Could air travel be making you sick?

Passenger plane above the clouds.

Nearly all of us suffer the effects of jet lag after a long-haul flight. It’s no surprise that travelling from one time zone to another in a cramped and dehydrating environment makes us feel under par for a few days afterwards.

But what if you are one of the many who have continued to feel unwell for weeks – or even months – after travelling by plane?

You may have wondered how it is that the very temporary discomforts of flying can possibly affect you for so long.

But once you learn that the air you breathe while on board is pumped in via the aircraft engines – yes engines – and can contain some of the most hazardous chemicals known to man, it’s no longer such a mystery. The collection of symptoms that can develop after breathing this air even has a name: Aerotoxic Syndrome. The symptoms range from short-term to long-term and from mild to serious, yet most who are affected have never heard of this condition and have no idea what is causing their ill health.

But if this is a little-known-about problem, that’s not because it’s an insignificant one, say those who’ve experienced it first hand. It’s because it is, in the words of one former airline pilot, “the aviation industry’s best-kept secret. They are literally playing Russian roulette with passengers’ health.” Let’s call this former pilot Captain X. He can’t be identified as he is in the process of suing his airline for the damage to his health suffered as a result of breathing contaminated air.

“Pilots, cabin crew and indeed all passengers are at risk of poisoning every time they fly,” says Dr Sarah Myhill, medical advisor to the Aerotoxic Association, an organization set up in 2007 to raise awareness of these issues and to campaign for airlines to adopt measures to protect passengers and aircrews. “Anybody who flies on a plane is at risk of Aerotoxic Syndrome.”

If you are reading about these potential risks for the first time, you will want to believe they don’t apply to the planes you have flown (or will fly) on. Unfortunately, the disturbing facts you are about to read apply to all airliners in service today, in all countries of the world. That’s the bad news. The good news is that, armed with the essential information that follows, you can make informed decisions.

Aviation’s inconvenient truth

At the altitudes at which airliners fly, the outside air pressure is very low so the cabin has to be kept supplied with a source of pressurized air to provide sufficient oxygen for those on board to breathe. Back in the 1950s, the first generation of airliners had compressors which took this air in directly from the outside. But aircraft engines have a plentiful supply of compressed air, so engineers soon realized that it would be cheaper to get the air from there. The new system (known as the “bleed air system”) became the industry standard during the 1960s and – somewhat incredibly – remains so to this day.

The air comes, specifically, from the compressor section of the engine. This section contains a row of fans, each of which runs on a sealed bearing which must be lubricated by engine oil. These seals – known as “wet seals” – are designed to leak tiny amounts of oil. The problem is that as the very high-temperature air speeds through this narrow section, the leaked oil vaporizes into it. The air is then cooled and pumped through to the cabin for passengers and crew to breathe. Hydraulic fluid can also get into the cabin air supply in a similar way.

Although inhaling air contaminated with these substances is clearly not an ideal scenario, it may not sound like such a big deal to you. After all, we live on a polluted planet and we all know that no matter how health-conscious we are, we can’t avoid exposure to toxic chemicals.

But most of us are unlikely ever to be in a situation where we’re inhaling chemicals as dangerous as those that are in jet engine oil – a complex synthetic oil designed to withstand the extreme environment of an aircraft engine. It contains (among other things) up to 5% organophosphates, added for their anti-wear properties. Specifically, it contains the group of chemicals which make up tricresyl phosphate.

Organophosphates are potent neurotoxins. They were developed during the early part of the twentieth century, and they were developed specifically to do damage to nervous systems. They’re used in insecticides and in chemical weapons (such as the nerve gas sarin, used in the May 1995 Tokyo underground attack). They are behind the link between “sheep dip” and neurological problems in farmers, and they are also implicated in Gulf War Syndrome. In short, organophosphates are known to be extremely damaging to health.

