Consuming cold foods or beverages cools down the roof of your mouth and throat. Right behind those areas is a major artery that delivers blood to the brain, called the internal carotid artery. This means that eating cold things actually cools down the blood that’s flowing to and from your brain, says Greg McLauchlin, MD, Assistant Professor of Neurology at Baylor College of Medicine.
When the blood flowing to your brain gets too cold, your brain sets off an alarm — causing the headache known as brain freeze. This alarm warns you to stop or slow down the consumption of cold foods or beverages so that the temperature of the brain remains regulated.
This is why a brain freeze headache can hurt so badly: “Your brain has to send a signal that you cannot ignore. It can’t be a tickle. It can’t be an itch. It has to be something that makes you stop,” says McLauchlin.
In fact, brain freeze actually activates the trigeminal nerve, which is responsible for extreme pain. And if you’ve had that sudden, acute brain freeze sensation, you know that the pain is impossible to ignore.