The Most Provocative Sex Science Stories

We've loved. We've learned. And we've had some of our sexual suspicions confirmed by scientific research. As 2009 comes to a close, LiveScience looks back at the year's nine most intriguing sex lessons.

Sex smells. A man's sweat smells different when he's sexually aroused — and women can tell the difference between the smell of sexual sweat and the regular stuff, according to a study in The Journal of Neuroscience.

Pulling out works. Well, most of the time. In a paper published in the June issue of Conception magazine, researchers claimed that withdrawal was "almost as effective as the male condom" when it came to pregnancy prevention (a failure rate of 18 percent, vs. the 17 percent failure rate of condoms).

Child's play. An Iowa State University study found that 25 percent of children — ranging in ages from 11 to 16 — in low-income households reported having sex. The average age of first intercourse for that group was 12.77.

Growing pains. According to a study from the University of Turin, penis extenders might work — a particular brand that used traction to gradually stretch the penis over time was found to increase flaccid members' length by almost one inch.

The pursuit of pleasure. Men who are very sexually active in their 20s and 30s — especially those who masturbate frequently — are at higher risk for prostate cancer, said researchers at the University of Nottingham. But that risk decreases as a man ages, and once he's in his 50s, even small levels of sexual activity can help protect him from the disease.