As mentioned above, tricresyl phosphate isn’t a single chemical; it is a group of them, and it is just one of many manmade chemical ingredients known to be in jet engine oil and hydraulic fluids. You don’t have to be a scientist to know that a cocktail of chemicals reacting together has the potential to be many times more dangerous than a single chemical.

But the chemical contamination does not end with jet oil and hydraulic fluid. Because engine parts wear over time, the cabin air supply can also contain vaporized heavy metals. For example, the fan blades located in the part of the engine the bleed air is taken from contain nickel, and nickel has been found at dangerously high levels in medical tests on cabin crew. Nickel is a known carcinogen.

Remarkably, there are no air filters between the engines and the cabin so those on board inhale whatever contaminants make their way from the engines into the air supply. No studies have ever been done to ascertain the health effects of inhaling these chemicals in an enclosed space – even though many of them are considered so dangerous that it is generally accepted there is no safe level of exposure.

Despite all of this, governments, airlines and airline regulators will tell you the air you breathe on board an aeroplane is safe. They will generally not dispute that jet oil fumes can get into the cabin air supply; they will only dispute that there is any evidence this can cause long-term health problems. For example, the UK Civil Aviation Authority says, “We reject claims that we are putting the travelling public at risk. Safety is and always will be our first priority.”

But ask any of the airline pilots – some of them barely into their 40s – who started their careers in perfect health and are now no longer well enough to fly and you will hear a rather different view.

John Hoyte is the former pilot who set up the Aerotoxic Association after his flying career ended in 2006 due to the effects of organophosphate poisoning. “If you breathe jet oil fumes in a confined space, guess what – it might harm your health,” he says. “Jet engine oil does what it says on the tin. It is 3%-5% organophosphates. Those who say that’s too low to have any effect – how do they know that? The effects have never been scientifically tested.”

Tristan Loraine is another pilot forced to leave the profession due to the health effects of organophosphates, and producer of the documentary Welcome Aboard Toxic Airlines. “There is little scientific dispute – except by airlines and the government – that vaporized oil can be harmful since it contains carcinogenic and neurotoxic organophosphates, the same lethal cocktail that is reported to be behind Gulf War syndrome,” he says.

Captain X, meanwhile, has this to say: “The bleed air system of pressurizing airliners is fundamentally flawed on health grounds. Every plane ticket should have a government health warning stamped on it.”

Campaign group Toxic Free Airlines is conducting an ongoing aircrew health survey. At the time of going to press, 910 airline employees from around the world (889 cabin crew and 21 pilots) have responded. 1 in 23 had been diagnosed with cancer – almost 10 times the average for the 35-50 age group into which most participants fell. 1 in 20 had been diagnosed with chronic fatigue syndrome (the average for the UK is between 1 in 250 and 1 in 1,000 depending on who you listen to) and 1 in 7 had taken more than a month’s sick leave during the previous year.

Behind the survey is former air stewardess Dee Passon. She was diagnosed with breast cancer in 2005, at the age of 47. In addition to cancer, she suffered a cascade of mysterious symptoms of declining health – symptoms which are no longer mysterious, as medical tests have revealed high levels of fuel-related substances in her cells, and nickel adducted to her DNA. Diagnosis: severe nervous system damage consistent with chemical exposure.

But it’s not just pilots and cabin crew who are being affected by cabin air toxicity, though they are certainly the group with the greatest risk due to their much higher exposure. Passengers are also being affected, and not just frequent flyers.

“In my small practice it is astonishing how many people say their chronic fatigue syndrome dated from a trip abroad,” says Dr Myhill. “The general assumption is that they picked up a bug whilst being in a foreign country, or a virus as a result of sitting in close proximity to other passengers, but the real truth is that they have been poisoned.”

She adds: “When I do fat biopsies on [affected] patients I find organophosphates in their fat and the level is measured in mg/kg – this is the same sort of level at which one would measure a drug if one were looking for therapeutic benefits. That is to say we are not talking about tiny doses. We are talking about therapeutic levels with the potential to cause great harm.”

