Why does ice cream give you brain freeze?

Brain freeze starts in your mouth, not your brain. When something very cold touches the roof of your mouth, the tiny blood vessels there tighten in the cold and then swell back open as they rewarm. Pain receptors sense that sudden swelling and send signals along the trigeminal nerve, one of the main nerves of the face. Because that same nerve also carries pain from your face, your brain gets confused about the address and feels the pain in your forehead. Doctors call this referred pain, the same phenomenon seen in heart attacks.

The pain is brief, often lasting just seconds, and it can strike on a freezing day as easily as a hot one, because what matters is the temperature of the food, not the weather. The same blood-vessel reaction, minus the pain, is why your cheeks flush after coming in from the cold.

Speed matters too. In 2002, a Canadian eighth-grade student, Maya Kaczorowski, tested 145 classmates with her father. Students told to wolf down their ice cream in under five seconds were about twice as likely to get brain freeze as those who took more than 30 seconds: 27 percent versus 13 percent. The study was published in the BMJ, a major medical journal, with its funding listed as 'an unrestricted grant from mum and dad'.