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Environmental Health
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The term ‘radiation’ strikes fear in the hearts of many people. It conjures up images of nuclear reactors and atomic bombs and triggers thoughts of cancer and birth defects. In fact, radiation is far more common—and less dangerous—than most people imagine. It can be found almost everywhere in our environment. It’s in the soil we walk on, and it radiates down on us from the sun; it comes at us from our television sets and computer screens, and it helps light our homes and cook our meals.

Radiation is a form of energy. Visible light that comes from a lamp and radio waves that are emitted from a radio are two types of radiation. Other types of radiation include microwaves, radio waves, ultraviolet light, and infrared.

Ionizing radiation is the most energetic form of radiation. X-rays are perhaps the best known type of ionizing radiation; other types include alpha, beta and gamma rays. (Alpha, beta, and gamma rays are emitted from radioactive materials.) Ionizing radiation is naturally present in our environment and exposure to certain levels of it can’t be avoided. In fact, approximately 80 percent of all exposure can be attributed to naturally-occurring sources.

Radon is the largest source of natural radiation exposure. Radon gas is produced by the decay of uranium, an element almost universally present in soil and rock. The gas moves slowly through the ground and can enter homes and contaminate indoor air. Radon, however, is not the only source of natural radioactivity. Ionizing radiation also comes to us from outer space, and from other radioactive elements in the earth’s crust.

Levels of natural radiation vary greatly from one location to the next. People living at high altitude, for example, are exposed to greater amounts of cosmic radiation (radiation from outer space) than those living at lower altitudes; individuals living in regions where the soil is rich in uranium are exposed to more radon than those living in areas with lower levels of this element in the soil.

Only about 20 percent of exposure to ionizing radiation comes from man-made sources. Medical procedures, like diagnostic x-rays and radiation therapy, are the most significant contributors. But some consumer products, such as smoke detectors and televisions, also give off low levels of it. Individuals who smoke are exposed to ionizing radiation in tobacco smoke.

Some individuals are exposed to ionizing radiation in their work environment. X-ray technicians and individuals working in research laboratories, for example, have the potential for being exposed to significant levels of radiation on the job. By law, individuals with occupational exposure to radiation must be carefully monitored.

While any exposure to ionizing radiation can be potentially dangerous, it’s believed that the body is able to successfully defend itself against and repair the damaging effects of low level exposures. Exposure to higher levels, however, can be harmful. In adequate doses, ionizing radiation can damage or alter the genetic code, or DNA, of cells that are exposed to it.

Large doses can clearly cause certain types of cancer, including leukemia and cancer of the thyroid, skin, breast, and lung. In high doses, radiation can also damage the body’s immune system and cause cataracts. Ionizing radiation can cause genetic defects in children whose parents were exposed to large doses of it. (Radiation damages the genetic material in their reproductive cells which is then passed on to their offspring.) Fetal tissue seems to be particularly sensitive to the effects of radiation, and babies exposed to radiation in-utero are at risk for developmental problems.

Acute radiation syndrome, or radiation sickness, can develop in individuals exposed to very high doses of radiation over a short period of time, such as atomic bomb survivors and patients receiving radiation therapy. Overwhelming damage to tissues and organs throughout the body causes symptoms ranging from vomiting and diarrhea to seizures and even death.

Non-ionizing radiation has not been linked to adverse health consequences the way ionizing radiation has. However, the relative safety of these forms of radiation continues to be debated.

Non-ionizing radiation is emitted from a wide range of electric appliances including televisions, hair dryers, electric blankets, computers, and microwaves. Although most experts believe that levels given off by these sources are unlikely to be problematic, there’s some evidence suggesting a link with cancer.

Perhaps the greatest controversy surrounding the health effects of non-ionizing radiation involves cellular phones. In recent years, there has been concern that cellular phones and cell phone towers—which emit non-ionizing radiation to transmit and receive signals—can cause brain tumors. Thus far, studies have not found a consistent association between cell phone use and cancer. However, additional studies are being conducted to further explore this issue.


Ultraviolet Radiation FAQ pdf icon (Los Angeles County Department of Public Health)
Los Angeles County Department of Public Health (Radiation Management Program)
MedlinePlus for Radiation Exposure (U.S. National Library of Medicine and National Institutes of Health)
Radiation Topics (U.S. Environmental Protection Agency)

Cellular Phones
Cell Phones and Cancer Risk (National Cancer Institute)
Cell Phones (U.S. Food and Drug Administration)

Electromagnetic (EMF) Radiation
Electromagnetic Fields (World Health Organization)
Electric and Magnetic Fields (EMF) Radiation from Power Lines (U.S. Environmental Protection Agency)

Microwave Ovens
Microwave Oven Radiation (U.S. Food and Drug Administration)

We Want You to Know About Television Radiation (U.S. Food and Drug Administration)


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Director of Environmental Health
Liza Frias
Public Health has made reasonable efforts to provide accurate translation. However, no computerized translation is perfect and is not intended to replace traditional translation methods. If questions arise concerning the accuracy of the information, please refer to the English edition of the website, which is the official version.
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