When you're having sex, you pretty much know the outcome—much like you know that popping open a bottle of champagne will end with it fizzing over. For some men, at some times, this isn't true (the sex, not the champagne).

It's a condition called "retrograde ejaculation," when orgasm does not include ejaculation. So ... how exactly can you fire a shot without, well, firing anything?

First, an anatomy lesson: Your prostate is connected to the penis on one end and the bladder and seminal vesicle on the other. When you’re ready to ejaculate, your semen travels out the seminal vesicle and into the prostate, where it reaches a fork in the road: one path leading up to the bladder and the other leading out to the penis.

Normally when a guy finishes, the smooth muscle in the bladder neck contracts, forcing the ejaculate to make its way out the penis. With retrograde ejaculation, though, this muscle doesn’t contract, and the ejaculate takes the path of least resistance—up into the bladder instead of out the penis.

While that sounds uncomfortable, guys can’t even feel it, says Kevin Campbell, M.D., a physician at The Urology Group in Cincinnati, Ohio. Plus, your body will flush out the semen next time you pee, so it isn’t harming your health.

That begs the question: If it doesn’t hurt, do you even need to worry about it?

If the reason behind your dry finish is obvious—and it usually is—then no: Retrograde ejaculate is a common side effect for men who are diabetic, have had prostate surgery, or are on prostate medication, because all three of these affect that smooth muscle’s ability to close off the path.

If none of these reasons apply, you should see a urologist. “One cause for retrograde ejaculation in healthy guys is an obstruction, like a blockage in the urethra,” Dr. Campbell explains. If that’s the case, you’ll probably also have a slow urine stream.

It can also be a sign of a neurological condition like multiple sclerosis, since nerve damage could affect your muscle’s ability to keep the bladder valve shut.

The time not to worry about a fading finish: when you're enjoying back-to-back sessions. “The seminal vesicles that store semen can only hold so much, so if you have sex multiple times a day, your body doesn’t have enough time to build its supply back up,” Dr. Campbell explains. “At some point, you’ll have used up all your seminal fluid, and nothing will come out with your orgasm.”

If you’re getting down with days in between and you notice your semen is in short supply or nonexistent, check in with your doc. “It’s not urgent, but it’s not something to be brushed off either,” Dr. Campbell adds.

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Rachael Schultz Rachael Schultz is a freelance writer who focuses primarily on why our bodies and brains work the way they do, and how we can optimize both (without losing our sanity).

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