Cell phones. You can’t live without them, but can you live—and stay healthy—with them?

This week the question gained new urgency when Berkeley, California became the first city to pass an ordinance banning phone retailers from selling their products without a warning about potential exposure to radiation. At least six other states have tried to pass a “Right to Know,” bill like this one, which will require a message be attached to each phone with language such as:

“If you carry or use your phone in a pants or shirt pocket or tucked into a bra when the phone is on and connected to a wireless network, you may exceed the federal guidelines for exposure to RF [radio frequency] radiation. This potential risk is greater for children. Refer to the instructions in your phone or user manual for information about how to use your phone safely."

The legislation is inspired by guidelines from the Federal Communications Commission, which outline specific distances at which different phones should be held away from the body to protect against exposure to radiofrequency energy (for iPhones, they recommend at least 15 mm away).

Berkeley’s new measure comes on the heels of another big development in the cell phone world—a collective international appeal sent to the United Nations and World Health Organization by over 190 scientists around the world urging for the formation of protective guidelines informing of the dangerous effects of non-ionizing radiation present in cell phones, Wi-Fi, broadcast antennas, and even baby monitors. Their overall concern is that the non-ionizing electromagnetic fields of cell phones can potentially result in various forms of brain tumors. In 2011, the World Health Organization officially classified mobile phone use as a potential “carcinogenic hazard.”

While public health guidelines can be useful and should certainly be pursued, there is actually little evidence to support conclusively that cell phones result in brain tumors.

The largest international study to date of brain tumor risk in cell phone usage was published in 2010 by the Interphone study group. In it, the researchers found no risk of two brain tumor types—glioma and meningioma—in relation to cell phone use. In fact, a reduced risk of both glioma and meningioma was surprisingly found in regular cell phone users, though those at the highest exposure levels did show some increase in glioma risk. The authors noted that evidence of increased glioma risk in users with the highest cell phone usage was inconclusive due to possible biases in the way data was collected.

A different multi-center study published last year also uncovered no brain tumor risk with cell phone usage when comparing regular users and non-users. They did find, however, that heavy cell phone use with the highest life-long cumulative duration and number of calls was correlated with an increased risk of glioma and meningioma, though the study was again subject to recall bias. The authors admitted it was possible some participants who were classified as the heaviest users over-reported their cell phone usage.

Prior studies analyzing cell phone usage and brain cancer largely focused on adults. The dramatic rise in cell phone ownership in children in the last five years begs the question of whether children—with their thinner skull bone and developing brain—are more susceptible to brain cancer from the non-ionizing electromagnetic fields emitted from cell phones.

The truth is that there are conflicting studies on the issue.

A multi-center study conducted in Denmark, Sweden, Norway, and Switzerland on children between 7 and 19 years old found no evidence of brain tumor risk from cell phones. Another study limited to Sweden advised precaution, as a higher risk for glioma was seen in participants who started using cell phones as children or adolescents.

Given the studies available on both adults and children, no definitive causal association can be made between cell phones and brain cancer. Despite the Federal Communications Commission (FCC) specific guidelines limiting the amount of RF energy that can be emitted by manufactured wireless devices, it notes the current lack of scientific evidence to link cell phones and cancer—and does not endorse the need for precautions to limit exposure.

As cell phones become better and “smarter” thanks to rapid technological advances, many users are finding themselves more dependent than ever on their cellular devices. The Pew Research Center’s Internet & American Life Project found that cell phone ownership surpassed 90 percent of all adults for the first time in 2013.

If the contradictions prove anything, it’s that we need to continue to study the possible effects of non-ionizing electromagnetic fields on brain cancer. Given the ubiquitous use of cell phones, international guidelines on cell phone usage can even prove useful and informative to the public. But can we definitively say that cell phones cause brain cancer? Absolutely not. Should we study the effects of non-ionizing radiation on the body, specifically the brain and in children? Absolutely.