Norman Harden is a neurologist in charge of the Center for Pain Studies at the Rehabilitation Institute of Chicago. He provides the following answer.
Narrowly defined, headache is pain in the head or face, and sometimes also includes pain in the upper neck. Pain sensitive structures in the head and face include the skin, bone and structures in the eyes, ears, nose and mouth. Also, the large blood vessels of the head are exquisitely sensitive and these are the principal organs causing pain in vascular headaches, such as migraines. The jaw hinge (called the temporomandibular joint) and the teeth can also generate headache. The brain itself is not pain sensitive and is not a source of head pain.
The most common type of headache is the tension or muscle contraction type, which is frequently caused by spasms in the neck muscles and the muscles of mastication (chewing). This type of headache is usually treated easily by over-the-counter medications. More intense headaches are caused by unknown mechanisms. Most theories of vascular headache involve the relationship between the nerves and the blood vessels, both of which can be sensitive.
Image: American Council for Headache Education
In people who are prone to migraine, these headaches can be triggered by a multitude of causes, including diet, stress, lights, strong smells and other environmental conditions (either external or internal). Once the migraine process has started, it usually requires medication to stop the headache. There are many other specific, less common headache diagnoses, such as cluster headaches and neuralgia, or nerve damage headaches.
All of these headaches have specific treatments, both pharmacological and non-pharmacological (for instance, relaxation or biofeedback techniques). Additionally, there are new medications being developed on an almost monthly basis, all of which hold promise for treating these most painful of headaches. Anyone who suffers from headaches and who has given up on medical treatments should return to his or her family physician and inquire about the new prospects for substantial relief.