When Mark Jordan was a 22-year-old substitute teacher in Phoenix, he had been smoking for about a year and noticed the fire in his love life was no longer raging.

"Sex was suddenly getting boring," he says. "I didn't want to have it. I would get out of breath so easily, and I simply felt gross." While he averaged only half a pack a day, he often smoked much more on the weekends. The effects were not good.

"I remember having sex in the shower and feeling like I was going to pass out," he says. That was a turning point. He stopped smoking, started exercising, and began to eat right. After the changes, he had a much greater interest in sex and enjoys it more than ever.

Being able to dump the cigarettes is a real accomplishment -- especially when you consider how smoking can become intertwined with the intimacy of a relationship. Last year, for example, researchers at the University of Arizona began to study couples where at least one member of the relationship smoked.

The investigators began to realize that smoking actually became a method of subtle communication for members of the couples being studied. Lighting up gave clues to each partner that it was time to talk, time to give space, or even time to defend yourself because a world-class argument was about to begin.

The federally funded study is scheduled to go on for another year, and hopefully, will provide methods to help counsel couples how to recognize cigarettes as an abusive third member of their relationship. If couples are going to weed the habit from their lives, the researchers say they will have to find other ways to relate to each other, and more often than just during the familiar after-sex smoke.

And of course, as Jordan found, smoking can directly torpedo the sex, too.

"Smoking has a direct, negative effect on the sexuality of a man on every level," says Panayiotis M. Zavos, PhD, director of the Andrology Institute of America and professor of reproductive physiology and andrology at the University of Kentucky in Lexington.

From their work with couples being treated for infertility, Zavos and his fellow researchers have found that men's smoking had a significant and negative effect on the ability to conceive. But they also turned up a surprise: Smoking significantly diminished a man's sexual desire and satisfaction -- even for young men in their 20s and 30s.

The smokers reported having sex less than six times a month, whereas the nonsmoking men were having sex nearly twice as often. This difference is especially significant considering that these couples were actively trying to conceive. "In current research, we are trying to identify how and why tobacco use negatively impacts men's sexual performance. In my clinical experience, it does decrease performance. Sexual performance is more than just erectile function; it involves many of the systems of the body," says Zavos. "But when a man's ability to have sex decreases, his appetite for sex will generally follow."