Most seasoned air travellers understand the risk of deep-vein thrombosis on long-haul flights and are familiar with the debate about recirculated cabin air (see page 32). But sitting inside our hermetically sealed aircraft, we assume the environment outside is something we don’t need to worry about. However, there is one thing that the aircraft fuselage is no barrier against, and that’s cosmic radiation. It is something that few travellers are aware of; in fact, in a survey on, 88 per cent of respondents said they had never heard of it. Periodically, headlines have drawn attention to possible links between cancer rates among air crew and exposure to radiation in-flight. Nowadays, though, many business travellers spend almost as much time as flight crew at altitude, so is there cause for concern?

Cosmic radiation is a form of ionising radiation (which also includes x-rays) and is part of the natural background radiation that surrounds us all. Unlike non-ionising radiation – which includes ultraviolet, infrared and radiowaves – ionising radiation can cause damage to cell DNA when it passes through the body. If this alters future copies of cells, it can eventually lead to cancerous growth.

It’s important to remember that the body is used to dealing with radiation, according to Michael Bagshaw, visiting professor of aviation medicine at King’s College London. “We’re exposed to radiation all the time – you’re getting it from your bones, from your teeth, from the rocks around you,” he says. “When the body is exposed to ionising radiation there is a possibility of damage to the cells. But the body is a wonderful bit of equipment and has great powers of repair. So exposing the body cells to radiation may well cause some damage but in nearly every case, that damage is self-repaired.”

The good news if you’re at ground level is that the earth’s atmosphere and magnetic field deflect most of this radiation, but at cruising altitude it is 50 to 100 times stronger.

While sudden high exposure to radiation has been linked with higher cancer rates, less is known about the long-term effects of low doses. Not surprisingly, most of the studies have been conducted on flight crews, since they are the most frequent flyers. Some studies have shown a higher rate of some cancers; for example, a study of 458 Icelandic pilots found they were 10 times more likely to develop skin cancer than the general population. Another study found a similar trend, but the results are complicated by the fact that pilots tend to be exposed to far more sunlight in the course of their working lives. Carolyn Evans, head of flight safety at the British Airline Pilots Association (BALPA), says: “All indications are that the only problem that occurs slightly more in flight crew than in the general population is malignant melanoma and we have always put this down to the availability of sunny beaches to flight crew.”

She adds: “We have concerns that cosmic radiation could cause cancer but we don’t have any proof that it has done so.”

Several studies of airline pilots have even found a lower mortality rate than the general population – which does make sense because pilots are deliberately selected for their health and fitness. One study of Air Canada pilots in service between 1950 and 1992 found an overall reduced rate for cancer – but it also found a significantly higher rate of one type of leukaemia and of prostate cancer. Confusingly, a later study involving British Airways pilots found no sign of increase in either of these diseases.

A study looking at 44,000 flight attendants from across Europe reported in 2003 that there was no increase in mortality that could be attributed to cosmic radiation. However, some studies have found significantly increased rates of breast cancer in female flight attendants. This too has been difficult to treat as a “smoking gun” because researchers have been unable to untangle the confounding factors, namely that flight attendants as a group tend to be smokers and have children later, both of which are risk factors for breast cancer. Bagshaw says: “There are so many confounding factors that it’s very difficult to put your hand on your heart and say it’s late childbirth, or it’s smoking, or diet or cosmic radiation – we just don’t know.”

Dr Mark Popplestone, head of passenger health services at British Airways, agrees: “There isn’t a great weight of evidence to support [a link with cancer] but you can’t categorically say there isn’t a risk. I welcome more, and better, studies about it so that we can put the issue to bed.”

In August, a study reported that commercial airline pilots were three times more likely to develop a common form of cataract than non-pilots; while there was no direct proof that this was due to cosmic radiation, the scientists concluded it “may be a causative factor”.

With the evidence full of uncertainties, it’s difficult to decide how much protection, if any, is needed for cabin crew and frequent flyers. The radiation exposure limit recommended by the International Commission on Radiological Protection (ICPR) is 1 milli-Sievert (1mSv; see above)per year for members of the public – over and above natural background radiation – and 20mSv for people who are exposed to radiation as part of their job. It may seem strange that there can be more than one safety limit for different individuals but the reason lies in the difficulty in defining “safe” amounts of radiation.

Bagshaw explains: “If someone is exposed to radiation as part of their occupation you’re saying, ‘OK, the body will still repair itself and there is no evidence of harm to health’, but because these people are working in this environment they know the risks and what’s involved, it’s therefore appropriate that they have a higher limit. You can’t work in a radiation environment and only get 1mSv.It’s just being pragmatic.”

To put these figures into context, the typical radiation level at altitude is 5 micro-Sieverts (equivalent to 0.005mSv) per hour for flights over polar latitudes – or, because the deflective abilities of the earth’s magnetic field are greater near the equator, around half that on equatorial flights. A flight between London and Japan for example, is around 60 micro-Sieverts (0.06mSv) in total, while a flight from London to Johannesburg is about 33 micro-Sieverts (0.033mSv). With these levels of exposure it is estimated that long-haul crew have an annual mean exposure of 4-5mSv and short-haul crew 1-2mSv.

It’s worth bearing in mind that you don’t even need to leave the ground to get a higher than average dose of ionising radiation; there are many parts of the world, including in the UK, where background levels are naturally much higher. Dr Michael Clarke, spokesperson for the Centre for Radiation, Chemical and Environmental Hazards at the Health Protection Agency, says: “If you’re a frequent flyer there’s no doubt you get a higher dose but it’s only equivalent to living in one of the higher background level areas of the country. In Devon and Cornwall you can get 8mSv a year, and the citizens ofDevon and Cornwall are no more or less healthy than anyone else.”

In 1991, the ICPR recommended that all flight crew who are likely to cross the1mSv threshold should be classified as “occupationally exposed”. An EU directive went further in 2000, stating that airlines should monitor the individual exposure levels of their cabin crew and should ensure that all cabin crew are educated about the possible risks of exposure. Flight crew are also covered separately by the UK’s Air Navigation Order, which sets a limit of 6mSv – above which their work schedule must be adjusted to ensure lower exposure.

Since it only takes 200 hours of flying over the poles per year – or to put it another way, eight transatlantic return journeys – many frequent flyers also exceed 1mSv, so logically, shouldn’t they be receiving the same educational support?

This is not mentioned in the legislation. Bagshaw says: “it would be reasonable for business travellers to be considered to be occupationally exposed.” But he points out that if the occupational limit of 20mSv is applied to frequent flyers, they would still be well within the threshold.

Dr Robert Barish runs a New York-based consultancy that aims to educate both crew and frequent flyers about the health risks of cosmic radiation. He believes that while the risk may be small, it is still the right of people to know what that risk is and to judge it for themselves. Regulations in the US have been slow to catch up with Europe in this area. Barish says: “An advisory was published in 1994 recommending that the subject be taught to air crew but it never became a regulation – it simply languished.

“You can have cabin crew members on a BA flight from JFK to Heathrow and people who leave on an American Airlines flight from JFK to Heathrow: the BA people will have had their radiation assessed as part of the European regulations and will have been educated about it because it is required, and the American people won’t know a thing about it. It’s difficult to understand how that can be allowed to happen.”

The same principle applies to American business travellers – but their European counterparts are no better informed. Is it up to employers to keep their roving staff educated? With no firm link between cosmic radiation and cancer and no regulations to enforce it, it seems unlikely that radiation training would be high on any corporate agenda.

One company in Denmark has come up with a new system for monitoring cosmic radiation exposure of flight crew that can also be used by companies. Launched in May, Globalog aims to provide more exact, minute-by-minute measurements of cosmic radiation than are used by many airlines. Many carriers use a computer program called CARI-6, which was developed by the FAA and calculates the dose on each route based on information such as latitude, altitude, date and time of flight. The figures are then retrospectively adjusted using “heliocentric potential” data on the level of sun activity.

