Cell Phones in Pockets a Health Risk?

More than four billion people worldwide use cell phones every day. There's still some concern about a possible link to brain cancer from holding the devices up to your ear.

Now, another worry: Should you keep your cell phone in your pocket?

"Cell phones," CBS News Medical Correspondent Dr. Jennifer Ashton told "Early Show" co-anchor Harry Smith, "emit a type of energy known as radiofrequency energy. It's low level. But the concern here is that, at high levels, it can actually cause what's called a thermal injury, or heating up tissue.

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"At high levels, this is a microwave. At low levels, it's a cell phone.

"If you read the fine print on your particular phone (in its users' manual, say, Apple: They say, for wireless data transmission over a cellular network, keep the iPhone at least 15 millimeters (5/8ths of an inch) away from the body. If you look at what BlackBerry says, they'll say keep the BlackBerry device at least 0.98ths of an inch from your body when the device is transmitting. If you put it in a holster, probably it will be over these minimum distance requirements. But if you slip it in your pocket, either your shirt pocket or pants pocket, it's gonna be directly next to your skin."

Research on the radio waves themselves is, Ashton says, "ongoing and it's controversial. You'll find as many studies that say there could be a risk as there will be those that say no risk.

"(A study coordinated by the World Health Organization and released in May), called Interphone, the largest study to date, done over a period of ten years in many countries (though not the U.S.) said there could, we have to emphasize could, be an increased risk of certain types of brain tumors with very heavy cell phone users. (BUT more research was needed, because brain tumors could take decades to develop)

Other than hands-free devices, Ashton noted, another way to keep cell phones further from your head is "the obvious one," namely, to "try not to use it that much. But, as we know, most of us really can't get through a day without heavy cell phone use. But putting it on speaker mode is one way.

"You have to be careful with wireless or hands-free devices because, if you attach something to your ear, you're potentially still getting that radio frequency energy. You don't want to sleep with your cell phone directly next to your bed, like most of us do, or under your pillow and, most importantly, because children's skulls are thinner, you need to really monitor this use in kids."

"Holsters" for cell phones can also be helpful, Ashton says.

And she stressed that different cell phones emit different amounts of energy.

For a complete guide to radiation given off by cell phones, click here.