Why do Periods Hurt? The science behind Menstrual Cramps. As much as periods are important, they can be very overwhelming. Several factors make periods daunting, including heavy flows, mood swings, food cravings, and worst of all, menstrual cramps. Dealing with menstrual cramps may be the hardest part of a monthly period for most women. But why? Let us understand why menstrual cramps happen in the first place. While we’re at it, we’ll go over ways to ease or prevent these cramps according to research.