Exposure to hot baths or hot tubs can lead to male infertility, but the effects can sometimes be reversible, according to a new study led by a University of California, San Francisco urologist.

Results from a three-year study analyzing data from infertile men who had been repeatedly exposed to high water temperatures through hot tubs, Jacuzzis or hot baths are reported in the March-April 2007 issue of "International Braz J Urol," the official journal of the Brazilian Society of Urology. Study findings will be available online at www.brazjurol.com.br.

"It has been believed for decades that wet heat exposure is bad for fertility, as an old wives tale, but this effect has rarely been documented," said Paul J. Turek, MD, lead investigator who is a professor in the UCSF Department of Urology and director of the UCSF Male Reproductive Health Center. "We now have actual evidence to show patients that these recreational activities are a real risk factor for male infertility."

Although this was only a pilot study, Turek said, "these activities can be comfortably added to that list of lifestyle recommendations and things to avoid as men attempt to conceive."

Dry heat exposure, for instance, as presented with fevers or through applied external heat, is a well-documented cause of impaired sperm production in both animals and humans, according to Turek. This is the first published study to show that total body exposure to wet heat can also impair both sperm production and motility. Study findings also showed that the negative effect of this exposure was reversible in nearly half of the infertile men who discontinued the practice.

An estimated 7 percent of American couples report that they are unable to conceive a child naturally within one year, according to the 2002 National Survey of Family Growth, the latest data available to the Centers for Disease Control and Prevention.