Radiation is a major environmental carcinogen. The most important distinction in terms of health is whether the radiation is ionizing or non-ionizing. Ionizing radiation has enough energy to remove electrons from atoms, which turns them into ions and creates free radicals. Cancer is the illness most commonly associated with ionizing radiation, because it damages the DNA in cells. Cells that are rapidly dividing, such as those in infants in growing children, are most sensitive to ionizing radiation. Pregnant women in particular should try to avoid ionizing radiation.

 Ionizing Radiation

 Everyone is exposed to some naturally-occurring ionizing radiation from cosmic rays and radioactive elements in the earth. There is also human-made ionizing radiation, from nuclear weapons and nuclear power plants, medical tests and treatments, and other sources such as food irradiation and some consumer products. The amount of cell damage is related to the dose of radiation, but even a tiny dose could cause changes that might develop into cancer years later. There is no level of ionizing radiation that is considered safe.

The following chart shows the annual U.S. estimated radiation dose per person for ionizing radiation.

Source Average annual effective dose in millirems (mrem)
Radon and other radioactive matter we eat, drink, or breathe 257
Radiation from soils, rocks, building materials  21
Cosmic/cosmogenic radiation  33
Human-made sources 311
Total  622

As you can see, we get about half of our annual exposure from human-made sources.

The types of cancers most directly linked to ionizing radiation are cancer of the thyroid and of the bone marrow, called leukemia. They may develop within a few years of exposure. Other types of cancer resulting from ionizing radiation take 10-15 years or longer to develop. Cancers commonly caused by ionizing radiation include breast cancer, lung cancer, skin cancer, multiple myeloma, and stomach cancer. We can expect to see these cancers turn up in a few years in survivors of the 2011 Fukushima Daiishi nuclear disaster, and maybe farther afield as well.  Of course, if a particular part of the body was exposed to radiation, that is the region where cancer would be most likely to develop. Since the breasts and the lungs are located near each other, this is thought to be the reason that people who receive radiation for breast cancer are more likely to develop lung cancer later. Children are at higher risk than adults.

Since cancer comes from multiple causes, each person’s chance of developing cancer depends not only on the type and dose of radiation, but also on the person’s exposure to other carcinogens, the health of the person’s immune system, and genetics. We can’t tell the difference between cancer caused by radiation and cancer caused by other carcinogens.

Natural background radiation

The most common type of ionizing radiation is called natural background radiation, and it comes from cosmic rays and from radioactive elements in the soil. Cosmic rays are radioactive particles that hit the earth from outer space. Because the earth’s atmosphere blocks some cosmic rays, exposure is greater at higher altitudes. This means that people who live in the mountains are exposed to slightly more cosmic rays than people who live at sea level. People are also exposed to higher levels of cosmic rays during airplane flights. Airline pilots and flight attendants, who spend many hours at high elevations, are exposed to more of these rays. They likely have a higher risk of cancer, but the research on this is not clear.

People are also exposed to small amounts of radiation from radioactive elements that occur naturally in rocks and soil. Some may end up in building materials used in houses and other structures. Small amounts of radiation may be found in drinking water and in some plant-based foods as a result of being in contact with the soil. Tobacco products contain low levels of radiation, which may come from the soil it’s grown in and/or the fertilizer used to help it grow. We also come in contact with ionizing radiation as a result of the mining and burning of fossil fuels (coal, oil, and gas), the mining and smelting of some metals, and production of minerals such as the potassium or phosphorus used to make fertilizer.

The largest source of natural background radiation for most people is radon. This is an odorless, colorless gas that is formed from the breakdown of radioactive elements in the ground, such as uranium and thorium, which can be found at different levels in soil and rock throughout the world. Radon gas in the soil and rock can move into the air and into ground water and surface water. Some radon can be found in building materials, such as granite kitchen countertops. Radon gas will dissipate outdoors, so most human exposure to radon occurs indoors, where it can build up. The levels of radon in homes and other buildings depend on the characteristics of the rocks and soil in the area.