Contaminated air events

So how likely is it that you have been exposed to potentially harmful chemicals during a previous flight, or that you will be exposed next time you fly? First of all, remember that the unfiltered bleed air system is currently used on all commercial airliners, on all airlines, and in all countries of the world, so there is no way of avoiding it if you fly.

In 2008, the investigative team at the BBC’s Panorama carried out covert testing during several routine flights and found organophosphates on board every time and everywhere they looked. “That doesn’t surprise me as I know how cabin air works,” says Captain X. “In my opinion, it’s likely that all passengers are being exposed on all flights.”

And this is the general consensus among the pilots who are campaigning for airlines to put safety measures in place to protect passengers: that it is not a question of whether there are organophosphates and other dangerous chemicals in the air on board; the only question is at what concentration, and this varies from airliner to airliner and from flight to flight.

The lowest exposure occurs when everything in this fundamentally flawed system is working as intended, so only trace amounts of jet engine oil make it into the cabin air supply. Some believe it’s possible that this might be all it takes to affect the genetically vulnerable, the health-impaired, the very young, the very old, and those with chemical sensitivities – if not after a single flight, then cumulatively. But the point is, no one really knows.

Then there are the “contaminated air events”. The engine parts concerned are subject to wear, and like any mechanical component, they may fail. Something as minor as a loose seal on a compressor fan bearing can cause much larger amounts of jet oil to leak into the cabin air.

How often do contaminated air events occur? That depends on who you ask. Official estimates range from 1 in every 2,000 flights (the UK government’s Committee On Toxicity, which looked into the problem of contaminated cabin air in 2007 ) to 1 in every 100 (the British Airline Pilots Association).

Don’t assume you would know about it if one occurred while you were on board. First of all, the airline is highly unlikely to tell you. Secondly, there won’t always be an odour, and if there is, it won’t necessarily be one that would alert you to the fact you were inhaling toxic chemicals. You’d be more likely to wonder about the personal hygiene of your fellow passengers, as the smell is described variously by pilots and cabin crew members familiar with it as “sweaty feet”, “old trainers”, “wet dog” and “vomit”. (Though some who’ve been exposed do use words like “burning”, “oily” and “chemical”).

Incidentally, not only are there no air filters between engine and cabin; there is also no detector to monitor the air quality and alert the crew when hazardous chemicals from the engines are starting to build up in the cabin. “The only ‘instrument’ on board to monitor air quality is the pilot’s nose but sense of smell is not something pilots are tested for at their regular medical assessments,” says Captain X. “Plus, some gases that can leak out, like carbon monoxide, are odourless.”

Industry insiders say that although pilots are often aware when a contaminated air event is taking place, it is rare that they will land early because of it, and the majority of events go unreported. “The pilot is under great pressure to get the passengers from A to B according to the flight plan so is unlikely to emergency-land the plane,” says Captain X. “The temptation is great to continue to destination.”

Although contaminated air events only occur on a minority of flights, that’s little consolation if you’re unlucky enough to be on one of those flights. In some cases the concentration of chemicals is high enough for there to be a visible mist in the air and/or for passengers who know nothing about Aerotoxic Syndrome or the bleed air system to be aware they are breathing contaminated air. These are the ones most likely to result in an emergency landing and an official report of the incident.

Then there are those flights where something goes seriously wrong but it’s not obvious at the time. For example, the February 2007 flight from London to Orlando during which at least 40 passengers dotted around the aircraft – many of them children – started exhibiting symptoms of illness. Three years later, some of them are still suffering from health issues dating from this flight and 20 of them are now in the process of suing the aircraft manufacturer. Had the return flight not been delayed, giving these passengers the opportunity to discover they weren’t the only ones who’d fallen ill and to compare notes on their symptoms, they may never have figured out what caused them.

