Period pain affects hundreds of millions of people. Anywhere from 50 to 90% of people who menstruate deal with painful abdominal or pelvic cramps during their period. Individual experiences can vary, from mild discomfort, to throbbing aches, to contraction-like cramps that rival the pain of labor. So, why do menstrual cramps hurt so much? Chen X. Chen explains this surprisingly common experience. Lesson by Chen X. Chen, directed by Caitlin McCarthy.