Men who keep their mobile phones in trouser pockets or on bedside tables at night may be damaging their chances of becoming a father.
Sperm levels and quality fell in men who kept their phones in their pockets during the day or within a foot or two of the body, a study found.
Martha Dirnfeld, from Technion University in Haifa, said: “We analysed the amount of active swimming sperm and the quality and found that it had been reduced.
“We think this is being caused by a heating of the sperm from the phone and by electromagnetic activity.”
Nearly half of the men – 47 per cent – who carried their phones in their pockets had an abnormal level of sperm concentration, compared with only 11 per cent in the total male population.
The study was carried out at a fertility clinic in Israel and 106 men took part.
Researchers also found that frequently talking on a mobile phone for more than an hour a day or while it was being charged doubled the likelihood of lower sperm concentration.
Gedis Grudzinskas, a fertility consultant at Harley Street and St George’s Hospital, told The Times: “Men need to think about their wellbeing and try to stop being addicted to their phones.
“If you wear a suit to work put the mobile in your chest pocket instead of close to your testes. It will reduce the risk of your sperm count dropping or dropping so much.”