The warning is based on evidence that intensive use of mobile phones and other wireless devices might lead to an increased risk of glioma, a malignant form of brain cancer.
WHO’s the International Agency for Research on Cancer concluded that the radio frequency electromagnetic fields generated by such devices was “possibly carcinogenic to humans”.
WHO had previously said that there were no ill-effects from mobile phone use.
A team of 31 scientists from 14 countries made the warning after assessing hundreds of published studies into the potential cancer risks posed by electromagnetic fields.
The scientists said there was not enough evidence to conclude that radiation from mobile phones was safe, but there was enough data to show a possible connection to tumours.
Evidence of harm
Jonathan Samet, who chaired a meeting of the scientists in the French city of Lyon, said: “The conclusion means that there could be some risk, and therefore we need to keep a close watch for a link between cellphones and cancer.”
The WHO has put mobile phone radiation on a par with about 240 other agents for which evidence of harm is uncertain, including talcum powder, working in a dry cleaner’s, pesticide DDT, petrol engine exhaust and coffee.
Two studies in particular, the largest conducted over the last decade, provided evidence that mobile phone use was associated with higher rates of glioma, “particularly in those that had the most intensive use of such phones”, Dr Samet said.
A number of individuals tracked in the studies had used their phones for 10 to 15 years.
“We simply don’t know what might happen as people use their phones over longer time periods, possible over a lifetime,” he said.
There are about five billion mobile phones registered in the world. Both the number of phones in circulation, and the average time spent using them, have climbed steadily in recent years, the working group found.
The IARC cautioned that their review of scientific evidence showed only a possible link, not a proven one, between wireless devices and cancers.
“There is some evidence of increased risk of glioma” and another form of brain cancer called acoustic neuroma, said Kurt Straif, the scientist in charge of editing the IARC reports on potentially carcinogenic agents.
“But it is not at the moment clearly established that the use of mobile phones does in fact cause cancer in humans,” he said in a telephone press conference.
The IARC does not issue formal recommendations, but pointed to a number of ways consumers can reduce risk.
“What probably entails some of the highest exposure is using your mobile for voice calls,” Dr Straif said.
“If you use it for texting, or as a hands-free set for voice calls, this is clearly lowering the exposure by at least an order of magnitude,” or by ten fold, he said.
A year ago the IARC concluded in a major report that there was no link between mobile phones and brain cancer, but the review was widely criticised as based on out-of-date data that did not correspond to current usage levels.
The new review, conducted by a panel of 31 scientists from 14 countries, was based on a “full consensus,” said Robert Baan, in charge of the written report, yet to be released.
Exposure data, studies of cancer in humans, experiments on animals and other data were all evaluated in establishing the new classification.
The IARC ranks potentially cancer-causing elements as either carcinogenic, probably carcinogenic, possibly carcinogenic or “probably not carcinogenic.” It can also determine that a material is “not classifiable”.
Cigarettes and sunbeds, for examples, are rated as “group 1”, the top threat category.
AMA says no need to panic
Australian Medical Association Queensland president Dr Gino Dr Pecoraro said people shouldn’t panic and it’s really “early days”.
“I think it’s very interesting. I’ve only read an excerpt… it’s not worth creating hysteria or panic about it, we don’t want people becoming unnecessarily afraid,” Dr Pecoraro said.
“If they’ve said there’s some evidence then people need to be aware of this but we need to point out that the link is too weak to claim any clear recommendation at this stage.
“We need to be aware of it and if the WHO said there is some evidence we need to listen to them, there’s not enough clear evidence to take action.”
Dr Pecoraro said people should think about using their mobile phone and use hands free or text where possible.
“My understanding is the concern is around radiation and heating associated with the transmission of the signal,” he said.