Hot flashes occur in about 75 percent of menopausal women in the United States. The flashes most often begin in the perimenopausal period, although in some women they do not begin until after menopause. Hot flashes are almost always due to the menopause; other causes such as the carcinoid syndrome are rare (table 1) .
The prevalence, pathophysiology, and treatment of hot flashes will be reviewed here. Other menopausal symptoms and postmenopausal hormone therapy are discussed elsewhere. (See "Clinical manifestations and diagnosis of menopause" and "Menopausal hormone therapy: Benefits and risks" and "Treatment of menopausal symptoms with hormone therapy".)
Hot flashes typically begin as a sudden sensation of heat centered on the face and upper chest that rapidly becomes generalized. The sensation of heat lasts between two and four minutes, is often associated with profuse perspiration and occasionally palpitations, and is often followed by chills and shivering. Physiologic studies have determined that hot flashes represent thermoregulatory dysfunction; there is inappropriate peripheral vasodilatation with increased digital and cutaneous blood flow and perspiration resulting in rapid heat loss and a decrease in core body temperature below normal. Shivering then occurs as a normal mechanism to restore the core temperature to normal .
Hot flashes usually occur several times per day, although the range may be from only one or two each day to as many as one per hour during the day and night. They cause arousal from sleep, leading to sleep disturbances (see 'Sleep disturbance' below).
Prevalence — A systematic review of menopausal symptoms estimated that vasomotor symptoms occur in 14 to 51 percent of women before the perimenopausal transition, 35 to 50 percent in perimenopause, and 30 to 80 percent after menopause . It is generally believed that hot flashes do not occur in premenopausal women because serum estrogen concentrations are never very low, even during the menstrual period. However, the large observational SWAN study found that 20 percent of premenopausal women reported hot flashes [4,5].