There are three main reasons why people are concerned that cellular telephones (also known as "wireless" or "mobile" telephones) may cause certain types of cancer:

• Cellular telephones emit radiofrequency (RF) energy (radio waves), which is a form of radiation that is under investigation for its effects on the human body.
• Cellular telephone technology emerged in Europe in the 1980s but did not come into widespread use in the United States until the 1990s. The technology is rapidly changing, so there are few long-term studies of the effects of RF energy from cellular telephones on the human body.
• The number of cellular telephone users has increased rapidly. As of December 2008, there were more than 270 million subscribers to cellular telephone service in the United States, according to the Cellular Telecommunications and Internet Association. This is an increase from 110 million users in 2000 and 208 million users in 2005.

For these reasons, it is important to learn whether RF energy from cellular telephones affects human health.

This answer from the National Cancer Institute has been reviewed and/or edited by Dr. William D. Knopf.