For all the attention they direct below the belt, most men actually know very little about their penises.

 Here’s the knowledge you need to keep yours healthy, strong, and ready for action, for life.

Fact 1: Smoking can shorten your penis by as much as a centimeter. Erections are all about good blood flow, and lighting up calcifies blood vessels, stifling erectile circulation. So even if you don’t care all that much about your lungs or dying young, spare the little guy.

Fact 2: Doctors can now grow skin for burn victims using the foreskins of circumcised infants. One foreskin can produce 23,000 square meters, which would be enough to tarp every Major League infield with human flesh.

Fact 3: An enlarged prostate gland can cause both erectile dysfunction and premature ejaculation. If you have an unexplained case of either, your doctor’s looking forward to checking your prostate. Even if you’re not.

Fact 4: The average male orgasm lasts 6 seconds. Women get 23 seconds. Which means if women were really interested in equality, they’d make sure men have four orgasms for every one of theirs?

Fact 5: The oldest known species with a penis is a hard-shelled sea creature called Colymbosathon ecplecticos. That’s Greek for “amazing swimmer with large penis.” Which officially supplants Buck Naked as the best porn name, ever?

Fact 6: Circumcised foreskin can be reconstructed. Movable skin on the shaft of the penis is pulled toward the tip and set in place with tape. Later, doctors apply plastic rings, caps, and weights. Years can pass until complete coverage is attained.

Fact 7: Only one man in 400 is flexible enough to give himself oral pleasure. It’s estimated, however, that all 400 have given it their best shot at some point.

Fact 8: There are two types of penises. One kind expands and lengthens when becoming erect (a grower). The other appears big most of the time, but doesn’t get much bigger after achieving erection (a shower).

Fact 9: An international Men’s Health survey reports that 79 percent of men have growers, 21 percent have showers.

Fact 10: German researchers say the average intercourse lasts 2 minutes, 50 seconds, yet women perceive it as lasting 5 minutes, 30 seconds.

Fact 11: Turns out size does matter: The longer your penis, the better “semen displacement” you’ll achieve when having sex with a woman flush with competing sperm. That’s according to researchers at the State University of New York, who used artificial phalluses (ahem) to test the “scooping” mechanism of the penis’s coronal ridge.

Fact 12: The penis that’s been enjoyed by the most women could be that of King Fatefehi of Tonga, who supposedly deflowered 37,800 women between the years 1770 and 1784—that’s about seven virgins a day.

Fact 13: Better-looking men may have stronger sperm. Spanish researchers showed women photos of guys who had good, average, and lousy sperm—and told them to pick the handsomest men. The women chose the best sperm producers most often.

Fact 14: No brain is necessary for ejaculation. That order comes from the spinal cord. Finding a living vessel for said ejaculation, however, takes hours of careful thought and, often, considerable amounts of alcohol.

Fact 15: The most common cause of penile rupture: vigorous masturbation. Some risks are just not worth taking.

Red Pepper