Cellular (cell) phones first became widely available in the United States in the 1990s, but their use has increased dramatically since then. According to the Cellular Telecommunications & Internet Association, there were an estimated 270 million cell phone subscribers in the United States as of December 2008, representing about 87% of the total population.

Based on the large and still growing number of cell phone users (both adults and children), and the fact that cell phones give off radio-frequency (RF) waves, some concerns have been raised about the safety of cell phone use. With respect to cancer, concern focuses on whether cell phones might increase the risk of brain tumors or other tumors in the head and neck area.

How do cell phones work?

Cell phones communicate with nearby cell towers through RF waves, a form of energy located on the electromagnetic spectrum between FM radio waves and microwaves. Like FM radio waves, microwaves, visible light, and heat, they are a form of non-ionizing radiation. They cannot cause cancer by directly damaging DNA. RF waves are different from stronger types of radiation such as x-rays, gamma rays, and ultraviolet (UV) light, which can break the chemical bonds in DNA.

At very high levels, RF waves can heat up body tissues. (This is the basis for how microwave ovens work.) But the levels of energy given off by cell phones are much lower, and the warmth from a cell phone does not damage body tissues.

How are people exposed?

The RF waves from cell phones come from the antenna, which is part of the body of a hand-held phone. The waves are strongest at the antenna and lose energy as they travel away from the phone. The phone is typically held against the side of the head when in use. The closer the antenna is to the head, the greater a person's expected exposure to RF energy.

Many factors can affect the amount of RF energy to which a person is exposed, including:

• The amount of time the person is on the phone
• The model of phone being used: different phones give off different amounts of energy
• Whether or not the person is using a hands-free device
• The distance and path to the nearest cell phone tower: being farther away from the tower requires more energy to get a good signal, as does being inside a building
• The amount of cell phone traffic in the area at the time

Other factors may also affect exposure. For example, older cell phones (analog models) used more energy than newer, digital phones.

The amount of RF energy absorbed from the phone into the user's local tissues is known as the specific absorption rate (SAR). Different cell phones have different SAR levels. Cell phone makers are required to report the SAR level of their product to the Federal Communications Commission (FCC). This information is sometimes listed inside the battery compartment on the phone. The upper limit of SAR allowed in the United States is 1.6 watts per kilogram (W/kg) of body weight.

Do cell phones cause tumors?

Because cell phones are held near the head when in use, the main concern has been over whether they might cause or contribute to tumors in this area, including:

• Malignant (cancerous) brain tumors such as gliomas
• Non-cancerous tumors of the brain such as meningiomas
• Non-cancerous tumors of the nerve connecting the brain to the ear (acoustic neuromas)
• Non-cancerous tumors of the salivary glands

What do studies in humans suggest?

About 30 studies have looked at possible links between cell phone use and tumors. Most of these studies have focused on brain tumors. Many of these have been case-control studies, in which patients with brain tumors (cases) were compared to people free of brain tumors (controls), in terms of their past use of cell phones.

In general, these studies have yielded similar results:

• Patients with brain tumors do not report more cell phone use overall than the controls. This finding is true when all brain tumors are considered as a group, when specific types of tumors are considered, and when specific locations within the brain are considered. In fact, most of the studies show a trend toward a lower risk of brain tumors among cell phone uses, for unclear reasons.

• Most studies do not show a "dose-response relationship" -- a tendency for the risk of brain tumors to increase with increasing cell phone use, which would be expected if cell phone use caused brain tumors.

• Several studies published by the same research group in Sweden report increased risk of tumors on the side of the head where the cell phone was held, particularly with 10 or more years of use. It is hard to know what to make of these findings because studies by other researchers have not had the same results, and there is no overall increase in brain cancer in Sweden during the years that correspond to these reports.

A large, long-term study following more than 420,000 cell phone users in Denmark between 1982 and 2002 had findings similar to those of the case-control studies. Cell phone use, even for more than 10 years, was not linked with an increased risk of brain tumors or cancer overall, nor was there a link with any brain tumor subtypes or with tumors in any location within the brain. As in the case-control studies, no link was found between brain tumor risk and length of cell phone use, age when a person started using the phone, or type of cell phone used.

Taken as a whole, most studies to date have not found a link between cell phone use and the development of tumors. However, these studies have had some important limitations.

First, studies have not yet been able to follow people for very long periods of time. When tumors form after a known cancer-causing exposure, it usually takes decades for them to develop. Because cell phones have been in widespread use for less than 20 years in most countries, it is not possible to rule out future health effects that have not yet appeared.

Second, the studies done so far have focused on adults, not children. Cell phone use is now widespread even among young children. It is possible that if there are health effects, they might be more pronounced in children because their nervous systems are still developing and their lifetime exposure will be greater than adults, who started at a later age.

Third, the measurement of cell phone use in most studies has been crude. Most have been case-control studies. These types of studies have relied on people's memories for information about past cell phone usage, which may or may not be dependable.

Further research is needed to address these limitations. Several large studies now under way, including the 13-country INTERPHONE study, should help provide clearer answers in the near future.

What does the laboratory evidence suggest?

As noted above, the RF waves given off by cell phones don't have enough energy to damage DNA directly. Because of this, many scientists believe that cell phones aren't able to cause cancer. Most studies done in the lab have supported this theory, finding that RF waves do not cause DNA damage.

