Ice cream, milkshakes, snow cones, frozen Cokes—if icy concoctions cause a stabbing or searing pain across your forehead, you’re not alone: Some 40 to 80 percent of people occasionally get "brain freeze" after eating or drinking something frigid. While your brain doesn’t really freeze, studies show that the temperature in your head does drop when you eat something very cold over a few minutes.

Up to 93 percent of migraine sufferers say they also get ice cream headaches. But even the normally headache-free often suffer a brain freeze attack at the local Baskin-Robbins. The pain usually peaks in a minute, and then quickly fades. Theories abound about what, exactly, causes the stabbing pain. Some say the headache is a referred pain from iced nerves in the palate and throat. Others say that blood vessels in the mouth and throat, constricted by the cold, cause blood vessels in the rest of the head to expand, triggering a headache.

However, many have noted that they don’t have to be eating anything to get brain freeze. A faceful of snow during a winter snowball fight, a blast of icy wind on an exposed forehead, or a slap in the face by a cold ocean wave can produce the same brief, excruciating pain as chugging a milkshake.

One researcher used an ultrasound machine to track blood flow in the brain during ice cream headaches. He found that blood flow temporarily decreased, indicating cerebral arteries were constricting. But no one knows whether the constriction results from chilled blood flowing through the neck to the brain, or from a signal sent by chilled nerves in the palate and throat.

In 2002, an eighth-grade student named Maya Kaczorowski had her own brain freeze experiment published in the British Medical Journal. Maya recruited 145 kids to participate in ice cream-eating sessions. Some ate small amounts of ice cream quickly (in less than 5 seconds); others indulged more slowly.

The result: About 13 percent of the students in the slow group got ice cream headaches, while more than twice as many of the fast eaters experienced the icy pains. And nearly 80 percent reported getting brain freeze sometime in the past. (Read Maya’s full report at http://bmj.bmjjournals.com/cgi/content/full/325/7378/1445.)

More recently, researchers in Japan used the slurpee method to induce headaches in their subjects. The results were presented at the October 2005 meeting of the American Society of Anesthesiologists. Volunteers were asked to eat a whopping 3/4th lb. of shaved ice over 10 minutes. About 2.5 minutes into the experiment, volunteers began to get severe headaches.

During the headaches, the volunteers’ ear temperatures dropped, but armpit temperatures stayed the same. So cooling the throat, and thus the carotid arteries in the neck, may cool the brain without producing a big change in body or heart temperature. That could be a way, the researchers suggest, to protect the brain without hurting the heart while doing life-saving CPR.