Radiofrequency electromagnetic fields (RF or wireless) have been designated as a carcinogen by the World Health Organization's International Association for Research on Cancer, alongside lead, DDT, and asbestos. Within 1,000 feet of a cell tower, studies show a substantial risk to human and environmental health. RF radiation is completely invisible to humans, but it can cause cancer and other health problems. Cell phones use radio waves to communicate with cellular towers, which then relay that information to another cell phone. As you use your cell phone, it generates radio waves that are detectable by others nearby. These other people have the same ability to detect radio waves as we do with our eyesight: using special equipment they can see whether your phone is on or not, and if it is turned on they can also see what type of signal it is transmitting. The biological effects of RF radiation are largely dependent on its intensity and duration. The closer you are to a cell tower, the more energy will be transmitted into your body. This energy can cause cancerous tumors to form if it is intense enough or over a long period of time. However many studies show that the risks of RF radiation are greatly exaggerated, and some researchers believe that the fears surrounding cell phone usage may be unwarranted. It is best to keep mobile phone transmissions away from bodies because this allows the body to absorb less of the radiation.