The World Health Organization's International Agency for Research on Cancer says low-level radiation from cell phones and other wireless devices may cause cancer.
A 2010 study showed those who used cell phones for more than 10 years had double the rate of glioma, a rare type of brain tumor.
Researchers noted the evidence is not conclusive. There are also no studies on cell phone's long-term use on children, who have thinner skulls and are more susceptible to radiation.
"A lot more research needs to be done. Science is very slow on these matters. It took decades to move from cigarettes 'may cause harm' to cigarettes actually 'cause harm,'" Dr. Joel Moskowitz, with the University of California Berkeley, said.
Still, the WHO and the American Cancer Society are warning people that it is important to take practical steps to reduce radiation exposure.
Meanwhile, the cellphone industry has been quick to point out that the WHO did not conduct any new research. They also noted that the organization has also at one time classified pickled vegetables and coffee as possible carcinogens.
But that is little comfort to Ellie Marks, who believes 20 years of cell phone use caused her husband's brain cancer.
"Had he known, he never would have held it directly to his head. He wouldn't be dying from brain cancer," she said.
Currently, experts aren't recommending consumers stop using cell phones. But the American Cancer Society does suggest using headsets or the speaker phone option on your phone.