As a result, radon levels vary greatly in different parts of the United States, even within neighborhoods. Elevated radon levels have been found in every state.

People who work underground, such as some types of miners, are among the most likely to be exposed to high levels of radon. High death rates from lung problems among miners in some parts of the world were first noted hundreds of years ago, long before people knew what radon was. Studies of radon-exposed miners during the 1950s and 1960s confirmed the link between radon exposure and lung cancer. Higher levels of radon exposure are also more likely for people who work in uranium processing factories or who come in contact with phosphate fertilizers, which may have high levels of radium (an element that can break down into radon).

Radon in the air breaks down quickly, giving off tiny radioactive particles. When inhaled, these particles can lodge in the lining of the lungs, where they can damage the cells. Long term exposure can lead to lung cancer. Cigarette smoking is by far the most common cause of lung cancer in the United States, but radon is the second leading cause. Scientists estimate that about 20,000 lung cancer deaths per year are related to radon. Exposure to the combination of radon gas and cigarette smoke creates a greater risk for lung cancer than either factor alone. Most radon-related lung cancers occur among smokers, but radon is also thought to cause a significant number of lung cancer deaths among non-smokers in the United States each year. Some studies have suggested that radon exposure may be linked to other types of cancer as well, but the evidence for such links has been inconsistent and not nearly as strong as it is for lung cancer.

If you are concerned about radon exposure in your home, you can read the Consumer’s Guide To Radon Reduction: How to Fix Your Home on the EPA website. If you are concerned about radon exposure in your workplace, you should consult the Occupational Safety and Health Administration  (OSHA) regulations concerning radon. OSHA has the responsibility of protecting the American workforce from unnecessary exposure to ionizing radiation, including radon.

Medical radiation

In addition to natural background radiation, there are three main sources of man-made ionizing radiation The first is medical radiation. Certain types of imaging tests, such as x-rays (including mammograms), CT scans, and nuclear medicine tests such as PET scans and bone scans expose people to low levels of radiation in order to create internal pictures of the body. MRI and ultrasound exams do not use ionizing radiation.

The increased risk of cancer from exposure to any single test is likely to be small. Still, there has been more concern in recent years as the average amount of radiation a person is exposed to from medical tests has risen. Children’s growing bodies are especially sensitive to radiation. Because of the fact that radiation exposure from all sources can add up over one’s lifetime, imaging tests that use radiation should only be done if there is a good medical reason to do so. The usefulness of the test must always be balanced against the possible risks from exposure to the radiation, and doses and techniques must be adapted for children and young adults. In some cases, other imaging tests that do not use radiation, such as ultrasound or MRI, may be an option. Because I now get imaging tests quite often, this is an issue I struggle with.

The following table gives an idea of the amount of risk for various types of exposure to ionizing radiation.

Typical Effective Radiation Dose

Exposure Effective Dose (mrem)
Average annual background exposure in the U.S. 300
Chest X-ray 10
Mammogram (2 view) 36
Dental Bitewing 0.5
DEXA (whole body 0.1
Bone Scan 440
 CT chest 700
PET procedures 700
Coast to coast Airplane roundtrip 5
Average exposure of evacuees from Belarus after 1986 Chernobyl disaster 3,100
Annual dose limit for nuclear power plant workers 5,000
Spike recorded at Fukushima Daiichi nuclear power plant 40,000 per hour
Fatal dose 1,000,000

Although the cancer risk from some medical radiation procedures seems slight, we don’t really know, since the effects take years to show up, and also because high-dose imaging only started to be used around 1980.

The Harvard Medical School has a list of precautions you can take:

  • Discuss any high-dose diagnostic imaging with your clinician. If you need a CT or nuclear scan to treat or diagnose a medical condition, the benefits usually outweigh the risks. Still, if your clinician has ordered a CT, it’s reasonable to ask what difference the result will make in how your condition is managed; for example, will it save you an invasive procedure?


