I have scoured the Internet for years and I've never found an answer to this question, which isn't so much a problem as it is a matter of scientific inquiry.

I'm a straight woman who has been married to a wonderful guy for many years. We have a good sex life, and I very much enjoy blowing my spouse. I had a good sex life, too, before I met him, with a number of guys who I also enjoyed fellating. For the decade-long run of my singlehood, I swallowed the semen of a number of partners without incident.

Then I met my spouse. The first time I swallowed his stuff, I was hit—about 15 minutes later—with the most violent, embarrassing, uncontrollable case of the runs I'd ever had in my life. As I'm a curious person, I tried again to see if I'd get the same results. I did, and have, pretty much every time I've swallowed in the ten years of our marriage. (Every couple of years, I try again, just to see if things have changed. Nope.) In essence, the unique composition of my beloved's jizz turns the contents of my intestines to 100% liquid. (Fortunately, these episodes are painless—no cramping, just a lot of gurgling in my gut—and end almost as quickly as they begin.)

I've read about semen allergies, and how they can cause vaginal rashes, as well as difficulty in conceiving. I have no other symptoms beyond the sudden runs, and we were able to conceive a child pretty quickly after we started trying.

What gives?

Spit or Shit?

You've been scouring the wrong corners of the Internet, SOS, because this question was covered in a previous SLLOTD and in the column (im)proper—not by me, but by Dr. Debby Herbenick, one of my favorite guest experts.

Take it a way, Dr. H...

Believe it or not, you’re not the only person who’s found that swallowing semen has a laxative effect. There is at least one other woman on the planet who this happens to and, as luck would have it, she called me years ago out of the blue when I was sitting in my office at the Kinsey Institute. (What? You don’t get similar calls at your work? All in a day’s work, dear readers).

The woman from years ago had the most fantastic theory about why it happened to her: over time, noticing that this happened on the rare occasions she swallowed her husband’s semen, she decided that perhaps his sperm were trying to chase down her eggs in an effort to fertilize them, and then she thought once they realized they weren’t going to find her eggs in her GI tract, they jumped ship by making her have go to the bathroom.... I hated to break it to her, but there’s a much less exciting reason this can happen to some people when they swallow semen. An ob/gyn friend told me about the link years ago, when we were chatting over lunch at a meeting of the Vagina Society in New Zealand (vagina love has taken me to some amazing places).

So what is it?

Prostaglandins—substances made by the body and that the body is sensitive to. Semen contains prostaglandins—and prostaglandins can have a laxative effect on people. Related: If you’ve ever felt a little loosey goosey right before getting your period, that’s also thanks to prostaglandins (which spike just before your period, because the prostaglandins get the uterine muscles to contract, which then helps to shed the lining of the uterus, resulting in a menstrual period). Prostaglandins are also used to induce labor. So why don’t more semen swallowers find themselves running to the bathroom, post-blowjob? Fortunately, we’re not all so sensitive to prostaglandins. I don’t know why most people aren’t extra-sensitive but fortunately most of us aren’t or there would probably be a lot less swallowing in the world.

Dr. Herbenick is a research scientist at Indiana University, a sexual-health educator at the Kinsey Institute, and the author of numerous books. You really should be follow her on Twitter already: @DebbyHerbenick. Dr. Herbenick also hosts her own sex-advice podcast. Check out Kinsey Confidential.