What level of RF is dangerous?

What is radiofrequency (RF) radiation?
Radiation is the emission (sending out) of energy from any source. X-rays are an example of radiation, but so is the light that comes from the sun and the heat that is constantly coming off our bodies.

When talking about radiation and cancer, many people think of specific kinds of radiation such as x-rays or the radiation made by nuclear reactors. But there are other types of radiation that act differently.

Radiation exists across a spectrum from very high-energy (high-frequency) radiation to very low-energy (low-frequency) radiation. This is sometimes referred to as the electromagnetic spectrum.

Examples of high-energy radiation include x-rays and gamma rays. They, as well as some higher energy UV radiation, are called ionizing radiation, which means they have enough energy to remove an electron from (ionize) an atom or molecule. This can damage the DNA inside of cells, which can result in cancer.

Radiofrequency (RF) radiation, which includes radio waves and microwaves, is at the low-energy end of the electromagnetic spectrum. It is a type of non-ionizing radiation. Non-ionizing radiation has enough energy to move atoms in a molecule around or cause them to vibrate, but not enough to ionize (remove charged particles such as electrons). 

RF radiation has lower energy than some other types of non-ionizing radiation, like visible light and infrared, but it has higher energy than extremely low-frequency (ELF) radiation.

If RF radiation is absorbed in large enough amounts by materials containing water, such as food, fluids, and body tissues, it can produce heat. This can lead to burns and tissue damage. Although RF radiation does not cause cancer by damaging DNA in cells the way ionizing radiation does, there has been concern that some forms of non-ionizing radiation might have biological effects that could result in cancer in some circumstances.

How are people exposed to RF radiation?
People can be exposed to RF radiation from both natural and man-made sources.

Natural sources include:

*Outer space and the sun
*The sky – including lightning strikes
*The earth itself – most radiation from the earth is infrared, but a tiny fraction is RF
*Man-made RF radiation is used for many different things, such as

Broadcasting radio and television signals
*Transmitting signals from cordless telephones, cell phones and cell phone towers, satellite phones, and 2-way radios
*Radar
*WiFi and Bluetooth
*Cooking food (in a microwave oven)
*Heating body tissues to destroy them in medical procedures
*“Welding” pieces of polyvinyl chloride (PVC) using certain machines
*Millimeter wave scanners (a type of full body scanner used for security screening)

Some people can have significant RF exposure as part of their jobs. This includes PVC welders, people who maintain antenna towers that broadcast communication signals, and people who use or maintain radar equipment.

Most people are exposed to much lower levels of man-made RF radiation every day due to the presence of RF signals all around us. They come from radio and television broadcasts, WiFi and Bluetooth, cell phones (and cell phone towers), and other sources.

Microwave ovens
Microwave ovens work by using very high levels of a certain frequency of RF radiation (in the microwave spectrum) to heat foods. When microwaves are absorbed by food containing water, it causes the water molecules to vibrate, which produces heat. Microwaves do not use x-rays or gamma rays, and they do not make food radioactive. Microwave ovens can cook food, but they do not otherwise change the chemical or molecular structure of it.

Microwave ovens are designed so that the microwaves are contained within the oven itself. The oven only makes microwaves when the door is shut and the oven is turned on. When microwave ovens are used according to instructions, there is no evidence that they pose a health risk to people. 

In the US, federal standards limit the amount of radiation that can leak from a microwave oven to a level far below what would harm people. Ovens that are damaged or modified, however, could allow microwaves to leak out, and so could pose a hazard to people nearby by potentially causing burns.

Although some people have been injured from microwave ovens, most often they have been burns from contact with steam or hot food.

Full-body security scanners
In many airports in the United States, the Transportation Security Administration (TSA) uses full body scanners to screen passengers. The scanners currently used by the TSA use millimeter wave imaging. 

These scanners send out a small amount of millimeter wave radiation (a type of RF radiation) toward the person in the scanner. The RF radiation passes through clothing and bounces off the person’s skin as well as any objects under the clothes. The radiation is sensed by receivers that create images of the person.

Millimeter wave scanners do not use x-rays (or any other kind of high-energy radiation) and the amount of RF radiation used is very low. According to the US Food and Drug Administration (FDA), these scanners have no known health effects. However, TSA often allows people to be screened in a different way if they object to screening with these scanners.

Cell phones and cell phone towers
Cell phones and cell phone towers use RF radiation to transmit and receive signals. Some concerns have been raised that these signals might increase the risk of cancer, and research in this area continues. For more detailed information, see Cellular Phones and Cellular Phone Towers.

Does RF radiation cause cancer?
Researchers use 2 main types of studies to try to determine if something might cause cancer.

