Hot flashes, also known as hot flushes, are sudden feelings of warmth spreading through the body, often most pronounced in the face, neck and chest. They tend to last from 30 seconds to 10 minutes. Hot flashes are a common symptom of perimenopause and menopause. They occur when declining estrogen levels cause changes in the brain's thermostat that controls body temperature. When the thermostat malfunctions, it incorrectly senses that you are too hot, triggering sweating and flushing as the body tries to cool down. Some key facts about hot flashes: