The term "cosmic radiation" refers to any radiation that originates in outer space, that is, outside our solar system. It is composed of subatomic particles and "rays" of energy such as gamma rays and X-rays.
Some of this radiation reaches earth every day, however the earth's atmosphere absorbs much of it before it can reach the ground.
Another source of electromagnetic radiation is produced by bursts of energy from the sun. These radiation-producing events, known as "solar flares," occur from time to time rather than continuously.
The earth's atmosphere acts as a sort of radiation shield around our planet. At ground level, we benefit most from this shielding effect, but when we fly, we travel to altitudes where the atmosphere is thinner, leaving us more exposed to cosmic radiation.
The atmospheric layer is heaviest around the equatorial regions of the earth, and gets thinner the farther we travel away from the equator. The atmosphere is thinnest near the earth's north and south poles. As a result, the farther we travel to the north or south, away from the equator, the more exposed we are to cosmic radiation.
There are three main factors that can affect the amount of exposure to cosmic radiation:
Since solar flares also can emit significant amounts of harmful radiation, crews flying during periods of this kind of solar activity may be exposed to additional doses.
Anything that is situated between us and the radiation can serve as a shield that either absorbs or deflects some of the energy. As mentioned above, the atmosphere is such a shield; an aircraft also shields us when we are inside it. But we are never completely shielded from cosmic radiation.
Cosmic radiation is composed of rays and subatomic particles that can penetrate matter. When they do so, they can displace electrons from atoms or molecules that they pass close to or hit, a process called "ionization."
When any matter is "ionized" its basic composition is changed - we might even say it is damaged.
Both the International Commission on Radiological Protection (ICRP), and the US Federal Aviation Administration (FAA) officially consider aircrews to be occupationally exposed to ionizing radiation.
In other words, by the very nature of their work, aircrews are acknowledged to have a greater exposure to cosmic radiation than most of those who are in earthbound occupations.
Flying, especially at the higher altitudes common to long-haul flights, can expose crews (and passengers) to levels of cosmic radiation many times greater than they would receive on the ground. Those flying in higher latitudes, and especially so-called "polar routes," are exposed to still greater doses of cosmic radiation than those flying in the middle latitudes.
Passengers on a given flight are exposed to the same radiation dose as the crew on that flight. But since aircrews fly again and again and again, for years, crewmembers are occupationally exposed to a cumulative dose much greater than virtually any passenger, including "frequent fliers."
Pilots are exposed to greater doses than cabin crew, since the passenger cabin provides more shielding than the cockpit.
Many commercial carriers, and government agencies in a number of countries, have conducted research aimed at measuring the radiation doses that crews are actually subject to.
Crews participating in such studies wear personal radiation monitors -- small badges similar to those worn by X-ray technicians and others who work in occupations that expose them to radiation continuously. The material inside the badges absorbs radiation energy. That material then can be analyzed in a laboratory to determine the amount of radiation exposure for the period of time during which the badge was worn.
Ionizing radiation can damage the molecules that living cells are made of. At smaller doses, the damage usually does not lead to any sort of problem.
High doses of radiation can cause enough damage to cells to affect their biological function. Lengthy or frequent exposures to smaller doses can have a cumulative effect and can have negative consequences resembling those of single high doses. The damage can result in health problems.
It is known that prenatal exposure to high doses of radiation has the potential to harm an unborn child. The effects of ionization can change the cellular structures of a developing fetus and can produce genetic defects.
Crewmembers who become pregnant should immediately advise their employer, and request that appropriate adjustments be made to their flying schedules.
Note: Women Pilots and Flight Attendants who are pregnant, or who plan to become pregnant, are strongly urged to read this free report from the FAA's Civil Aeromedical Medical Institute:
There also is some evidence to suggest that the kind of radiation exposures experienced by aircrews can contribute to the kinds of cell damage that leads to cancer. However, most cancers can arise from multiple causes such as a person's genetic characteristics, diet, smoking history, exposure to carcinogenic chemicals or substances, and so on.
So far, it has been impossible to determine unequivocally that aircrew exposure to cosmic radiation directly causes cancer. At the same time, however, it is probably safe to say that crew radiation exposure may play some sort of contributory role.
If you fly for a living, you simply cannot avoid occupational exposure to cosmic radiation. However, you can monitor the dose that you receive. By doing so, you will at least know if the amounts of radiation you are being exposed to are approaching levels considered to be dangerous.
There are several ways to do this.
A number of carriers and government agencies now monitor aircrew radiation exposure by supplying crewmembers with personal monitors, to be worn on every flight. Periodically, the monitors are turned in for analysis, and replaced with new monitors.
If the carrier you work for does not currently provide such personal monitors to its crewmembers, you and your flying partners should consider asking for them.
If you belong to a union, urge your union representatives to bring up the issue of radiation monitoring to carriers, on behalf of the union membership.
Whether or not you are able to make use of personal radiation monitoring devices to measure your exposure to cosmic radiation, you still can get an estimate of the dose you receive on a given flight. The FAA Office of Aerospace Medicine provides a free Radiation Calculator program that you can use to calculate your in-flight radiation doses.
Here are some trustworthy on-line sources for more information about Aircrew Exposure to Cosmic Radiation.
What is Ionizing Radiation? - World Health Organization, 2012
Cosmic and Solar Radiation - AFA-CWA: Air Safety, Health & Security Dept., July, 2006
What Aircrews Should Know About Their Occupational Exposure to Ionizing Radiation - W. Friedberg & K. Copeland, Civil Aerospace Medical Institute, Federal Aviation Administration, USA, October 2003 [PDF format]
Protection of air crew from cosmic radiation: Guidance material - UK Department for Transport, May 2003 [PDF format]
Galactic Cosmic Radiation Exposure of Pregnant Aircrew Members II - J. Nicholas, K. Copeland, & K. O'Brien, Civil Aerospace Medical Institute, Federal Aviation Administration, USA, October 2000 [PDF format]
Air crew radiation exposure -- An overview - S. Bailey, Nuclear News, January 2000 [PDF format]
Radiation Exposure of Air Carrier Crewmembers II - W. Friedberg, E. Darden & K. O'Brien, Office of Aviation Medicine, Federal Aviation Administration, USA, January 1992 [PDF format]
CARI-6 Radiation Calculator for Aircrews - free software download from FAA [link goes to info page about the software]
Solar Radiation Alert Regions - FAA Office of Aerospace Medicine, Civil Aerospace Medicine, USA
Space Weather Advisories - Official Space Weather Advisory Bulletins issued by the NOAA Space Environment Center (SEC), Boulder, Colorado, USA [regularly updated]
In the interest of facilitating further research on the topic of Aircrew Exposure to Cosmic Radiation, we have compiled a list journal articles and other references related to the topic.
Some of the items listed were used as source material to prepare this page.