One of the most common symptoms of menopause and perimenopause, about 75% of all women experience hot flashes which are sudden, brief, periodic increases in their body temperature. Usually hot flashes start before a woman’s last period and for 80% of women, hot flashes occur for two years or less. Although a small percentage of women may experience hot flashes for more than two years. These flashes seem to be directly related to decreasing levels of oestrogen and vary in frequency and intensity for each woman. In addition to the increase in the temperature of the skin, a hot flash may cause an increase in a woman's heart rate. This causes sudden perspiration as the body tries to reduce its temperature. This symptom may also be accompanied by heart palpitations and dizziness. Hot flashes that happen at night are called night sweats. A woman may wake up drenched in sweat and have to change her night clothes and sheets. Hormone therapy has been shown to relieve some of the discomfort of hot flashes for many women.