The World Health Organisation (WHO) has reclassified the radio frequency electromagnetic fields generated by mobile phones as possibly carcinogenic to humans.
The International Agency for Research on Cancer (IARC), the division of WHO which investigates cancer, said that it is reclassifying the radiation as Group 2B (PDF), its rating for agents that possibly cause cancer, as opposed to probably causing it (Group 2A) and definitely carcinogenic (Group 1).
"The evidence, while still accumulating, is strong enough to support a conclusion and the 2B classification," said Dr Jonathan Samet, chairman of the IARC Working Group.
"The conclusion means that there could be some risk, and therefore we need to keep a close watch for a link between cell phones and cancer risk."
An IARC team of 31 cancer experts from 14 countries has reviewed the evidence of the health risks of mobile phones, and found two specific types of brain cancer that showed an evidential increased risk: glioma and acoustic neuroma.
The evidence was inadequate to draw a conclusion on other forms of cancer, the team found.
One study cited by the team found that the heaviest mobile phone users, i.e. those connected for more than 30 minutes a day for 10 years or more, showed a 40 per cent increase in glioma cases. The full report will be published in The Lancet Oncology on 1 July.
"Given the potential consequences for public health of this classification and findings it is important that additional research be conducted into the long-term, heavy use of mobile phones," said IARC director Christopher Wild.
Imperial College London is currently conducting one of the world's biggest studies into the issue, with over 250,000 participants.
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