ELI5: What causes back pain during a menstrual cycle?

Back pain during a menstrual cycle happens because natural body chemicals make the womb squeeze tight, and that squeezing feeling spreads to the lower back muscles nearby.

Inside a woman's body, the uterus (or womb) is like a cozy little room that builds a soft lining each month. When the body does not need this soft lining, it has to clean the room out. To do this, the body sends out tiny chemical messengers called prostaglandins.

You can think of prostaglandins like a team of little coaches telling the womb to do jumping jacks. They tell the muscles to squeeze and push the old lining out.

Sometimes, these little chemical coaches are a bit too loud and enthusiastic:

• Squeezing too hard: The womb squeezes so strongly that it presses on nearby blood vessels. This makes the muscles around the tummy and hips tired and achy.
• Spilling over: Because the womb and the lower back share the exact same neighborhood, the heavy squeezing feeling does not stay in one place. It travels backward to the muscles in the lower spine.
• Shared nerve highways: The body uses the same "telephone wires" (nerves) to send messages from both the womb and the lower back up to the brain. When the womb sends a signal that it is working hard, the brain gets a little confused and feels the ache in the back, too. This is called referred pain.