What is Aerotoxic Syndrome?

Aerotoxic Syndrome is the name given to the illness caused by the long-term effects of breathing contaminated cabin air in an aircraft. The term was introduced on 20th October 1999 by Dr Harry Hoffman, Professor Chris Winder and Jean Christophe Balouet, Ph. D.

Why does the cabin air get contaminated?

In order to have a comfortable environment and sufficient air pressure in the cabin to breathe at the altitudes at which airliners typically fly, a supply of warm compressed air is required. This is supplied direct from the engines and is known as "bleed air". It is mixed inside the aircraft with recirculated cabin air at a ratio of about 50/50.  Although some of the air is recirculated, all of it originates in the engines. Bleed air comes from the compressor section of the engine which has many moving parts which have to be lubricated. There are various engine seals in place which are designed to keep the lubricating oil and air separate. Due to the design of these seals "wet seals", they cannot be 100% effective, and will let a certain amount of oil into the air. They are also subject to wear, and like any mechanical component, they may fail. If a large amount of oil mixes with the very hot compressed air, the result will be fumes or smoke entering the cabin. This is known as a “fume event”. There are no filters in the cabin air supply to stop this happening.

How often does a “fume event” occur?

A UK government website states that fume events occur on 1 flight in 2000, while another report (see para 69) says the figure is 1 in 100. However, on some aircraft types crews report that they experience fumes to some degree on every flight. The fact that there is still no fume detection equipment on aircraft, and that the definition of "fume event" is not always agreed upon makes it very difficult to give a true figure.

Can I tell if the cabin air is contaminated?

You may be able to see a bluish haze or smoke in the cabin, or be able to detect it by smell. Descriptions such as sweaty socks, wet dog, vomit, sweet oily smell have been used. Background levels of contamination may not be detectable.

Why are the fumes so toxic?

A complex synthetic oil designed to withstand the extreme environment of the engines is used. It contains many toxic ingredients, including Tricresyl phosphate which is added as an anti-wear agent. It is an organophosphate, and is known for its neurotoxic properties. Indeed, organophosphates are used in the manufacture of pesticides and nerve agents. Contaminants may become pyrolised (burned) in the hot bleed air and form new products, and the synergistic effects of all these chemicals on the body are not fully understood. In addition bleed air may contain particles of heavy metals from the engines, such as nickel, cadmium and beryllium.

What are the symptoms?

Symptoms may be acute, i.e. for a short time after a flight, or chronic, i.e. long-lasting. Any number of the following may be experienced:

• Fatigue – feeling exhausted, even after sleep
• Blurred or tunnel vision
• Shaking and tremors
• Loss of balance and vertigo
• Seizures
• Loss of consciousness
• Memory impairment
• Headache
• Tinnitus
• Light-headedness, dizziness
• Confusion / cognitive problems
• Feeling intoxicated
• Nausea
• Diarrhoea
• Vomiting
• Coughs
• Breathing difficulties (shortness of breath)
• Tightness in chest
• Respiratory failure requiring oxygen
• Increased heart rate and palpitations
• Irritation of eyes, nose and upper airways.

As the term “Aerotoxic Syndrome” has yet to be officially recognized, many medical practitioners are unaware of the condition, so may diagnose sufferers with illnesses such as psychological or psychosomatic disorders (i.e. they’ll tell you it’s all in your mind), Chronic Fatigue Syndrome (CFS), Multiple Chemical Sensitivity (MCS), “mysterious” viral infections, sleep disorders, depression, stress or anxiety. 

Although some of these disorders may be a symptom of Aerotoxic Syndrome, the diagnoses on their own may not be very helpful as the root cause of the problem needs to be addressed.

Is Aerotoxic Syndrome treatable?

For mild cases, the effects are usually reversible and will resolve themselves. But with more severe symptoms, neurological damage may have been caused, which may take longer to recover from, or permanent damage may have been caused. There is no magic cure, but we can suggest specialists who may be able to help, or strategies to aid recovery. The first step is to recognise the problem, and avoid or limit further exposure to toxins as far as possible.

Can anyone get affected?

Primarily the toxins affect the central nervous system. It’s not easy to predict how contaminated cabin air may affect you due to genetic variability of individuals. One person’s body may have less success than another’s at detoxifying contaminants and so be affected after just one flight of breathing background levels of toxins, while another may be unaffected after years of such exposure or after a serious fume event with visible smoke in the cabin.

Symptoms may be short-lived or remain long-term, but with repeated exposures they may become more severe and last longer. Therefore, over time acute symptoms may join together and become chronic. After one serious fume event, it is possible the person may show no symptoms initially, but then start to feel ill a few days after the flight. Anyone in the aircraft can be affected, whether they be pilots, cabin crew, passengers, first class, economy, royalty etc. etc.

Airlines provide no protection against fume events. The aircraft drop-down masks partially recirculate air, so would not be effective at removing contaminants. They are designed for use only during a loss of cabin pressure.

Are all aircraft prone to engine oil leaks?

All jet aircraft including turboprops are susceptible to fume events and therfore may cause health problems leading to Aerotoxic Syndrome. Some have a worse history of fume events and associated Aerotoxic Syndrome. Top of the offenders list are the BAe 146and Boeing 757. However, the new Boeing 787 Dreamliner is the first new aircraft in over 40 years to use non-bleed air technology and will provide a clean supply of cabin air.

How long has this problem been known about?

The first well-documented case was of a C-130 Hercules navigator becoming incapacitated after breathing contaminated cabin air in 1977. The neurotoxic properties of organophosphates have been known about since before the Second World War.

Is there a solution?

Boeing’s new 787 Dreamliner is the obvious answer as it eliminates the possibility of cabin air contamination by engine oil. Instead of bleed air, cabin air is supplied by electrically-driven compressors.

In today’s existing bleed air aircraft, the quality of cabin air could be improved, and the risk of contamination by engine oil reduced with these solutions, all of which could be easily and relatively cheaply implemented:

• Installation of bleed air filtration systems
• A less toxic oil formulation. The French company NYCO already has a suitable oil available with approved for use in most airliners.
• Contaminated air detectors in the bleed air supplies

Is the aviation industry addressing the issue?

Various governments and regulating authorities have commissioned research, but so far have not been able to conclusively prove a link between contaminated cabin air and chronic health problems, although numerous independent studies show clear evidence of this link. Corporate profit, conflicts of interests and ineffective control by government and regulating authorities means that the industry as a whole remains in denial of this problem.