Robert Smith is professor emeritus and founding director of the department of family medicine at the University of Cincinnati and the founder of the University of Cincinnati Headache Center. He provides the following explanation:
Ice cream headache is a fairly common condition and has been commented on in the medical literature since the 1850s. The cause is still a matter of some debate, however. Holding ice or a large amount of ice cream in the mouth, or swallowing a mouthful of cold food or drink, may cause discomfort or pain in the palate and throat. In some people it also causes headache. Reports on how frequently this occurs vary between 30 and 40 percent for individuals who do not normally suffer from headaches. There is general agreement that migraine sufferers, particularly those who get severe attacks, are more prone to suffer from ice cream headaches as well. In one study, 85 percent of migraine sufferers experienced this form of headache.
A headache develops as a frozen treat is eaten; the pain is often reported as rapid in onset, severe, located in the middle of the forehead or in both temples, and tends to last no longer than five minutes. It may be one-sided in patients who get migraines and it may trigger a full-blown bout of migraine in these patients, though this occurs rarely.
The term "ice cream headache" falls into the group of short-term headaches known as cold-stimulus headaches. Both the World Health Organization and the International Headache Society have recognized them as benign headaches that do not indicate the presence of underlying disease and do not represent any health hazard to an individual. The condition is easily prevented by avoiding rapid swallowing of large mouthfuls of ice cream or ice cold drinks.
Exposure of the bare head to subzero temperatures or diving into ice cold water may also cause headache, probably from excessive stimulation of temperature-sensitive nerve endings in the skin of the scalp and face. Repeated exposure to such stimuli may raise the threshold to the cold stimulus, decreasing skin sensitivity and reducing the likelihood of headache. There have been no reports of any ice cream adaptation studies, but there should be no difficulty in finding willing volunteers.
The mechanisms underlying ice cream headache are not fully understood. The palate and throat have a liberal supply of blood vessels and nerves. Ice cream applied to the mucous membrane of the palate and throat stimulates blood vessels, nerves and muscle fibers and causes local discomfort. But a broader distribution of stimuli from the area of contact is required to generate headache.
In recent years researchers have learned much about how headache arises, resulting in major advances in both the treatment and prevention of migraine. The branches of the trigeminal and upper cervical nerves provide sensation for the face and scalp and are involved in the production of headaches such as migraine, tension and cluster headaches. Not as much is known about the less-disabling ice cream headache. The fact that the latter is more likely to occur in migraine sufferers, however, suggests that local throat stimulation penetrates deeply into the nervous system, making contact with central trigeminal pathways that cause headache. More studies are needed to clarify the picture. Fortunately, in the meantime, all that people vulnerable to the condition need to do to avoid the problem is exercise caution while eating ice cream.