Menopause is not a disease but a physiological stage in a woman's life that coincides with the end of her fertility. Specifically, menopause is defined as the permanent cessation of menstrual cycles resulting from the loss of ovarian follicular function; it is diagnosed retrospectively after 12 consecutive months of amenorrhea (absence of menstruation). Menopause occurs because, as a woman ages, the ovaries stop producing estrogen and progesterone. In the years leading up to menopause, the production of estrogen and progesterone begins to decline, and menstruation and ovulation become less frequent before eventually ceasing altogether; at that point, natural conception is no longer possible. It generally occurs between the ages of 45 and 55, though early or late onset is not uncommon. The drop in estrogen levels during menopause can lead to various symptoms, including hot flashes, sweating, mood swings and irritability, decreased libido, sleep disturbances, and physical and mental fatigue. Hot flashes and sweating are among the most characteristic symptoms of menopause. Hot flashes affect 75% to 85% of women and usually appear before menstruation ceases; they generally last a few minutes and manifest as a sensation of heat—felt most intensely in the face, neck, and chest—that may be accompanied by episodes of heavy sweating. Furthermore, many women are unaware that declining estrogen levels can lead to less obvious but more dangerous conditions, such as osteoporosis, hypercholesterolemia, and dyslipidemia.