before but… here goes. I have been a regular air traveller for the past 34 years , both long haul and short. I simply cannot remember there being all these problems for passengers prior to the smoking ban.
But what other confounding factors?
I used to fly quite a bit on business back in the 80s and early 90s. Usually in smoking areas back then.
Rarely was a plane full, especially in business class. So risks emanating from other passengers were fewer. The same could be said for airports.
Secondly some parts of the world, or travel relating to them whether directly (visiting) or indirectly (fellow travellers from those areas or planes that regularly visit those areas) are more risk likely than others. Expansion of air travel to and from such locations has most likely expanded over about the same period that smoking has been reducing and ultimately banned.
On balance I would guess that the likely cause would be reduced maintenance for reasons of cost reduction (or profit enhancement to put the other spin on it) and that such would have been the case in any event.
I rarely fly these days. It has become such a disappointing experience compared to earlier times.