An international panel of experts is classifying the radiation from cellphones as "possibly carcinogenic" to humans.

After reviewing dozens of published studies on the matter, the International Agency for Research on Cancer placed cellphone radiation in the category of 2B: "possibly carcinogenic."

Other substances the cancer agency of the World Health Organization has placed in the 2B category include the pesticide DDT, chloroform and gasoline engine exhaust.

What the designation means is that the evidence so far doesn't offer a clear conclusion on whether radiation from cellphones is safe, but there is enough data showing a possible increased risk for a type of brain cancer called glioma that cellphone users needed to be alerted.

A total of 31 scientists reviewed all the literature to date on the electromagnetic radiation found in cellphones, and decided there was "limited" evidence of a link between cellphone use and glioma and acoustic neuroma, a cancer that develops in the nerves leading from the ear to the brain.

There was "inadequate" evidence to draw conclusions about other types of cancers.

Last year, results of a large, 10-year study, called Interphone, found no clear link between cellphones and cancer. But that study also found that very frequent phone users had a 40 per cent higher risk of glioma compared to people who never used cellphones. They also had about twice the risk of developing tumours on the same side of their heads where they normally held their phones while talking.

The IARC group said they looked at the evidence from that study along with many others and decided it was "credible" that exposure to cellphone radiation could be a cause of brain cancer, "but chance, bias or confounding could not be ruled out with reasonable confidence."

Researchers also noted that some of the epidemiological studies they examined were based on phones that used older technology, and that the radiation emitted from cellphones has dropped over time.

As for what cellphone users can do to reduce the possible risks from cellphone radiation, the researchers noted that some studies have found reduced risks among phone users who talked less and texted more, and those who used a hands-free device to keep the phone away from their heads.

"Given the potential consequences for public health of this classification and findings," said IARC Director Christopher Wild, "it is important that additional research be conducted into the long-term, heavy use of mobile phones. Pending the availability of such information, it is important to take pragmatic measures to reduce exposure such as hands-free devices or texting."

It's estimated that about 5 billion cellphones are currently in use worldwide.

Bernard Lord of the Canadian Wireless Technologies Association notes that the study says "possibly" -- not "probably" -- carcinogenic.

"It says there is a possible link -- that they need more information and more study. We support the fact that . . . more studies are needed. Let's go out and conduct more studies," he said.

Lord also said modern cellphones are smaller, use less power and are more often used for texting and emailing.