  • Keep track of your radiation exposure. The President’s Panel recommended that imaging device makers indicate the radiation dose for each x-ray, and that clinicians record radiation exposures in patients’ medical records. The FDA is considering both ideas. In the meantime, you can keep track of your own x-ray history. It won’t be completely accurate because different machines deliver different amounts of radiation, and because the dose you absorb depends on your size, your weight, and the part of the body targeted by the x-ray. But you and your clinician will get a ballpark estimate of your exposure.


  • Consider a lower-dose radiation test. If your clinician recommends a CT or nuclear medicine scan, ask if another technique would work, such as a lower-dose x-ray or a test that uses no radiation, such as ultrasound (which uses high-frequency sound waves) or MRI (which relies on magnetic energy). Neither ultrasound nor MRI appears to harm DNA or increase cancer risk.


  • Consider less-frequent testing. If you’re getting regular CT scans for a chronic condition, ask your clinician if it’s possible to increase the time between scans. And if you feel the CT scans aren’t helping, discuss whether you might take a different approach, such as lower-dose imaging or observation without imaging.


  • Don’t seek out scans. Don’t ask for a CT scan just because you want to feel assured that you’ve had a “thorough checkup.” CT scans rarely produce important findings in people without relevant symptoms. And there’s a chance the scan will find something incidental, spurring additional CT scans or x-rays that add to your radiation exposure.

The American Nuclear Society has an interactive tool that you can use to compute your own radiation exposure.

You need to keep track of your own radiation exposure, and not leave the decision up to your doctors. A study involving 29,170 women with early stage (0-2b) breast cancer found that up to 60% of them received tests such as CT, bone, and PET scans that were medically unnecessary and contrary to national guidelines. The study involved 25 hospitals participating in the Michigan Breast Oncology Quality Initiative, and similar results have been found across the country. “For women newly diagnosed with early-stage breast cancer, advanced imaging is generally not medically necessary, and we know it has potential to lead to harmful side effects,” said Merry-Jennifer Markham, a medical doctor and ASCO spokesperson. Furthermore, the scans are sensitive enough to pick up small abnormalities that would never become a problem, and then they have to keep repeating the scans to make sure they haven’t grown. When I was newly diagnosed with early stage breast cancer, I was sent for CT, PET, and bone scans, without any discussion of their medical necessity.

Another source of medical radiation is radiation therapy, which is used to treat some types of cancer, including breast cancer. It can take the form of radiation that penetrates from outside the body, or of radioactive particles that are swallowed or inserted into the body. Radiation therapy involves dosages of ionizing radiation many thousand times higher than those used in diagnostic x-rays. It is intended to kill cancer cells; however, it can also lead to DNA mutations in other cells that survive the radiation, which may eventually lead to the development of a second cancer. Some studies have linked radiation therapy with an increased risk of leukemia, thyroid cancer, early-onset breast cancer, and some other cancers. The amount of increased risk depends on a number of factors, including the dose of radiation, the location in the body, and the age of the person getting it (younger people are generally at greater risk). As we have noted earlier, if cancer does develop after radiation therapy, it does not happen right away. For leukemias, most cases develop within 5 to 9 years after exposure. In contrast, other cancers often take much longer to develop. Most of these cancers are not seen for 10 years after radiation therapy, and some are diagnosed even more than 15 years later.

I looked up the dose that is typically given for radiotherapy to the breast and it was 5,000,000 mrem. According to the preceding chart, the lethal dose is 1,000,000 mrem. So why am I not dead? I could not find any explanation online, so I emailed my radiation oncologist. She explained that lethality depends not only on the dose and the time frame in which the radiation is delivered, but it also depends on the part of the body that receives the radiation. Some body parts tolerate radiation better than others, and the breast and chest wall are very tolerant. My breast received 5,000,000 mrem, but it could receive even twice that amount if there were time in between. Without any time in between, it could receive 6,000,000 or even 7,000,000 mrem, which would likely result in tissue damage that might require surgical repair, but it would not be lethal. This doesn’t completely explain the reason it is not lethal, but it is the best explanation I could get without becoming a real pest.

