Men who use laptops could be risking their fertility, a US study warns. Heat from the processor can cause the temperature of the testes to rise almost three degrees, more than enough to damage sperm, the research reveals.

Researchers at the State University of New York at Stony Brook have warned men to be careful about using notebook computers on their laps.

Yefim Sheynkin, director of male infertility and microsurgery at the university, said: "As well as being capable of producing direct local heat, they require the user to sit with his thighs close together to balance the machine, which traps the scrotum between the thighs."

Sheynkin explained that sperm concentration could be decreased by 40 per cent per 1°C increase. "The body needs to maintain a proper testicular temperature for normal sperm production," he said.

The researchers found that after just fifteen minutes use, the temperature of the scrotum had risen by 1°C. After more prolonged use, the temperature rose by as much as 2.8°C. Earlier studies have shown that temperature rises in this range have a detrimental effect on sperm production.

The study, which was published in the journal Human Reproduction, recommends that men keep their laptops on their desks, to avoid making "irreversible changes" to their fertility. ®

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