Starting in perimenopause, your internal thermostat can go awry. The part of your brain responsible for sensing and controlling body heat overreacts to even slight changes in core body temp. This is likely due in part to estrogen withdrawal, but could also be due to extreme estrogen fluctuations. Most women report noticing triggers that make them have a hot flash—for example, spicy food, stress, or red wine.

Neurons in the brain are activated, and your brain sends out the signal that the body needs to cool down. In response, your veins, arteries, and capillaries widen to increase blood flow and dissipate heat. You may be over sensitive to drops in body temperature, too, which is why clamminess, shivering, and chills often follow hot flashes.

A hot flash can last from 1 to 15 minutes (usually closer to five) before your body temperature returns to the “comfortable” range. The process can continue for 7 to 9 years—that’s the average. It’s not uncommon to have hot flashes into your 70s or beyond. Scientists are working on finding a reliable predictor of when they will stop.