Beyond reproduction, progesterone affects several systems in the body, and this chapter explains each in turn. It covers bone health, including the hormone's part in calcium absorption and bone formation, and its effects on skin through collagen production and hydration. The chapter then looks at heart health, describing how progesterone can support cholesterol balance, blood pressure and blood vessel function, and at mood, where steady levels can encourage calm and ease anxiety. It explains how progesterone is used in many contraceptive methods, and closes with signs that levels may be out of balance, from irregular periods and mood swings to fatigue and bloating.