Q. Am I right to worry about the quality of air on board planes? I always get off a long flight feeling fluey.
Malcolm Dugdale, London
Sunday Times Travel Doctor: Even though the air inside an aircraft is exchanged every two to three minutes, and modern airliners pass recirculated air through HEPA (high-efficiency particulate air) filters of the type used in hospital operating theatres, this counts for naught if the person sitting next to you has a cold or flu symptoms, and coughs or sneezes.
Assuming that your fellow passengers are healthy, the change in pressure on board an aircraft might contribute to your feeling unwell.
The cabin is pressurised to an altitude of about 7,500ft above sea level — lower than where altitude sickness would kick in, but high enough to accentuate your awareness of underlying ailments, the effects of alcohol and the onset of headaches.