Some combinations of radiation therapy and chemotherapy are more risky than others. Doctors try to ensure the treatment that is given destroys the cancer while minimizing the risk that a secondary cancer will develop later on. I don’t know how my particular combination of chemotherapy and radiotherapy affected my risk, but I understand that having both is riskier than having one or the other.

Nuclear weapons and power plants

Non-medical sources of human-made ionizing radiation include nuclear weapons and nuclear power plants. The United States government conducted above-ground nuclear tests in the South Pacific and in the state of Nevada between 1945 and 1962. Military maneuvers involving about 200,000 people were conducted as part of many of these tests, which exposed these people, as well as others living in nearby areas, to different amounts of radiation. In addition, thousands of uranium miners and workers at several nuclear weapons plant sites were exposed to radiation and other toxic substances. While there is little doubt that high-dose radiation exposure can cause cancer, some issues are not as clear, such as the amount of exposure required, and the types of cancer that radiation can cause. Overall, the results of studies looking at a possible link between cancer and low-level radiation exposure have been difficult to interpret. However, the government provided financial compensation to those exposed to radiation during nuclear testing who later developed certain types of cancer or other diseases.

Survivors of the atomic bombings in Japan during World War II and the nuclear accident at Chernobyl in 1986 showed increased incidence of deaths from cancer, but since we are not able to determine which individual cancers were caused by radiation or how much radiation each person received, and we don’t have data on their nutrition and lifestyles, we don’t know exactly how high the increase was. Also, exposure in the two incidents was very different; the atomic bomb survivors received high radiation doses in a short time period, while Chernobyl survivors received lower doses over a longer period.

Studies of Chernobyl survivors show some other effects in addition to cancer. One is cataracts. Because the lens of the eye is very sensitive to ionizing radiation, cataracts can develop at doses as low as 25,000 mrem. The higher the dose, the faster the cataracts appear. My cataracts started appearing after my radiotherapy, and I wonder if that was the cause.

There was a large Russian study of emergency workers that indicated that those who had high exposures had a higher risk of death from cardiovascular disease. This is consistent with studies of radiotherapy patients who received higher doses to the heart.

People who work in nuclear power plants in the U.S. and elsewhere may be exposed to higher levels of radiation than the general public, although their exposure levels are monitored carefully. According to the Environmental Protection Agency (EPA), nuclear power plant operations account for less than one-hundredth (1/100) of a percent of the average American’s total radiation exposure.

Despite reassurances from the U.S. government that nuclear power is perfectly safe (except for occasional accidents like Three Mile Island, Chernobyl, and Fukushima), new research from the U.K. has found that the risk of breast cancer is between two and five times the normal rate for women who live within five miles downwind from nuclear reactors. Public health authorities are now getting involved to look for cancer clusters in the area.

I looked for the history of testing for the safety of nuclear power in the U.S., and found a discouraging story. The first U.S. nuclear power plant was built in 1943, to make atomic bombs, and in 1957 nuclear power was first used to generate electricity. The U.S. government declared nuclear power plants to be perfectly safe without doing any studies, and by the 1980s there were 112 nuclear power plants in the U.S. Then, in 1988, Ted Kennedy, Senator from Massachusetts, learned of an article in The Lancet describing high leukemia rates around the Pilgrim Nuclear Power Station near Boston. He notified the director of the National Institutes of Health and requested an inquiry. In 1990, the National Cancer Institute issued a report that concluded, “The survey has produced no evidence that an excess occurrence of cancer has resulted from living near nuclear facilities.” Researchers criticized the methodology, which they say used the wrong data. Then, in May 2009, the Nuclear Regulatory Commission (NRC) solicited experts to conduct a cancer study near U.S. nuclear plants, but there were so many obvious conflicts of interest that activists protested. The study was then moved to the National Academy of Science, whose National Academy Nuclear and Radiation Studies Board would direct the project. However, the board chairman and most members had strong ties to the nuclear industry and little background in the relevant science. By this time, activists had pretty much lost hope of getting any objective studies done by the government.

