As you read this story, is your cell phone in your pocket or purse, on your desk beside you, or even in your hand?
On a planet of 6.8 billion people, about 5 billion use cell phones. But could radiation from those phones be harmful to your health?
In her new book, "Disconnect: The Truth About Cell Phone Radiation, What the Industry Has Done to Hide It, and How to Protect Your Family," Devra Davis, an environmental health scientist formerly with the National Academy of Sciences, says the answer is a resounding yes.
Over the years, scientists and public health officials have explored the effects of mobile phone radiation on human health.
Time and again, they've said that while more research is needed to examine potential long-term effects, fears of cell phones are mostly unfounded.
The American Cancer Society says most published studies have not found a link between cell phones and the development of tumors. The Food and Drug Administration says "the weight of scientific evidence has not linked cell phones with any health problems."
But Davis, who says she was once a skeptic herself, argues that compelling evidence to the contrary exists in research institutions around the world.
"Disconnect" resurrects decades-old studies on the topic and probes new research to build a case for why cell phone radiation is now a "national emergency."
ABCNews.com spoke with Davis about her cell phone "expose." Here's an edited version of our conversation.
You've previously written about environmental pollution and public health impacts ("When Smoke Ran Like Water" and "The Secret History of the War on Cancer"). Why did you decide to turn your attention to cell phones?
"What I'm really concerned about here and why I wrote this book is because there's a lot of really compelling experimental evidence on the effect of electromagnetic fields on cells. … I'm an epidemiologist but I'm also a toxicologist, so that means I study patterns of disease in animals and experimental animals with toxicology, as well as in humans.
"But here's what I know about brain cancer: It can take 40 years before it develops after exposure starts. And we know that because, after the bombs fell on Hiroshima, there was no increase in brain cancer 10 years later in the survivors. There was no increase 20 years later. The increase only showed up in a statistically significant way after 40 years of exposure.
"And for tobacco and asbestos, we have a similar story -- 10 years after people started to smoke or use asbestos there was no increase in risk of any significance. However, 20, 30 and 40 years later, there's a big risk.
"Here's where it gets really hard and it's really important, and frankly why I wrote the book: We are already seeing a doubled risk of brain cancer in people who have used cell phones heavily for 10 years in the few studies that have been done. And most of us have not used phones heavily for 10 years."
Major public health officials say published studies support the safety of cell phones, but you argue the opposite. What are the most compelling studies you've seen that support the connection between cell phone radiation and health problems?