“You don’t have to be too clever to realize that there are many other people out there who’ve been affected on flights like this one but don’t realize it,” says Hoyte. “Those people present themselves to their GPs [family physicians] saying they’re not feeling very well and don’t know why. This is responsible for an awful lot of ill health.”

What are the symptoms?

The above case is an extreme one but Dr Sarah Mackenzie Ross, a clinical neuropsychologist at University College London, estimates that Aerotoxic Syndrome could be affecting up to 200,000 passengers a year in the UK alone. “That’s a million in five years, and some of us think that’s a gross underestimate,” says Captain X.

“Affected by Aerotoxic Syndrome” can mean anything from a short-lived illness or depressive episode up to the long-term, debilitating chronic fatigue, cognitive impairment and neurological disorders experienced by the passengers on the aforementioned flight, and seen at such a high incidence in pilots and cabin crew.

Some of those affected say that the mental and emotional effects are the hardest to live with, and a few report that they have even felt suicidal. “Organophosphate poisoning rips you apart inside,” says Hoyte. “You feel like a different person and you don’t know why. Organophosphates affect your mood, your character and your personality – just speak to the farmers. This is not like a headache. It drills into you and affects your very being.”

The Aerotoxic Association points out on its website that the chemicals in aircraft air primarily affect the nervous system but that, “it’s not easy to predict how contaminated cabin air may affect you. People vary in how well they detoxify contaminants, so some can be affected after just one short flight’s worth of exposure to background levels of toxins, while others may be unaffected after years of such exposure.”

As Dr Myhill puts it: “The severity of the symptoms will depend not only on the dose of chemical that has been received, but also on the individual susceptibility of the traveller. We know from work done with the sheep dip flu and the Gulf War veterans that roughly a third of the population are poor detoxifiers of organophosphates. These people will be more severely afflicted.

“Obviously people with multiple chemical sensitivity will react much sooner than people who have not been sensitized to chemicals,” she says, adding that the short-term symptoms tend to be, “very similar to the mild acute poisoning that farmers suffer from with sheep dip, i.e. a flu-like illness with a bit of a headache, nausea, muscle aches, maybe irritation of the airways, difficulty thinking clearly, possibly low-grade fever and just generally feeling ill.”

Myhill says the short-term symptoms can also resemble the symptoms of alcohol intoxication: “Energy levels are markedly impaired, the brain does not work properly, one expects to see mood swings, irritability and psychiatric disorders.”

She says that while in most cases these symptoms will be short-lived, for a few susceptible individuals a long-term illness may be triggered, adding: “The difference between alcohol poisoning and poisoning by toxic chemicals is that when you stop drinking alcohol the problem goes away. The problem with toxic chemicals such as organophosphates is that they bio-accumulate in the body in fatty departments, particularly cell membranes.”

What’s the solution?

Governments have been aware of a possible problem with contaminated aircraft air for a very long time. The neurotoxic properties of organophosphates have never been in dispute – organophosphates were, after all, developed for that very purpose over 70 years ago – and the first well-documented case of cabin air toxicity occurred over 30 years ago.

But the problem has remained inadequately addressed, despite many government and industry statements recognising it. One of the earliest official investigations into the issue was the Australian Senate Inquiry of 2000, which acknowledged that crews and passengers exposed to aircraft air contamination were indeed becoming ill.

Ten years on, the agencies worldwide with the power to protect those who travel and work on airliners are still not doing so. They generally explain this inaction by pointing out that there is no proof of any link between contaminated cabin air and long-term health problems. “It’s no good governments arguing that the scientific case has not been conclusively proven,” says Loraine. “That’s ridiculous – the burden of proof is already such that they must act now.”

As more and more pilots, cabin crew and passengers connect the dots between their ill health and the chemicals that can make their way into the cabin air supply, the day is approaching when the industry will be forced to take action. But as that day does not seem to be imminent at this point, what can you do to protect yourself in the meantime?

