When something cold touches the roof of your mouth (your palate), the sudden temperature change of the tissue stimulates nerves to cause rapid dilation and swelling of blood vessels. This is an attempt to direct blood to the area and warm it back up. The dilation of the blood vessels triggers pain receptors, which release pain-causing prostaglandins, increase sensitivity to further pain, and produce inflammation while sending signals through the trigeminal nerve to alert the brain to the problem. Because the trigeminal nerve also senses facial pain, the brain interprets the pain signal as coming from the forehead. This is called 'referred pain' since the cause of the pain is in a different location from where you feel it. Brain freeze typically hits about 10 seconds after chilling your palate and lasts about half a minute. Only a third of people experience brain freeze from eating something cold, though most people are susceptible to a related headache from sudden exposure to a very cold climate.
How to Prevent and Treat Brain Freeze
It's sudden chilling or a cycle of chilling and warming that stimulates the nerve and causes pain, so eating ice cream slowly is less likely to cause brain freeze than wolfing it down. If you are eating or drinking something cold, it also helps to keep your mouth cold rather than allow it to warm up. However, one of the quickest ways to alleviate the pain of brain freeze is to warm your palate with your tongue. Just be sure not to follow that remedy with another scoop of ice cream.