Researchers have for the first time established a link between mobile phone radiation and damage to the human brain.
Finnish scientists found emissions from handsets led to deterioration in the blood-brain barrier, the layer that protects the brain from potentially harmful substances.
Cells from blood vessel walls in the brain were placed in culture dishes and subjected to mobile phone radiation in the laboratory.Exposure caused the cells in blood vessel walls to shrink, enabling molecules to pass into brain tissue.
Prof Darius Leszcynski, of Finland's Radiation and Nuclear Safety Authority, which carried out the study, warned such changes could pose a serious health risk.
He said : "If the same thing happened in real life, in people, then it could affect blood-brain barrier permeability by increasing it."
A French team has also shown that blood-brain barrier leakage was increased in rats exposed to mobile phone radiation.
The Irish mobile phone industry said the findings actually supported its insistence that handsets are safe.
A spokeswoman for the Irish Cellular Industry Association, an umbrella group representing the three mobile networks, Vodafone, O2 and Meteor, said the deterioration recorded by researchers was no more significant than the alteration to the body's chemical balance caused by drinking a glass of water.
Carphone Warehouse's chief executive in Ireland, Mr Stephen Mackrel, cautioned against reading too much into the study.
He said: "At the moment there is so much contradictory evidence it is difficult to know what to make of it all."
Over 77 per cent of the Irish population - approximately 3 million people - own mobile phones.