Why do we get ice cream headaches?

The scientific name for brain freeze is sphenopalatine ganglioneuralgia. It occurs when cold food or drink rapidly chills the roof of the mouth and the back of the throat, causing blood vessels there to quickly narrow and then widen again. This sudden change is detected by nerves, especially the trigeminal nerve, which relays sensations from the face to the brain. Because this nerve also serves the forehead, the brain misinterprets the signal and you feel a sharp, stabbing pain in your head rather than your mouth, a phenomenon called referred pain. The ache usually lasts only seconds and can be eased by warming the roof of the mouth with your tongue.