The bulk of research into cellphones and their base towers has found no definitive evidence that short-term use poses significant health risks to humans. So, policy makers have given industry the green light, allowing the use of wireless gear to explode around the world, to about five billion wireless subscriptions worldwide, by the World Health Organization's estimate.

Now that the technology has been widely used for a number of years, researchers have turned their attention to exploring possible effects of long-term exposure to the electromagnetic fields (EMF) the radiofrequency waves used to transmit cellphone communications create.

In May 2011, the WHO's International Agency for Research on Cancer did a review of existing research on the effects of exposure to such electromagnetic fields. It found that, for most cancers, the available evidence was inadequate to make any conclusions about risk.

In the case of glioma, a type of brain cancer, and acoustic neuroma, a slow-growing non-cancerous tumour in the inner ear that results in hearing loss, the existing evidence was limited. This means the group found that evidence of a causal relationship between cellphone radiation exposure and increased risk of developing one of those diseases was credible but could not rule out that chance or bias had played a role in establishing that relationship.

Nevertheless, the group found that in the case of glioma, the evidence was significant enough to warrant classifying radio frequency electromagnetic fields as "possibly carcinogenic to humans," a WHO category known as 2B, and to warrant further study of a possible link between wireless use and cancer risk, the group said.

Earlier reviews of research done by the European Commission and by Swedish scientists, whose results were published in the journal Occupational and Environmental Medicine, found some evidence of increased relative risk of glioma and acoustic neuromas after more than 10 years of cellphone use. But these studies also said the majority of papers on the topic reported no connection between 10 years of mobile phone use and disease.

Another study — published July 27, 2011, in the Journal of the National Cancer Institute — looked at children from Norway, Denmark, Sweden and Switzerland, aged 7 to 19. It found that those with brain tumours were not statistically more likely to have been regular cellphone users than the control subjects.

Supporting data on either side of the debate is limited. Health Canada, the Food and Drug Administration in the U.S. and the European Union have based their cellphone regulations on the majority of evidence available so far.

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