What causes hot flashes is not precisely known. Loss of estrogen, which is no longer produced by the ovaries after menopause, is thought to play a role, but the increase in hormones from the pituitary gland, which occurs when estrogen is no longer produced, may also be important. This pulsatile release may be the cause of intermittent hot flashes, which come on suddenly, last for a few minutes, and then rapidly fade away.
Hot flashes can develop immediately after estrogen stops being produced.
In fact, women who have had their ovaries removed, so that the source of estrogen disappears abruptly, may have hot flashes as soon as they awaken from anesthesia. For this reason, many gynecologists start prescribing hormone replacement immediately after surgery. The other effects of estrogen loss take place more slowly, often over a period of years. These include thinning of the membranes in the vagina, thinning of the lining of the uterus, loss of breast size, osteoporosis, and changes in cholesterol levels. These changes occur gradually and can have serious long-term effects.