Globalog takes more precise account of fluctuations in solar activity, which can be dramatic during periods when solar flares are most common. Spokesman Peter Mondi believes its accuracy will help airlines use their staff more efficiently. Pregnant crew members, for example, are often grounded as soon as they announce their pregnancy, as the EU directive sets them a limit of 1mSv but adds exposure levels should be as low as “can reasonably be achieved”. Mondi says: “With our system you can get more out of your human resources because we tell the flight operations manager once the crew member has reached within 10-15 per cent of the 1mSv limit.”

Companies can also register their staff on the web-based service, which allows them to plug in their flight details and receive feedback on their exposure for every business trip. For around E20 per month per employee, a company can receive a record of the exposure level of its staff.

Peter Mondi points out this may be particularly useful for staff of small companies who fly on private business jets, which fly at higher altitude than commercial aircraft (around 43,000ft instead of 37,000ft), leading to slightly higher exposure. Concorde used to fly at similar altitudes, but the journey took around half the time which compensated for the increase.

Should companies with frequent travellers invest in such a service? Professor Bagshaw says: “If a company wishes to extend a duty of care to its employees and wishes to treat its employees as occupationally exposed it might wish to record their annual exposure, but I personally don’t think it’s necessary – I fly as a pilot and I don’t record my exposure.”

He adds: “My concern is it raises an anxiety perhaps that is not required.”

A joint research project between Virgin Atlantic, the CAA and University College London’s Mullard Space Laboratory, has produced a database full of radiation readings covering 1,000 flight legs all over the world. These have been compared with the results calculated by the airlines’ software to verify that airlines are not using wildly inaccurate data to monitor crew. And the results? According to Mullard scientist Dr Bob Bentley, they were “accurate except during periods of intense solar flare”. As flares occur with little warning and only last a matter of minutes or hours, they are difficult to record, and their effect on the radiation dose is still poorly understood. But Bentley says the results have shown that the software programs are accurate enough for most flyers: “For average activity it’s not far off – if you’re interested in whether you’re getting 3mSv per year or 6mSv per year, you would be getting that from this data.”

Bentley is part of the UK-based Cosmic Radiation Advisory Group, which draws up guidelines for airlines with advice for crew. But what about frequent flyers? He says: “This is something that has not been decided: if a company should have a duty of care to its employees whether or not it is an airline. Whether it will in the future is an open question; we think it’s only a matter of time before it will.”

Ultimately, Michael Bagshaw thinks cosmic radiation should be of little concern to frequent flyers: “The lifetime risk of developing a cancer for a British male is 23 per cent. If you are exposed to cosmic radiation of 6mSv per year for a flying career of, say, 25 years you increase your risk to 23.4 per cent. Compared with all the other risks in life, I think that is unimportant.”

What is cosmic radiation?

Cosmic radiation comes from two main sources: the first is high-energy radiation from outer space, called galactic cosmic radiation, which is believed to come from exploding stars. A smaller amount comes from the sun when a disturbance in the sun’s atmosphere — known as a solar flare — propels particles through the upper atmosphere.
The intensity of cosmic radiation depends on an aircraft’s altitude and latitude, and on the stage of the solar cycle. The sun’s magnetic field varies in strength over an approximate 11-year cycle, but the relationship between the sun’s activity and the amount of cosmic radiation is not what you might expect. When the sun reaches its peak of activity (the “solar maximum”) its magnetic field actually deflects particles away from the earth, reducing the amount of galactic cosmic radiation entering the atmosphere by about 20 per cent. Periodically solar flares also contribute to cosmic radiation levels, but they are unpredictable and their impact is poorly understood.

Measuring cosmic radiation

Cosmic radiation is measured in Sieverts (Sv), a unit used to describe the absorption of radiation by the human body. The levels of cosmic radiation are very low and are measured in milli-Sieverts(mSv; one-1000th of a Sievert) and micro-Sieverts (one-millionth of a Sievert).

Find out more

To download a copy of Cosmic radiation in commercial aviation by Michael Bagshaw, published by the International Academy of Aviation and Space Medicine, visit and click on publications/position papers. For more information on cosmic radiation, visit or the Health Protection Agency at

Virgin Atlantic does not publish advice on cosmic radiation on its website but a spokesperson told Business Traveller: “It is something we are committed to investigating and we are starting further trials next year.” (Bmi did not want to comment on its policy.)