data briefing

A major study is investigating whether health risks from mobile phones are genuine or the latest in a long line of unfounded fears, writes John Appleby

From BSE to low-level radiation, from the contraceptive pill to genetically modified foods, it seems scientists are increasingly being asked by a worried public to do the impossible: to prove the non-existence of harmful risks.

The problem for science is that no such negative certainty exists. Scientists can never say never, and all scientific facts and theories are only true until an example arises to disprove them. But even when an observation is made which fails to fit the facts, this does not necessarily invalidate the inferences drawn from the facts, it just makes them a bit less true.

But qualifying phrases often used by scientists to describe the results of their research frequently do little to assuage the public's fears.

Paradoxically, often the smaller the degree of uncertainty expressed by scientists, the worse the effect can be on the public's perception of risk.

This is particularly true when exposure to a risk is seen to be involuntary - for example, exposure to environmental hazards such as mobile-phone base stations.

Worries about the health risks associated with electromagnetic fields from gamma and x-rays via visible light through to microwaves, radiowaves and the frequency emitted by mains electricity have a long history. Fears in the 1960s that colour televisions produced harmful x-rays proved erroneous; worries in the 1970s and 1980s that computer screens were responsible for birth defects also proved unfounded. Overhead power cables in the 1990s were also a source of concern. Again, however, little firm evidence appeared to support the fear of health risk.

And now we have mobile phones. According to urban myth, if a raw egg is left by a switched-on mobile phone it will be cooked within a couple of hours.

While ionising radiation such as x-rays have the power to break chemical bonds and damage DNA, the non-ionising frequencies used by mobile phones are much less powerful (and only one-thousandth that of microwave ovens). There seems to be a very slim chance indeed of cooking your brain.

In fact, a bit of mild exercise will raise the temperature of your brain more than a mobile phone. Not only that, there are no studies which indicate that users of mobile phones suffer more cancers than non-users. And, although there have been suggestions that mobiles have been linked to memory loss, at least one study suggests this is very unlikely indeed, finding a slight improvement in the response times to various word-related computer tests of subjects exposed to radiation equivalent to that from mobile phones.

Nevertheless, the World Health Organisation, as part of a large study into the health effects of electromagnetic fields, is to embark on a large study of the effects of mobile phones on health.

The study will cost around£3.75m and will involve around 3,000 European mobile-phone users together with a control group.

The results of the study will not be known for some years, by which time the number of mobile phone users will have nearly doubled to around 700 million worldwide. The nature of this scientific investigation will mean that an answer of 'no harm whatsoever' will not be one of the conclusions. As long as the perceived benefits outweigh the perceived (and researched) risks, and the mobile phone becomes just another commonplace electronic appliance, users will carry on using them.