Dear Alice,

I was just wondering what happens to semen after it has been ejaculated into a woman's vagina. Does it just stay there until it dies, or does it seep out? If it stays in, what happens to it once it dies?

Thanks,
Prude and Wondering

Dear Prude and Wondering,

Good guesses! Semen (the fluid that carries sperm), if ejaculated into the vagina and not blocked by a barrier contraceptive method such as a condom, could either disintegrate, travel farther into the vagina, seep out and eventually dry up, or a combination of these options.

Most sperm don't even make it very far! The female reproductive system has a series of mechanisms to limit exposure to foreign bodies. First, the semen might succumb to gravity and seep out of the vagina. Some people opt to use panty liners when they're out and about to help absorb the moisture. For the semen that stays inside the body, since the vagina is naturally acidic, it creates a hostile environment for the sperm. Further, the cervical mucus (mucus discharged from the cervix, which is a donut shaped structure separating the uterus and vagina) filters out any damaged sperm, and many of them suffer from stresses along the way due to the environment, causing them to break down. Only a small percentage make the longer trek. 

For the sperm that go deeper into the vagina, their next step is sometimes to swim through a tiny hole in the cervix. Next, the surviving sperm might swim through the uterus and up into the fallopian tubes, the thin tubes that transport eggs from the ovaries to the uterus. It’s in the fallopian tubes that a sperm cell potentially fertilizes an egg cell, which may lead to pregnancy. Semen that remains in the body will carry sperm that may survive for approximately six days. 

For semen that finds itself outside the vagina, when semen evaporates in the open air, the sperm that it contains dies. It’s difficult to determine the exact or approximate amount of time (i.e., seconds, minutes, hours) it takes for semen to dry up, ensuring sperm are also dead, once outside the body. The exact time is difficult to pin down since it depends on many factors, such as the surrounding environment (i.e., humidity, temperature), body temperature, consistency (if semen is spread thickly or thinly on the body), and location (where the semen is on the body).  

It's great that you're seeking a better understanding of what happens after ejaculation, as knowing under what conditions sperm and egg may be more likely to meet can help inform what safer sex practices are put into place if pregnancy prevention is of interest. Further, it could also help to inform what types of STI prevention may be of interest. 

Hope this answer helps you solve the mystery!

Alice!

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