Here are answers to questions about Herberman's memo, the science on cell phone safety, and whether you should set limits for your kids -- and yourself -- to minimize risk.

What was in the cell phone memo?

A University of Pittsburgh Medical Center spokeswoman tells WebMD that Herberman was not available to comment on the memo and that the memo wasn't available for her to forward.

According to the Associated Press, Herberman's memo recommends that children use cell phones only in emergencies because their brains are still developing, and that adults should keep cell phones away from their head, using the speakerphone or a wireless headset. Similar advice is also posted in an article on the web site of the University of Pittsburgh Cancer Institute's Center for Environmental Oncology.

What was the memo based on?

Herberman's memo reportedly acknowledges that his concern is based on early, unpublished data -- not published studies -- and on caution that science moves slowly and that it's better to be "safe rather than sorry later," the Associated Press quotes Herberman as saying.

What does the FDA say?

The FDA hasn't posted a specific reply to Herberman's memo, but the FDA's web site has lots of information on cell phones and health.

"The available evidence does not show that any health problems are associated with using wireless phones. There is no proof, however, that wireless phones are absolutely safe," states background information on the FDA's web site.

The FDA explains that wireless phones emit low levels of radiofrequency (RF) while being used and very low levels of RF in standby mode.

"Whereas high levels of RF can produce health effects (by heating tissues), exposure to low-level RF that does not produce heating effects causes no known adverse health effects," the FDA states. "Many studies of low-level RF exposures have not found any biological effects. Some studies have suggested that some biological effects may occur, but such findings have not been confirmed by additional research. In some cases, other researchers have had difficulty in reproducing these studies, or in determining the reasons for inconsistent results."

What does the American Cancer Society say?

Michael Thun, MD, is the American Cancer Society's vice president for epidemiology and surveillance research.

"The first thing we say is that if someone is concerned about the risk of cell phones, you can virtually eliminate your exposure by using a headset or a speaker phone or having the phone farther from your ear," Thun tells WebMD.

What does the American Cancer Society say? continued...

"With respect to the science ... we, and the epidemiologists who I respect who are involved in this, find the evidence to be much, much weaker than it's being presented by some proponents," says Thun, noting that cell phone emissions are "not ionizing radiation that damages DNA" and that of the 17 studies on cell phone use and brain cancer, only two have suggested an association, and those studies' methodologies are "weaker than some of the larger, better studies."

Thun points out that in Sweden, one of the countries where cell phones caught on early, up to 25 years of data show no signs of increased brain cancer rates. He also says that the American Cancer Society is "seriously considering" convening an independent group of scientists to look at the epidemiologic data.

But Thun notes that cell phones are widely used and that "the evidence is quite extensive, but incomplete in important ways." For instance, he says more studies are needed on the long-term effects of children's cell phone use.

"On the one hand, it's important to be prudent and have an appropriate level of caution, and on the other hand, it's important not to sound false alarms, because they, too, have unintended consequences. If you sound too many of them, nobody believes anything you say, and if there is not a problem, they distract attention away from real problems, of which we have a lot."

Should parents limit kids' cell phone use?

Fisher, who spoke to WebMD via cell phone, says he sees good reason to limit kids' cell phone use -- just not out of cancer fears.

"I restrict my own kids' use of cell phones. We don't sit in bed and talk on our cell phones at night, and we don't get to use them when we're 5 years old. But that's more about good parenting and parental choice than about science," Fisher says.

"Common sense should prevail," he says, noting that kids can get distracted by cell phones. "I don't think kids should be given unrestrained access 24-7 to cell phones. It should be limited. But it shouldn't be done because of paranoia or fear of perceived risks that aren't established."

Setting limits "out of your own philosophy and life choices, that's very different than doing it out paranoia. That's why I'm disappointed by the statement from the folks in Pittsburgh ... it's not an appeal to healthy living and happy development for children, it's an appeal to people's paranoia about modern living."

What does the wireless industry say?

Here's what Joe Farren, assistant vice president for CTIA -- the Wireless Association (the industry group for wireless communication, including cell phones), says.

"We have always believed this issue must be guided by science. And when you examine the overwhelming majority of studies that have been peer-reviewed and published in scientific journals, you'll find no link between wireless usage and adverse health effects," Farren tells WebMD.

"This isn't just our opinion. This is the view of leading global health organizations such as the American Cancer Society, the World Health Organization, and the U.S. Food and Drug Administration."

Farren notes that Herberman's views "are not based on scientific evidence."

What does the research say?

No studies have proven that cell phones cause brain cancer or other health problems. But none has ruled out health risks once and for all, either.

Here's a quick recap of recent studies on cell phone use and cancer. These studies don't directly test cell phones to see if they cause cancer; rather, they're observational studies in large groups of people. Observational studies don't prove cause and effect.

In February 2008, Israeli researchers reported no overall increase in the risk of tumors in the parotid gland (a salivary gland) with regular cell phone use, with a possible (but not confirmed) increase in risk in people who use cell phones a lot more than normal. That contradicts a Swedish study published in 2006 that showed no increased risk of parotid gland tumors for any amount of cell phone use.

In 2007, French and Norwegian studies published in European journals showed no increased risk of brain tumors in adults from regular cell phone use.