Estrogen is the principal female sex hormone. Produced mainly by the ovaries, it controls the menstrual cycle and supports tissues throughout the body — bone, the heart and blood vessels, the brain, skin, and the vagina and urinary tract.
During perimenopause, estrogen fluctuates and then declines, which triggers symptoms such as hot flashes, sleep problems, mood changes, and vaginal dryness. Because estrogen also protects bone density and the heart, its loss raises longer-term health risks after menopause.
When symptoms are troublesome, estrogen can be replaced with hormone therapy, the most effective treatment for hot flashes.