A recent study has suggested that 23 per cent of people think that cabin air has made them ill.
John Quail, from personal injury firm claims.co.uk that commissioned the poll of 2000 adults, said that, along with high-profile cases of cabin crew claiming they are affected by aerotoxicity syndrome, it may soon be revealed that significant numbers of the general public may have been affected too, "especially business people and other regular fliers."
But how dangerous is cabin air really?
There's nothing more discomforting than sitting alongside a sneezing, wheezing traveller in cramped quarters for hours on end - particularly if, like I, you grew up in a germaphobic household. Recent studies might have you believe that these fears are well founded.
The findings of Auburn University in Alabama, which were presented at last year's annual conference of the American Society for Microbiology, revealed that disease-causing bacteria can survive for up to a week inside plane cabins, on surfaces such as seat pockets, tray tables, window shades and armrests. Staphylococcus aureus (MRSA), a bacteria that could cause infections, skin disease, pneumonia and sepsis, lived the longest (168 hours); Escherichia coli (E. coli), which can cause urinary tract infection, respiratory illness and diarrhoea, was found to survive for 96 hours.
The web is awash with equally worrying studies, which would suggest that every square inch of a plane is a potential habitat for germs.
CNN, back in 2010, highlighted six key "germ zones", perhaps the most surprising of which was the on-board water. It cites a 2004 study that saw water samples taken on board 327 different domestic and international aircraft. Some were found to have contained E. coli. Coffee and tea are brewed using this water, it said, but don't typically reach hot enough temperatures to kill E. coli.
More worrying still, it claimed that when bottled water runs out, some crew members have been known to fill passengers' glasses from the tank. Some planes were also said to sometimes refill their water tanks at foreign airports, where the water quality may not be so reliable.
Lavatories, it will come as no surprise, were also highlighted as areas of concern (or "smorgasbords of threat", to be precise). The US Centre for Disease Control (CDC) named the lavatory as one of the crucial "hot zones" for spreading diseases during the outbreak of the H1N1 and severe acute respiratory syndrome (SARS) viruses. The "thunderous volcanic" flushing action of the toilet exacerbates the health risk by launching germs from the toilet in all directions.
A report by The Wall Street Journal, back in 2007, claimed that airlines washed their blankets only every five to 30 days.
And in 2000, a US investigation of New York firm Royal Airline Laundry, which provides linen to several airlines, detected pseudomonas paucimobilis, a bacteria causing infections such as meningitis and urinary tract infection, on blankets, and traces of Aspergillus niger, a common contaminant found in food, on pillows.
Airlines, of course, tout their cleanliness. British Airways says it has "extremely high standards" with its planes being "thoroughly cleaned after each and every flight, including the seats, tray tables and aircraft toilets".
But it's a disquieting rap sheet.
So should we don gloves before reaching for that in-flight magazine? Or hold our breath during each trip to the loo?
Dr Richard Dawood, a travel health expert, suggested that you're just as likely to come into contact with germs on the way to the airport, and identifies dirty hands as the biggest trouble-maker.
"For most people, a journey affords a host of other opportunities to acquire infection: in the taxi to the airport, on buses and trains, in crowded departure lounges, and plenty of close contact with people at your destination," he advised a reader who developed an illness after a long-haul flight. "Those in-flight snacks should be avoided until you have had a chance to wash your hands."
While contact with germs on surfaces can be reduced or avoided, the fear of contracting airborne diseases might not be so easily dispelled.
Dr Dawood said the "virtually moisture-free" conditions inside a plane cabin increase your vulnerability to airborne infection. You're more susceptible to colds and respiratory infection, and viruses which are known to thrive in conditions of low-humidity.
"Coughing passengers can spread infection to those immediately around them, and in a small number of cases of more severe illnesses - such as TB [tuberculosis] - are known to have spread in this way," said Dr Dawood.
Aircraft manufacturers claim there's no difference between conditions found on a plane and those found on, say, a bus.
"The overall risk of catching a virus or any other germ from an ill person on board an aeroplane would be similar to the risk of contracting a disease on a bus, a subway, or train for a similar time of exposure," said Matt Knowles, a spokesperson for Boeing.
