In its attempt to provide the most authoritative verdict yet on the risks associated with mobiles, the WHO reviewed 21 credible scientific studies from 14 countries worldwide.
So just how dangerous is your mobile? Here, we offer a dispassionate analysis . . .
How risky are they?
The WHO concluded mobile use is 'possibly carcinogenic to humans', a term that places mobiles in the middle of a rating scale that contains five levels of carcinogens.
This means mobiles are ranked below things that are definitely known to cause cancer — such as smoking and sun beds.
They are instead put alongside thing over which there are still questions, such as pesticide DDT and lead.
The WHO says that, while we still need more studies, we should err on the side of caution. It pointed to a study from last year that linked just 30 minutes of mobile use a day for ten years with an increased likelihood of glioma, a type of brain tumour.
What do they emit?
Mobiles emit signals in the form of radio waves. These microwaves are a form of electromagnetic radiation.
When we hold a mobile against our ear, the radiation is in direct contact with the tissue in our head.
The fear is that this radiation can cause changes to the cells in our brains.
If the DNA in these brain cells gets damaged they may become cancerous and cause brain tumours, in particular gliomas.
These are a rare type of tumour that typically starts in the brain or spine and can cause headaches, nausea, vomiting and seizures. They are usually incurable.
It's also feared that the radio waves can alter chemical and electrical reactions in our brains, changing, in effect, the way that the brain's cells communicate. This may cause emotional disorders.
Why worry?
Glioma might be rare normally, but if it does affect mobile users it could become a widespread problem due to the rise in phone use.
There are now more mobiles in use in Britain than there are people. And we are using them more than ever.
This is particularly true among the young. It's thought 97 per cent of 11 to 16-year-olds now own a mobile phone, according to the research firm ChildWise.
This means that safer landline phones are dying out. Around 15 per cent of homes now don't have a landline.
Is cancer the only concern?
Detailed academic studies conducted in 2004 in Sweden by Professor Leif Salford, of Lund University, concluded cancer was not the only risk.
He found radiation could kill off brain cells, leading to senility.
Professor Salford spent more than 15 years studying the effect of mobile phones on the brain. In experiments, he exposed 1,600 rats to the levels of radiation emitted from mobiles and concluded their brain cells were damaged.
The more radiation the rats received, he said, the worse the effect.
And since children are the most vulnerable to mobile use, he said: 'We cannot exclude the possibility that, after some decades of daily use, a whole generation may suffer negative effects, perhaps as early as in middle age.'
What's happening to your brain?
A U.S. study this year found using a mobile phone can change the activity of brain cells.
The report, in the Journal Of The American Medical Association, found that just 50 minutes of mobile radiation significantly raised the brain's level of glucose.
This change happened in the parts of the brain that received the most cell phone radiation.

The researchers, from the California Institute of Technology, say that increased glucose in the brain is associated with inflammation and may indicate that cells are being damaged in ways that could raise the risk of brain tumours.
There is other evidence of physical changes in the brain caused by mobiles.
In a study in the journal Nature Neuroscience earlier this year, neurobiologists at the California Institute of Technology showed that very weak electric fields, such as those emitted by mobiles, can affect the electrical activity in the thinking, resting, and sleeping brain.
It is not known, however, what effects these fields may ultimately have.
Are children more vulnerable?
It's not just that a child's bone structure in the skull is less dense, and therefore less protective against electromagnetic radiation.
Some scientists believe that radiation from mobiles may interfere with children's brains because they are still forming. This may render them more vulnerable.
In 2000, the former government chief scientific adviser Sir William Stewart said children were exceptionally at risk from mobiles and that those under the age of eight should use them only in emergencies.
Two years ago, a Swedish study warned children who use mobiles are five times more likely to develop glioma brain tumours.
The Department of Health currently recommends that those under the age of 16 should be 'discouraged' from using mobile phones for 'non-essential calls'. It adds that these guidelines are currently only precautionary.
But some studies have turned up alarming results. In 2008, research done in Moscow claimed children who use mobiles are more likely to face a range of problems which include memory disruption, decline in attention spans, diminished learning ability, increased irritability, sleep problems and increased stress.
Has anyone sued?
No, but this is not for want of trying. In the U.S., there have been three high-profile cases, all of which were won by the mobile companies.
In 2000, a judge threw out a £500 million lawsuit against mobile phone manufacturer Motorola brought by a neurologist who claimed that using his phone gave him brain cancer.
Dr Christopher Newman said the mobile phone he used from 1992 to 1998 gave him a cancerous tumour behind his right ear. The tumour was removed, but he became permanently blind and disabled.
But Baltimore judge Catherine Blake ruled that none of the evidence submitted by Dr Newman was substantial enough to warrant a trial.
How can you protect yourself?
The two best, common-sense, preventative methods are highly effective at cutting your brain's exposure to microwave radiation, according to the WHO report.
You should use a hands-free system so that the phone isn't near your head, and send texts whenever possible rather than phoning someone.
It's also wise to use an up-to-date phone, according to Professor Bruce Armstrong, of the University of Sydney, who was one of the experts involved in the WHO report.
He says that the 3G technology used by iPhones, Blackberries and other new models appears to emit less harmful radio waves than 2G devices.
He says: 'The 3G phones give a much lower dose to the brain than the previous generations.
'Whether the 3G levels are sufficient to cause brain tumours, we don't know at this stage, because most of the research at this stage was done on the generation before.'
Source:
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