A warning against the use of mobile telephones has been issued by the World Health Organisation after scientists identified a potential link with a type of brain cancer.
Researchers analysing the evidence for a link between mobile phone use and brain cancers concluded there "could be some risk" of the brain cancer glioma being caused.
In response to the finding, the WHO's International Agency for Research on Cancer (IARC) urged the public to use hands-free devices rather than have phones pressed against their heads, and to send text messages where possible instead of calling.
The research team found that the overall evidence was "limited" but felt there was enough evidence of a link to glioma to justify classifying mobile phone use as "possibly carcinogenic to humans". For all other types of cancers the evidence against mobile phone use as a cause of cancer was regarded as being "inadequate" so they were unable to draw any conclusion for them.
On gliomas, however, they were concerned that the evidence was mounting. The IARC cited a 2010 study which identified a 40 per cent increase in the level of risk for people who in the 10 years up to 2004 had used mobile phones for an average of 30 minutes or more every day.
Dr Jonathan Samet, of the University of Southern California, led the group that analysed the evidence. He accepted that it was "still accumulating" but said: "There could be some risk, and therefore we need to keep a close watch for a link between cellphones and cancer risk."
His colleague Christopher Wild, the director of IARC, added: "Given the potential consequences for public health of the findings it is important 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."
The finding reignites the debate over how safe mobile phones are and whether usage has serious health consequences for the five billion worldwide who use them. There have been dozens of studies, but a categorical cause-and-effect link has yet to be established. However, a lack of evidence could simply mean that mobile phones have not been in widespread use for long enough for their full effect to be felt – many brain tumours take years to develop.
The Health Protection Agency (HPA) noted the conclusion, but said it already advocates a precautionary approach in case of "long-term effects which are presently unknown".
It added: "Given the possibility of long-term cancer effects, excessive use of mobile phones by children should be discouraged." However, it pointed out that magnetic fields from electricity, coffee, petrol exhaust fumes and being a print worker come under the same "possibly carcinogenic" classification as mobiles.
Ed Yong, of Cancer Research UK, said: "The WHO's verdict means that there is some evidence linking mobile phones to cancer, but it is too weak to draw strong conclusions from. The vast majority of existing studies have not found a link between phones and cancer, and if such a link exists, it is unlikely to be a large one.
"The risk of brain cancer is similar in people who use mobile phones compared to those who don't, and rates of this cancer have not gone up in recent years despite a dramatic rise in phone use. However, not enough is known to totally rule out a risk."
20 years of research
1991 National Radiological Protection Board suggests mobiles could affect brain.
2000 The Stewart report finds no problem but recommends caution.
2006 A Danish study of 420,000 people over 20 years finds no increased risk.
2010 Biggest study so far mainly inconclusive.