As predictable as your morning alarm clock, menstrual cramps show up every month a day or two before your period—totally uninvited, of course. As if the week of worrying about your tampon supply isn’t stressful enough, you have to deal with that crippling pain in your uterus, too. What’s the deal?
It’s actually pretty simple. All month long, your uterus has been building up a uterine lining (thanks to help from the hormone estrogen). This lining is where a fertilized egg would implant and set up shop, so your uterus is basically getting you all primed for pregnancy.
(Learn more about the female reproductive system here.)
Of course, you don’t get pregnant every month, so the uterus sheds that lining and starts over with each new menstrual cycle. To shed the lining, the uterus contracts, squeezes, and pushes out the uterine lining, which you see as your period. Those contractions, which can range from a dull throbbing to an intense spasm, are what you feel as menstrual cramps.
Some methods of birth control actually keep the uterine lining thin, which means you’ll have nothing to shed at the end of the cycle. In other words, you’ll be period- AND cramp-free. This is why many women with painful cramps, which is called primary dysmenorrhoea, take birth control specifically to treat the pain. (For example, here is how the IUD works, according to an ob-gyn.)
Cramps can certainly range in severity from person to person, but if your cramps are extremely painful, it might be a sign of something more serious. Conditions that might cause excessive period pain include endometriosis, fibroids, and pelvic inflammatory disease. These require more than just an ibuprofen and a warm bath, so speak to your doctor if your pain is intense.