Using a mobile phone can slash a man's sperm count by almost a third, new research suggests.
A study found that radiation from mobile phones appeared to have a dramatic impact not only on numbers of sperm, but also their swimming ability or "motility".
In both cases, levels were cut by about 30 per cent. Reductions in sperm count and motility lower the chances of conception.
The research is the first to show that male fertility may be damaged by electromagnetic signals from mobile phones.
A team led by Dr Imre Fejes, from the University of Szeged in Hungary, looked at 221 men for a period of 13 months.
Sperm from very active users of mobiles was compared with that of non-users.
Dr Fejes found that men who carried a phone with them on stand-by throughout the day had significantly lowered sperm concentration.
Their counts averaged at 59.11 million sperm per millilitre of seminal fluid compared with 82.97 million for men not continually exposed to mobile phone radiation.
Motility was similarly affected by mobile phone transmissions, the study found.
Men who made lengthy calls had fewer rapidly motile sperm - 36.31 per cent compared with 51.34 per cent for men who made no calls.