Meanwhile, science without ties to the nuclear industry had produced at least 60 published, peer-reviewed studies linking cancer to low-level exposure to radiation (particularly among children). Examples include a 2008 study in Germany and a 2012 study in France that both found elevated levels of child leukemia near nuclear plants, and a 2003 study in Archives of Environmental Health that found cancer rates in children that were 12.4 percent higher than nationwide occurrences in 49 counties surrounding 14 nuclear plants in the eastern U.S.

In 2013, reportedly in response to public and political pressure, the U.S. National Academy of Sciences announced that it started planning for a study of cancer risks around 104 operating nuclear reactors in 31 States and 13 fuel cycle facilities in operation in 10 States. Phase I would include six nuclear power plants: Dresden, Millstone, Oyster Creek, Haddam Neck, Big Rock Point, San Onofre and one nuclear fuel site at Erwin, Tennessee. However, the U.S Nuclear Regulatory Commission (NRC) cancelled the study in 2015, citing budgetary reasons. They felt that it would be wrong to waste the money, since they thought that the public was already sufficiently protected: “The NRC continues to find U.S. nuclear power plants comply with strict requirements that limit radiation releases from routine operations,” agency spokesman Scott Burnell wrote in defense of the decision. “The NRC and state agencies regularly analyze environmental samples from near the plants. These analyses show the releases, when they occur, are too small to cause observable increases in cancer risk near the facilities.”

In general, the government is reassuring about our exposure to ionizing radiation from nuclear energy and other human-made sources. However, it’s much more difficult for the public to independently assess the dangers from carcinogenic radiation than it is to assess the dangers from carcinogens in the environment. Since we know that neither the government nor business has been overly concerned with public safety in the case of environmental carcinogens, I personally feel a bit cynical about their reassurances concerning the safety of radiation.

Consumer products

Non-medical, human-made ionizing radiation can also come from some consumer products. Following are items that can contain enough radioactive material so that a handheld radiation survey meter can distinguish them from the general environmental background radiation: smoke detectors, watches and clocks, ceramics, glass, and compact fluorescent light bulbs.  According to the EPA, some airport security scanners use ionizing radiation and others use non-ionizing radiation,   The dose for the average American from consumer products is estimated at about 10 mrem per year.

Ionizing radiation can be used to shrink-wrap packaging, to sterilize products such as cosmetics and medical supplies, and kill germs on some foods. Some people are concerned that irradiated food may contain radiation. According to the U.S. Food and Drug Administration (FDA), irradiating food does not cause it to become radioactive and does not change nutritional value or flavor of the food. (Microwave ovens use non-ionizing electromagnetic radiation.)

Ultraviolet (UV) rays straddle the border between ionizing and nonionizing radiation. Ultraviolet rays are invisible rays that come mainly from the sun, although they can also come from man-made sources such as tanning beds and welding torches. They have more energy than visible light, but not as much as x-rays. Ultraviolet rays often have enough energy to damage the DNA in cells, which means they can cause cancer, but because they don’t have enough energy to penetrate deeply into the body, their main effect is on the skin.

Most skin cancers are a direct result of exposure to the UV rays in sunlight. Both basal cell and squamous cell cancers (the most common types of skin cancer) tend to be found on sun-exposed parts of the body, and their occurrence is related to lifetime sun exposure. The risk of melanoma, a more serious but less common type of skin cancer, is also related to sun exposure, although perhaps not as strongly. While UV rays make up only a tiny fraction of the sun’s wavelengths, they are mainly responsible for the damaging effects of the sun on the skin. Oddly, many skin cancers are treated with radiotherapy.

In addition to skin cancer, prolonged exposure to UV radiation from the sun may cause degenerative changes in cells of the skin, fibrous tissue, and blood vessels. This damage can lead to premature skin aging, photodermatoses, actinic keratosis, inflammatory reaction of the eye, and cataracts.

While large amounts of UV radiation is dangerous, small amounts of can be beneficial for people. UV radiation is used to treat several diseases, including rickets, psoriasis, eczema and jaundice. Also, the body needs UV radiation to produce Vitamin D. The World Health Organization (WHO) recommends 5 to 15 minutes of casual sun exposure of hands, face and arms two to three times a week during the summer months.

