The science behind the cycle

This diagram maps the four phases of the menstrual cycle as a single, connected loop rather than a set of separate events. Estrogen and progesterone rise and fall in a precise, repeating sequence each month — estrogen builds through the follicular phase toward ovulation, then progesterone takes over through the luteal phase before both hormones drop and the cycle resets. That same rhythm drives the measurable shifts in body temperature, nervous system activity, and tissue density you saw in the interactive Cycle Explorer. Four phases, one continuous system — not four unrelated symptoms.