Hot flashes are the most common symptom of menopause and perimenopause. It’s a sudden feeling of heat and sometimes a red, flushed face and sweating. We don’t know exactly what causes them, but they may be related to changes in circulation. Hot flashes start when blood vessels near the skin’s surface widen to cool off, making you break out in a sweat. Some women have a rapid heart rate or chills, too. When they happen while you sleep, they’re called night sweats. They can wake you up and may make it hard to get enough rest. A hot flush is a hot flash plus redness in your face and neck.