The only way to eliminate the potential risks completely is to avoid flying completely. The effects of Aerotoxic Syndrome can be so debilitating that some sufferers find this a very easy choice to make.

If you are healthy, there is no need to swear off air travel altogether. But if contaminated air concerns you, the one thing you can do to minimize the risks on your next flight is to wear a protective mask. Organophosphate molecules are relatively large so they can be filtered out using a charcoal-based filter and the Aerotoxic Association sells such a mask. Cost: £5.

You could take this mask with you to put on if you notice any contamination of the air during your flight, or – if you wish to ensure maximum protection – you could wear it the whole the time you are on board. “Yes it would look very silly, and might even arouse suspicion from the cabin staff, but what’s the alternative?” says Captain X.

If you are wondering whether the drop-down oxygen masks offer passengers any protection in the event of a contaminated air incident, the answer is no. The oxygen masks are for use only in the event of a cabin depressurization – pilots are not allowed to drop them for any other reason – and in any case, they circulate cabin air so provide no defence against whatever is in that air.

As campaigners point out, it is the airlines who should be taking the responsibility for filtering the chemicals out of the air before it gets anywhere near passengers. And they argue that this is not only something airlines could easily do – but that they could recoup the cost of it with a price increase that would amount to just pence per ticket.

As well as installing air filters, there are two other simple and relatively cheap steps campaigners are pushing for: airlines could switch to oils which don’t contain organophosphates, such as the ones used on military jets, or they could install detectors to alert cabin crew when dangerous chemicals are building up in the air supply. “This is really obvious stuff,” comments Hoyte. “We push the solutions non stop: filter the bleed air, remove the organophosphates, and fit toxic fume detectors. As precautionary measures. Just in case.”

There is one piece of good news on the horizon. After more than 10 years in development, a new airliner will go into service later this year. Boeing’s Dreamliner 787 uses the much safer pressurization system which was abandoned decades ago – the air that supplies the cabin will come directly from outside rather than being fed through the engines first. It’s not in service yet and even when it is, it will be used on only a minority of flights unless and until the whole industry follows suit. Still, it is a definite step in the right direction.

At the time of going to press, nearly 900 Dreamliner 787s are on order from airlines worldwide – this is a record response to a new launch in the industry. “They’ll all say it’s for efficiency reasons but no one who knows about this problem believes that,” says Captain X. “They know the writing is on the wall. In the meantime, personally, I will not risk travel by airliner anymore.”

This article first appeared in Get Fresh! magazine.

For further information

The Aerotoxic Association

Toxic Free Airlines

Welcome Aboard Toxic Airlines (DVD)

Dr Sarah Myhill


  • You are really a great reporter. I remember this article from Get Fresh magazine … and I remember thinking it needs to be read by a much bigger audience. How long until a newspaper picks this up?

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  • I’ve read a lot on this topic but this is the best thing I’ve ever read. Agree with the commenter above that this deserves a much bigger audience.

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  • To learn the facts presented here, how people’s health has been and is being affected, and how this has been covered up instead of addressed … I am speechless.

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  • I flew jet blue from las vegas to jfk ny late friday march 29. The air smelled like burning metal and it was warm. I felt like vomiting for most of the flight and felt agitated. Usually I am able to sleep and the air feels cool. The passenger next to me complained that something smelled bad. I wondered if there was a sick plane syndrome, since I ‘ve known about sick buildings due to poor ventilation. I am shocked by how widespread this situation is! I plan to notify senator schumer and other elected officials.

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  • Very interesting. I have been traveling long haul every couple of months for the past year. I have been very ill after the most recent flights. I am more healthy now than I have been in a while but I am taken in for two to three weeks after these flights. Symptoms similar as described; flu symptoms, aching limbs headache nausea and dizziness, dry tickly cough, upset stomach, no appetite diarrhea.

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