I'm a woman in my mid-30s, and I've been sucking cock for almost half my life now, but I don't swallow. The reason I don't is that semen invariably has a laxative effect on me. I'd give a blowjob at night, and spend the next morning running to the bathroom. This was true with every guy I was with over a period of several years. I just wanted to ask, is this normal? Or at least not freakishly unusual? For the record, I don't have any other digestive issues. The few times I've mentioned it to other people, they looked at me like I was nuts. Hopefully you or your readers can reassure me that I'm not alone.

- Regular Until Next Swallow

My dear, dear RUNS. 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. And rather than wait until the next morning, her runs would come on about 90 minutes post-swallow.

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.

You, and the woman who called me years ago at the Institute, seem to be far more sensitive to them. So either spit, have guys come in a towel (or their hand), or swallow, and stay close to a bathroom the next day.

And in all seriousness, if there are more of you who have post-blowjob runs, I would love to hear from you: email me at DrDebby@MySexProfessor.com.