From around the age of 40, the amount of eggs in the ovaries decreases, and with it, the production of estrogen and progesterone gradually declines. This heralds the end of the fertile period.

The first signs of these hormonal changes—primarily due to the reduced progesterone—are bleeding irregularities. This often manifests itself in the form of annoying spotting, or irregular period intervals. In addition to the known symptoms such as sweating, irritability, or mood swings, women often suffer from listlessness, fatigue, and serious sleep disturbances.

It is only the gradual decline in estrogen production over the years that leads to a complete cessation of menstruation. On average, women are 50 years old when they have their last period — called menopause. However, many develop perimenopausal symptoms years before that. Due to the reduced estrogen, women eventually suffer from dry skin, especially in the vaginal area. For many, sexual intercourse becomes a painful chore.

Because hormones have a wide impact on organs, bodily functions and the psyche, symptoms aren't always associated strictly with the onset of menopause.  Some women complain of heart palpitations, dizziness, and circulatory problems; others suffer from joint pain or urinary incontinence. Increased water retention or fat accumulation in the abdominal area can also be unpleasant side effects of hormonal changes.