Lab studies: 

In studies done in the lab, animals are exposed to a chemical or physical agent (such as RF energy) to see if it causes tumors or other health problems.

Researchers might also expose normal human cells in a lab dish to see if it causes the types of changes that are seen in cancer cells. It’s not always clear if the results from these types of studies will apply to humans, but lab studies allow researchers to carefully control for other factors that might affect the results and to answer some basic science questions.

Studies in people: 

Another type of study looks at cancer rates in different groups of people. Such a study might compare the cancer rate in a group exposed to something like RF energy to the rate in a group not exposed to it, or compare it to what the expected cancer rate would be in the general population. But sometimes it can be hard to know what the results of these studies mean, because many other factors might affect the results.

Often neither type of study provides enough evidence on its own, so researchers usually look at both lab-based and human studies when trying to figure out if something causes cancer.

Studies done in the lab
Most lab studies done so far have supported the idea that RF waves don't have enough energy to damage DNA directly. Because of this, it’s not clear how RF radiation might be able to cause cancer.

A few studies have reported evidence of biological effects that could be linked to cancer, but this is still an area of research.

A study by the US National Toxicology Program (NTP) exposed large groups of lab rats and mice to types of RF energy used in cell phones. The animals were exposed over their entire bodies for about 9 hours a day, starting before birth and continuing for up to 2 years. 

The study found an increased risk of rare heart tumors called malignant schwannomas in the male rats exposed to RF radiation, as well as possible increased risks of certain types of tumors in the brain and adrenal glands. However, there was no clear increased risk among female rats or among male or female mice in the study. The male rats also lived longer than rats who were not exposed to RF radiation, for unclear reasons. 

Some aspects of this study make it hard to know what these results might mean for people, but the results add evidence to the idea that RF radiation might potentially impact human health.

Studies in people
Studies of people who may have been exposed to RF radiation at their jobs (such as people who work around or with radar equipment, those who service communication antennae, and radio operators) have found no clear increase in cancer risk.

A number of studies have looked at the possible link between cell phones and cancer. Although some studies have shown a possible link, many others have not. The possible link between cell phones and cancer is hard to study for many reasons, including the relatively short time that cell phones have been in widespread use, changes in the technology over time, and difficulty in estimating each person’s exposure. The possible link between cell phones and cancer risk is discussed in detail in Cellular Phones.

What do expert agencies say?
Several national and international agencies study exposures and substances in the environment to determine if they can cause cancer. (An exposure or substance that causes cancer or helps cancer grow is called a carcinogen.) The American Cancer Society looks to these organizations to evaluate the risks based on evidence from laboratory, animal, and human research studies.

The International Agency for Research on Cancer (IARC) is part of the World Health Organization. One of its goals is to identify causes of cancer. IARC has stated that there is limited evidence that RF radiation causes cancer in animals and humans, and classifies RF radiation as “possibly carcinogenic to humans” (Group 2B). 

This was based on the finding of a possible link in at least one study between cell phone use and a specific type of brain tumor. IARC considers the evidence overall to be “limited” because of the conflicting findings and methodologic limitations in some of the studies.

The other main agencies that classify cancer-causing exposures (carcinogens), including the US Environmental Protection Agency (EPA) and the US National Toxicology Program (NTP), have not formally classified RF radiation as to its cancer-causing potential.

Does RF radiation cause any other health problems?
Studies in the lab
In animals, the main effects of exposure to RF are related to heating (sometimes called thermal effects). High doses of RF radiation can raise body temperature, even to the point of being fatal. Focusing RF radiation on one area of the body can lead to burns and the breakdown of tissue. When RF waves are focused on the eye, it can cause cataracts to form.

It isn’t clear what effects, if any, RF radiation has at levels of exposure too low to produce heating.

In people
High doses of RF radiation can cause injuries through heating. For example, some people accidentally exposed to large amounts of RF radiation from radar equipment have developed severe burns. But it’s not clear if exposure to lower levels of RF radiation, even over long periods of time, can have harmful health effects.

People who are near microwave radar equipment can be exposed to enough pulsed microwave radiation (a type of RF radiation) that they begin to hear clicking noises. This is sometimes called RF hearing and does not seem to cause long term health problems.

Although there is concern that people exposed to low levels of microwaves over long periods of time in their jobs could have an increased risk of cataracts or loss of fertility (in men), this has not been seen in large studies.

How can I avoid exposure to RF radiation?
Because sources of RF radiation are so common in the modern environment, there is no way to completely avoid exposure to it. It may be possible to lower your exposure to RF radiation by avoiding jobs with increased RF exposure, keeping away from appliances and equipment that use RF, and using devices that allow mobile phones to be used without placing them against the ear. Still, it isn’t clear that doing so will be helpful in terms of health risks.

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