What Is Brain Freeze?

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Ice-cold substances hitting the back of the throat can cause blood vessels to expand and contract rapidly, resulting in a temporary but very painful headache.
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▼  You probably don't think of ice cream as a  pain-inducing substance, but enjoying those first few spoonfuls of the frozen treat too quickly might bring on a sudden, stabbing pain in the forehead known as "brain freeze."
The pain of brain freeze can begin within seconds of being exposed to cold temperatures, and the intensity of the pain peaks very quickly, often within seconds, said Dr. Stephanie Goldberg, a neurologist and headache specialist at Tufts Medical Center in Boston.
Why do you get it?
Brain freeze, also called an "ice-cream headache," is known in medical terms as a "cold-stimulus headache," Goldberg said. It's a common phenomenon that affects people of all ages, but doctors aren't quite sure why it happens.
For this type of headache, the main trigger is any kind of exposure to a significantly cold temperature, Goldberg said. It's not only caused by an internal trigger, like eating frozen treats too quickly; it can also be caused by an external trigger, such as going outside without a hat on a frigid day or diving into a very cold lake.
Brain freeze may start when a very cold substance — food or air, for example — hits the roof of the mouth or the back of the throat and stimulates blood vesselsand nerves in these temperature-sensitive areas.
A small study presented in 2012found that the sudden increase in blood flow and resulting increase in size of the anterior cerebral artery, a blood vessel located in the middle of the brain behind the eyes, may be responsible for brain freeze pain. The study found that when patients' brain freeze ended, the artery constricted and reduced blood flow, which is likely what caused the pain to disappear. The researchers said they suspect that an increase in pressure within the skull, brought on by increased blood flow to the head, is what causes the pain.
Another possible explanation for brain freeze is that a cold sensation activates an important nerve in the head and face, known as the trigeminal nerve. Once the trigeminal nerve is triggered, blood vessels inside the  headmomentarily tighten and constrict and then rapidly dilate or widen, resulting in a sudden feeling of pain, Goldberg told Live Science.
When the cold stimulus is removed, the blood vessels go back to their normal size and the pain tends to go away, Goldberg said.Despite being called "brain freeze," this brief episode of head pain doesn't cause permanent damage and isn't life-threatening.
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