If there's one thing that almost every guy is an expert at, it's masturbation. After years of extensive, hands-on experience, you think you know everything there is to know. But according to the experts, maybe you don't. Here are some that may surprise you.

1. Masturbation doesn't have the health benefits that sex does. "It appears that not all orgasms are created equally," says Tobias S. Köhler, MD, MPH, an associate professor at Southern Illinois University School of Medicine in Springfield. Study after study shows that intercourse has all sorts of benefits for men -- for your blood pressure, heart and prostate health, pain, and more. You'd think that masturbation would, too. But it doesn't. Why would it make a difference whether you ejaculate during sex or on your own? No one's sure. But your body seems to respond differently. Even the makeup of semen is different if you masturbate instead of having sex. Still, does it really matter? Have you honestly been masturbating all these years only because you wanted to boost your prostate health? Didn't think so. But one study, Harvard’s Health Professional Followup, showed that Masturbation may help lower risk of prostate cancer.

2. Masturbation is not risk-free. Sure, it's low-risk. It's the safest form of sex possible. No one ever caught an STD from himself or made himself pregnant. But like other low-risk activities (chewing, walking), it still has some risks. Frequent or rough masturbation can cause minor skin irritation. Forcefully bending an erect penis can rupture the chambers that fill with blood, a rare but gruesome condition called penile fracture. Köhler has seen guys with it after vigorous masturbation. "Afterward, the penis looks like an eggplant," he says. "It's purple and swollen." Most men need surgery to repair it.