MOBILE phone radiation may cause serious damage to the brain by triggering a chemical reaction that leads cells to divide, say scientists.
The finding could be the key to claims that mobiles cause cancer and other health problems.
Fear over their use has centred on "brain heating", but Dr Joseph Friedman and colleagues say the real risk is low-intensity radiation - known as non-thermal radiation.
The Israeli researchers have identified a mechanism through which the radiation may affect the differentiation and division of cells.
There have been suggestions mobile phones can cause brain tumours and Alzheimer's disease, but research has been inconclusive and manufacturers take great care to ensure their gadgets do not overheat users' brains.
No clear mechanism is yet known by which radiation at mobile frequencies and power levels could harm living cells.
The frequencies are too low to damage DNA directly and the power of the signal is well below the level that could overheat cells.
Researchers at the Weizmann Institute of Science in Rehovot exposed rat and human cell cultures - and isolated cell membranes - to low-level electromagnetic radiation at 875 megahertz - a similar frequency to those of GSM phone signals.
After only ten minutes of exposure the team identified activation of the pathway for an enzyme that regulates cell differentiation and division.
The researchers, whose findings are published in Biochemical Journal and reported by New Scientist, concluded the chemical trigger for the enzyme is the release of reactive oxygen species, small molecules which damage DNA, in cell membranes.