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It’s happened to the best of us: You’re in the middle of a long-awaited vacation only to realize... you haven’t pooped in days. And when you do try to go… it’s just not happening.

Congratulations: You are experiencing traveler’s constipation. It’s why I don’t go places. It’s the blockage some people feel while traveling, and it can be a very literal pain in the butt.

Thankfully, there are at least some things you can do to avoid it. And if nothing else… you’re definitely not alone. And if you’d like to hear about one thing someone I know tried to do to avoid it, you can be a Patron on Patreon, where we just had a long little conversation about it.

Traveler’s constipation is an all too familiar occurrence for some, but it might get under-reported since most people aren’t super excited to talk about it. One 2008 study, published in the journal Digestive Diseases and Sciences, found that 9% of 68 international travelers had developed it. Well, now I feel like I’m exceptional...

But a 2003 study from the American Journal of Gastroenterology reported a much higher number: 38% of 65 subjects. It’s likely that the numbers vary from group to group, because like all kinds of constipation, traveler’s constipation has a bunch of potential causes. Like, traveling even a few towns away can lead to behavioral changes that affect regularity.

For example, loading up on caffeine during the drive or having that extra alcoholic drink — or three — on the beach can lead to dehydration, which contributes to constipation. We also tend to eat more foods rich in carbs and fat while on holiday, and to sit a lot more. Physical activity helps stimulate gut movement, so plopping down in a car or plane for hours can cause your bowels to creep to a halt.

Add in a little stress over making it to the airport or loading up the car on time, and you’ve got yourself a perfect recipe for blockage. Can’t say I’d give this particular recipe a fantastic rating. 1 out of 5 stars. Many cases of traveler’s constipation, though, are often associated with jet lag, which is why it might be reported in surveys by international travelers.

Jet lag is caused by disrupting your circadian rhythm, or your body’s internal clock. When you travel across time zones, you can end up with a whole host of side effects including sleepiness, discomfort, and — you guessed it — constipation. This all happens thanks to a structure in your brain called the suprachiasmatic nucleus, or SCN.

It’s located in the hypothalamus, a little spot near the middle of your brain, and sends out signals that maintain your sleep-wake cycle. The SCN is influenced by the hormone melatonin, and also by the levels of light you see. So if you travel and suddenly start sleeping at odd times or seeing daylight when your body thinks it should be dark, signals from the SCN get thrown out of whack.

And voila, jet lag. Besides regulating your circadian rhythm, the SCN also sends signals throughout your body, including to neurons in your gastrointestinal tract. The SCN and GI tract actually trade signals back and forth all day to synchronize the timing of things like pooping.

And when these messages get jumbled up by jet lag, your gut just kind of slows down until the SCN can get your body’s rhythm back on track. So if you’re having some trouble with your number two the next time you hit up Disney. World or take an international flight, it’s okay: It happens, and it’s nothing to be embarrassed about.

It happens to me every time. Things you can try: cutting back on those Mickey-shaped ice creams, taking a long walk, or talking to your doctor or pharmacist about it. And just remember, this too shall pass.

Thanks for asking, and thanks as always to our patrons on Patreon! We really appreciate your support and are thankful for your curiosity and wonder about the world. If you want to submit a question for us, though it’s probably not going to be as good as this one, you can do that at patreon.com/scishow. [♪ OUTRO].