Estrogen controls development and maintenance of the female reproductive system and secondary sexual characteristics, including breast development and pubic hair. It regulates the menstrual cycle and fertility, supports bone density, affects fat distribution and skin elasticity, and influences mood and libido. Estrogen also impacts cardiovascular health by helping maintain healthy cholesterol levels and blood vessel function.

Low estrogen can cause irregular or absent periods, hot flashes and night sweats, vaginal dryness and painful sex, urinary frequency or infections, low libido, mood swings, anxiety or depression, sleep problems and fatigue, brain fog or memory issues, dry skin and hair, and increased risk of bone loss leading to fractures. Symptoms vary by age and cause.

High estrogen in a girl can cause early or rapid puberty, breast development, irregular or heavy periods, bloating, weight gain, acne, mood swings and headaches. It may disrupt menstrual cycles and increase risk of ovarian cysts or other hormonal imbalances. Persistent or severe symptoms warrant evaluation by a healthcare professional to identify causes and guide treatment.

Estrogen does not directly cause major weight gain. Fluctuations—during puberty, the menstrual cycle, pregnancy, or menopause—can change appetite, fluid retention, metabolism and fat distribution. Low estrogen in menopause is linked to increased central (abdominal) fat. Hormone therapy may cause modest weight or fluid changes, but most effects reflect redistribution of fat and water rather than large gains in body fat.

Estrogen promotes breast development by stimulating ductal growth and increasing fat deposition, so higher estrogen (puberty, pregnancy, hormone therapy) often enlarges breasts. Magnitude varies with genetics, body weight, age, and other hormones (progesterone). Combined contraceptives or HRT can cause modest increases; transgender feminizing hormones produce some growth but often not to desired size. Changes may take months to years.

When estrogen is high, many women feel more energetic, confident, socially outgoing, with improved mood, sharper concentration, and increased libido. Physically they may notice breast fullness or tenderness, bloating, mild water retention, and sometimes headaches or migraines. In some people, excess estrogen can also cause irritability, anxiety, or heavier menstrual bleeding.