Men seeking to become a father should avoid soaking in hot baths, according to a study on male fertility.

A three-year pilot project involving 11 men found that there was some truth in the old wives’ tale about hot baths being bad for a man’s prospects of conceiving. The men were exposed to “wet heat” in the form of a hot tub, Jacuzzi or bath, at least once a week for 30 minutes or more for three months.

Scientists studied sperm quantity and quality after the bathing stopped and found that five of the 11 men experienced a significant increase in fertility. After three to six months of staying out of the bath, the men’s average active sperm count increased almost fivefold. Motility, a measure of sperm’s ability to swim, rose by a third by the end of the study. Researchers suspect smoking may have been a factor in the six men who did not experience an increase in sperm count or motility.

“It has been believed for decades that wet heat exposure is bad for fertility, but this has rarely been documented,” said Dr Paul Turek, from the University of California at San Francisco, who led the study published in the journal of the Brazilian Society of Urology.“These activities can be comfortably added to that list of lifestyle recommendations as men attempt to conceive,” he said.

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Brazilian Society of Urology