There are three major types of headaches: tension (or stress), migraine, and cluster. A tension headache is caused by the tightening of muscles in the neck and head. A migraine headache occurs when blood vessels in the brain dilate (swell up). Cluster headaches are characterized by very severe pain.
Tension headaches are probably the most common form of the disorder. Nearly everyone has a tension headache from time to time. Migraine headaches are less common. Headaches can also be caused by other kinds of diseases, injuries, and disorders. Headaches of this kind are not discussed in this entry.