Non-ionizing radiation

 Non-ionizing radiation is electromagnetic radiation that does not have enough energy to remove electrons from atoms. It does not directly damage DNA, but it might be able to affect cells in other ways. Common types of non-ionizing radiation include some ultraviolet (UV) rays, visible light, infrared rays, microwaves, radiofrequency rays (radio and television), and extremely low frequency (ELF) and electromagnetic field (EMF) rays. Non-ionizing radiation is produced by a wide variety of products in the home and in the workplace. Concerns have been raised about a possible link between some types of non-ionizing radiation and cancer, but the way this link would work is not clear.

Electric currents create extremely low-frequency (ELF) electromagnetic fields (EMF), which are at the low-energy end of the electromagnetic spectrum. We are all exposed to electromagnetic fields from the earth itself and from man-made sources. Examples of man-made sources include power lines, household wiring, and electrical appliances. Some epidemiological studies have suggested increased cancer risk associated with magnetic field exposures near electric power lines. One of the main concerns has been whether ELF affects the risk of childhood cancers such as leukemia and brain tumors. The National Institute of Environmental Health Sciences (NIEHS) has advised that people concerned about EMF exposure may want to consider practical ways to reduce their exposure, such as finding out where their major EMF sources are and limiting the time spent near them.

Modern television and computer screens give off several kinds of radiation, most of which is in the extremely low frequency (ELF) range. Concerns have been raised about possible health problems associated with the use of these screens, including cancer and birth defects. The amount of energy given off by these screens is far below government exposure standards, and at this time the American Cancer Society says that available evidence does not support links to either of these health problems. Research in this area continues.

Cell phones and cell phone towers use radiofrequency and low-level microwave radiation to transmit and receive signals. Neither cell phones nor cell towers have been conclusively linked to increased risks of cancer, but most researchers and government agencies agree that more research on cell phones is needed, especially with regard to long-term use and use among children. According to the American Cancer Society (ACS): “Studies thus far have not shown a consistent link between cell phone use and cancers of the brain, nerves, or other tissues of the head or neck. More research is needed because cell phone technology and how people use cell phones have been changing rapidly.”

Radiofrequency radiation is also emitted from radio and television broadcast transmitters, citizen band radios, electric heaters, WiFi routers, computers, printers, and other devices that allow wireless connection to the internet and computer networks. These devices operate within the frequency range of cell phones systems, but use much less power. However, the effects of all radiation are cumulative, and when they reach adulthood, today’s children will have a much higher exposure to RF.

Microwaves have energy levels in between radio waves and infrared waves. Like other forms of non-ionizing radiation, they do not have enough energy to directly damage DNA. Microwave radiation is used in microwave ovens and radar equipment, and cell phones may also use some low-energy microwaves. Microwave ovens work by using very high levels of microwaves to heat foods. Exposure to high levels of microwaves can have effects on health, but the small amount that can leak from a microwave oven is not considered dangerous. Mainstream sources seem to consider microwaved food to be safe, but there is some evidence to the contrary. For example, it was found that the nonstick coating inside microwaved popcorn bags can decompose and produce perfluorooctanoic acid, a chemical that has been associated with increased risk of certain cancers, including liver and prostate cancer. I think it likely that other types of packaging for processed microwaveable food could also release chemicals that might be carcinogenic or unhealthy in other ways.

Most forms of radar use waves in the microwave range. Questions have been raised about exposure to radar and the risk of developing cancer, such as in police officers who use radar guns in traffic enforcement. I was not able to find any studies more recent than that one that OSHA did in 1995, which had inconclusive results.

When we assess our risk of cancer, it is important to consider that all the risk factors, whether from lifestyle, genetics, or exposure to all the different kinds of carcinogens, are interactive and cumulative. Since we are continually bombarded with carcinogens that cannot be avoided, we each have to decide which things are in our control and where we are willing to draw our lines.


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