The Way Everything Works on Instagram: "A period cycle begins on Day 1, which is the first day of bleeding. This happens because hormone levels (estrogen and progesterone) drop, signaling the uterus to shed the lining it built up the previous month. This lining exits the body as menstrual blood over several days, usually lasting until around Day 5–7. During this time, the body is essentially “resetting” for a new cycle. From Day 6 to Day 8, bleeding tapers off and the body shifts into the follic