"High efficiency particulate air (HEPA) filters are used to remove particulate matter from the recirculated air including bacteria and viruses. The HEPA filters are used to filter about 50 per cent of the air in the cabin and this reduces the concentration of germs by about 50 per cent."
The total volume of air on a plane is said to be refreshed every two to three minutes, which - according to the Civil Aviation Authority - is more frequent than in most air-conditioned buildings, where the air is changed every five to ten minutes.
Perhaps the biggest health risk on a plane is when a flight is delayed and ventilation systems are turned off.
"Some of the best-known instances have occurred on the ground - such as a large flu outbreak following a prolonged delay on the ground - with ventilation systems switched off," says Dr Dawood.
A study was done in 1979 where an aircraft with 54 passengers on board was delayed on the ground for three hours, with the engine and ventilation system turned off. Within 72 hours, 72 per cent of those passengers showed cold and flu symptoms including a cough, fever, sore throat and headache.
There is another issue with cabin air. Cabin air pressure is maintained by using warm compressed air taken from the jet engines. This "bleed air" system is prone to contamination by oils that lubricate the engine, resulting in fumes entering the cabin space. Studies have suggested that toxic mixtures such as tricresyl phosphate (TCP) enter the cabin and may cause a range of neurological problems when consumed in large amounts.
For several years, concerns were raised over the possible health threats posed by the fumes. According to a report by the Aerospace Medical Association, published last April: "The UK CAA Medical Department in 2013 were aware of 28 individual cases who have reported symptoms which they attributed to exposure to fumes. Of these 14 have returned to flying or were never assessed as unfit. The remaining 14 remain unfit, although a number would have passed normal retirement age. No new cases have been documented since June 2012 and the CAA is not aware of any other on-going cases."
A report by The Committee on Toxicity (COT) in 2007 estimated that "fume events" were recorded on 0.05 per cent of flights overall and 0.018 per cent of passenger and cargo flights by UK carriers. Since that report, the UK Department of Transport commissioned a study of 100 flights in five different aircraft types, including Boeing 757, Airbus 319, 320 and 321 as well as the BAe146.
The study, done between 2008 and 2010, analysed air samples taken at various points within the aircraft and during all stages of the flight including the climb, cruise and descent periods. The results of that research showed normal levels of pollutants that didn't exceed any existing health and safety standards and guidelines.
Boeing is adamant that "cabin air is safe to breathe" and that "cabin air quality research has consistently shown that cabin air meets health and safety standards and that contaminant levels are generally low".
But this June, a group of former and serving cabin crew announced it is planning legal action against a number of British airlines, alleging staff were poisoned by contaminated cabin air.
They are being represented by Unite, the trade union, which set up a helpline for its cabin crew to report any incidents of aerotoxic syndrome. 17 staff were initially looking to bring civil claims, but according to Unite, which represents 20,000 flight crew, this number is expected to grow.
It comes after a coroner investigating the death of British Airways pilot Richard Westgate ruled in February that fumes circulating in planes posed "consequential damage" to the health of frequent fliers and crew.
Staying healthy in the sky
Dr Dawood offers the following tips:
Travel with alcohol hand gel, or antibacterial hand wipes, and use them before eating or handling food, and after going to the toilet (in addition to washing your hands).
Use a nasal saline spray, or a product such as Vicks First Defence, to keep the nasal passages moist during a long flight, reducing the risk of airborne disease transmission.
Consider the source of any food or water you are offered on board very carefully. On flights originating from places with poor hygiene, stick to bottled water and don't eat food unless you are convinced of its safety.
Stay hydrated. Immobility in a cramped seated position causes fluid shifts within the body, moving fluid out of circulation and into the tissues (evident for example as ankle swelling during lengthy flights). Most people should be drinking the equivalent of a litre of water during a six to eight hour flight in order to remain well hydrated, but most people drink much less during a flight than they would on the ground. Consequences include headache, fatigue, constipation, and in women, an increased risk of cystitis.
The Telegraph, London