There are two types of electromagnetic radiation:
Ionizing – high frequency and high energy (x-rays, cosmic rays, etc.
Non-ionizing – low frequency and low energy (radio frequency, power frequency, etc.)
Cell phones transmit a form of non-ionizing radiation from their antennas. This transmittance is how wireless calls and WiFi connections occur. Body tissues close to it absorb this energy. (1)
The radiation is increased during active phone calls, but the exposure continues long afterward. A study was published in 2009 that measured the pelvic bone density in 150 men, all of whom wore their phones attached to their belt for 15 hours a day for about six years. The scientists found the bone mineral density was decreased on the side of the pelvis where the cell was carried.
In one case, a woman with no predisposition for cancer became afflicted with multi-focal breast cancer. Her cancer specialists connected the dots, and the pattern and distribution of the cancerous cells outlined the shape of her cell phone. This seemed peculiar enough; then the woman explained that she is continuously tucking her phone into her bra.