Hormones are chemical messengers produced by glands in the endocrine system. They travel through the bloodstream to tissues and organs, regulating key processes such as growth, metabolism, reproduction, mood, and the maintenance of homeostasis.

Perimenopause is the transitional period before menopause, during which the ovaries gradually reduce hormone production. It often begins in the late 30s or 40s and precedes the final menstrual period by several years. Hormone levels (especially estrogen and progesterone) become erratic — sometimes high, sometimes low — leading to fluctuating symptoms and unpredictable menstrual cycles.

Menopause is defined as the point in time when menstrual periods have stopped for 12 consecutive months. This reflects the ovaries’ cessation of hormone (primarily estrogen and progesterone) production. Menopause typically occurs between ages 45–55, though it may occur earlier (e.g. surgically induced). 

Andropause refers to the age-associated, gradual decline in male sex hormones — especially testosterone — over decades. Unlike menopause in women, andropause is not a sudden shutdown; hormone levels slowly decrease (often ~1% per year after age 30) and clinical symptoms may or may not appear depending on individual physiology.