Hot flashes — a defining symptom of menopause — can seriously interrupt your life. A hot flash can occur without warning, creating unpleasant episodes especially if your face flushes, or if you routinely perspire through your clothes. As night sweats, they can wake you from a sound sleep, with your pajamas and sheets soaked through. When you have a hot flash, the temperature regulating area within your brain — in the hypothalamus — is deceived into trying to get rid of extra body heat. The hypothalamus sends cool-down signals telling your blood vessels to dilate, your heart rate to increase, and your sweat glands to open up wide.