A number of scientists have reported that the RF waves from cell phones produce effects in human cells (in lab dishes) that might possibly help tumors grow. However, several studies in rats and mice have looked at whether RF energy might promote the development of tumors caused by other known carcinogens (cancer-causing agents). These studies did not find evidence of tumor promotion. Given the widespread use of cell phones, it is important that all reasonable claims be carefully tested by other scientists with expertise in this area.

What do expert agencies say?

In general, expert agencies agree that most evidence to date does not point to cell phone use increasing the risk of tumors, but that more research is needed to look at possible long-term effects.

According to the Food and Drug Administration (FDA), which regulates the safety of radiation-emitting devices such as cell phones in the United States:

The majority of studies published have failed to show an association between exposure to radiofrequency from a cell phone and health problems.

According to the Federal Communications Commission (FCC):

There is no scientific evidence that proves that wireless phone usage can lead to cancer or a variety of other problems, including headaches, dizziness or memory loss. However, organizations in the United States and overseas are sponsoring research and investigating claims of possible health effects related to the use of wireless telephones.

According to the Centers for Disease Control and Prevention (CDC):

Although some studies have raised concerns, the scientific research, when taken together, does not indicate a significant association between cell phone use and health effects.

According to the National Toxicology Program (NTP), which is currently conducting studies of the possible health effects of cell phones:

While the weight of the current scientific evidence has not conclusively linked cell phones with any health problems, the NTP and other scientific organizations conclude that additional data are needed.

According to the National Cancer Institute (NCI):

Although research has not consistently demonstrated a link between cellular telephone use and cancer, scientists still caution that further surveillance is needed before conclusions can be drawn.

The United States Environmental Protection Agency (EPA), National Toxicology Program (NTP), and the International Agency for Research on Cancer (IARC), 3 of the main agencies that classify cancer-causing exposures (carcinogens), have not classified cell phones as to their cancer-causing potential.

Do cell phones cause any other health problems?

Few other health concerns have been raised about cell phone use. One has been whether the RF waves from cell phones might interfere with medical devices such as heart pacemakers. According to the FDA, cell phones should not pose a major risk for the vast majority of pacemaker wearers. Still, people with pacemakers may want to take some simple precautions to help ensure that their cell phones don't cause a problem, such as not putting the phone in a shirt pocket close to the pacemaker.

Several studies have found that people who use cell phones while driving are more likely to be in car accidents. It is not clear that hands-free phones are any safer than hand-held phones when it comes to driving.

Can I lower my exposure to RF waves from cell phones?

Studies now under way should give a clearer picture of the possible health effects of cell phone use in the future. Until then, there are several things that people who are concerned about RF waves can do to limit their exposure.

Use a hands-free device such as a corded or cordless earpiece. Using an earpiece moves the antenna away from the user's head, which decreases the amount of RF waves that reach the head. Corded earpieces emit virtually 0 RF waves (although the phone itself still emits small amounts of RF waves that can reach parts of the body if close enough, such as on the waist or in a pocket). Bluetooth^® earpieces have an SAR value of around 0.001 watts/kg (less than one thousandth the SAR limit for cell phones as set by the FDA and FCC).

Choose a phone with a low SAR value. Different models of phones can give off different levels of RF waves. One way to get information on the SAR level for a specific phone model is to find the FCC identification (ID) number for that model. The FCC ID number is usually somewhere on the phone, sometimes under the battery pack. Once you have the ID number, go to the following Web address: www.fcc.gov/oet/ea/fccid. On this page, you will see instructions for entering the FCC ID number.

Limit your (and your children's) cell phone use. One of the most obvious ways to limit exposure to RF waves from cell phones is to limit how much you use them. You may want to use your cell phone only for shorter conversations, or use it only when a conventional phone is not available. Parents who are concerned about their children's exposure may limit how much time they spend on the phone.

For safety reasons, it is especially important to limit or avoid the use of cell phones while driving.

What about cordless phones?

Cordless phones, commonly used in homes, have base units that are plugged into telephone jacks and wired to a local telephone service. They are not considered "cell" phones. The question of health risks from cordless phones, which operate at about 1/600 the power of cell phones, has not been raised.

Additional resources

National organizations and Web sites*

In addition to the American Cancer Society, other sources of patient information and support include:

Federal Communications Commission
RF Safety Program, Office of Engineering and Technology
Web site: www.fcc.gov/oet/rfsafety/

Food and Drug Administration
Radiation-Emitting Products: Cell Phones
Web site: www.fda.gov/Radiation-EmittingProducts/RadiationEmittingProductsandProcedures/HomeBusinessandEntertainment/CellPhones/default.htm

National Cancer Institute
Cellular Telephone Use and Cancer Risk
Web site: www.cancer.gov/cancertopics/factsheet/Risk/cellphones

National Institute of Environmental Health Sciences
Electric and Magnetic Fields
Web site: www.niehs.nih.gov/health/topics/agents/emf/index.cfm

* Inclusion on this list does not imply endorsement by the American Cancer Society.

The American Cancer Society is happy to address almost any cancer-related topic. If you have any more questions, please call us at 1-800-227-2345 at any time, 24 hours a day.

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Last Medical Review: 01/05/2010
Last Revised: 01/05/2010