But the sheer volume of use, as well as a few studies that found a potential link between brain cancer and cellphones, have kept the safety question looming.

The US National Academy of Sciences released a report in January calling for more research on cellphones and health risks. The authors concluded that many of the past studies were not conducted over a long-enough period of time to assess the risk of brain cancer, which typically develops slowly.

Nor have the studies examined the effects of cellphone use on children, whose nervous systems are still developing, or on whether the radio frequency emissions can cause other types of health problems, such as cancers elsewhere in the body or central nervous system damage that may affect learning or behaviour, says Dr Leeka Kheifets, a professor of epidemiology at the University of California, Los Angeles’ School of Public Health and a member of the NAS panel.

“At this point, it looks unlikely that cellphones are causing brain tumors, particularly from short-term exposures,” says Kheifets. “But we have not looked at all outcomes yet. The focus has been on brain tumors because exposure from cellphone use is mostly to the brain. And we are just beginning some studies on brain cancer in children.”

Kheifets and researchers in Denmark recently examined cellphone use in children and found “unexpected results”.

The researchers examined 13,159 Danish children born in 1997 and 1998 who are participants of a study called the Danish National Birth Cohort. The children’s mothers were surveyed during pregnancy and again when the children were 18 months old and 7 years old.

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