The World Health Organization (WHO) has determined that radiation from phones could possibly increase brain cancer risk, a change in thinking for an organisation that has previously found no evidence of any such link.

The decision is based on the judgment of a group of 31 scientists from 14 countries who reviewed a collection of the latest research earlier this month. The decision is sobering considering there are some 5 billion cell phones in use now.

"The WHO/International Agency for Research on Cancer (IARC) has classified radiofrequency electromagnetic fields as possibly carcinogenic to humans... based on an increased risk for glioma, a malignant type of brain cancer, associated with wireless phone use," the WHO reports

WHO recommends that users limit their exposure to such radiation if possible, though also said more research is needed to verify an absolute link between mobile phone use and cancer (the scientists also studied occupation exposure to radar and microwaves as well as environmental exposure to radio, TV and wireless communications signals).

Results released last year from a 10 year, £14 million study by WHO on a possible link between cell phone use and cancer were inconclusive.

The Cellular Telecommunications Industry Association (CTIA) was quick to point out the limits of the latest WHO/IARC conclusion:

"Today, an International Agency for Research on Cancer (IARC) working group in Lyon, France categorised radiofrequency fields from cellphones as 'possibly' carcinogenic based on 'limited evidence.' IARC conducts numerous reviews and in the past has given the same score to, for example, pickled vegetables and coffee. This IARC classification does not mean cellphones cause cancer. Under IARC rules, limited evidence from statistical studies can be found even though bias and other data flaws may be the basis for the results."

"The IARC working group did not conduct any new research, but rather reviewed published studies. Based on previous assessments of the scientific evidence, the Federal Communications Commission has concluded that '[t]here's no scientific evidence that proves that wireless phone usage can lead to cancer.' The Food and Drug Administration has also stated that '[t]he weight of scientific evidence has not linked cellphones with any health problems.'"

CNN, in its report on the study quotes a doctor who says coming up with a real answer can take a long time: "The biggest problem we have is that we know most environmental factors take several decades of exposure before we really see the consequences," said Dr. Keith Black, chairman of neurology at Cedars-Sinai Medical Center in Los Angeles.

Daring Fireball blogger John Gruber wrote in light of the WHO announcement: "I think it's quite possible that this issue could be the single greatest long term threat to Apple. I'd hate to see today's handset makers turn into yesterday's tobacco companies." Though he updated his post to stress that WHO said a link can't be ruled out, not that it's definite.