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 are a common symptom of perimenopause and menopause. What causes hot flashes? They are caused by decreasing levels of the female hormone estrogen during perimenopause and menopause. As estrogen declines, the hypothalamus - the area of the brain responsible for controlling body temperature - becomes more sensitive to small changes in temperature. This triggers the hypothalamus to release more hormones that make blood vessels dilate and heat leave the body, causing hot flashes. Some key points about hot flashes: