The single most frequent kind is the muscle-tension headache. When people are under stress, the muscles in their shoulders, neck, forehead, and scalp tend to tighten up. Prolonged stress can lead to prolonged muscle contraction, which causes muscle-tension headaches. Such headaches usually come gradually. They are characterized by dull, steady pain on both sides of the head and by feelings of tightness or pressure.

Most other types of headaches, including the severe migraine headaches, stem from changes in the blood supply to the head (Welch, 1993). Migraine headaches are intensely painful. They are caused by a two-stage process that begins with the constriction, or narrowing, of the arteries that supply blood to the brain. This constriction of the arteries often produces warning signals that a migraine headache is coming. These signals include dizziness, a flushed feeling, visual problems, and sometimes a sense of unusual odors. Little or no pain may be felt at this stage.

In the second stage of migraine headaches, the arteries dilate, or expand. The expanding arteries press on nerve endings that surround the arteries, producing the great pain associated with migraine headaches. The migraines themselves often include sensitivity to light, loss of appetite, nausea, vomiting, loss of balance, and significant changes in mood. Migraine headaches tend to come on suddenly and are characterized by intense throbbing on one side of the head. Migraine headaches may be caused by a change in air pressure (such as the change in atmospheric pressure that occurs before a thunderstorm), pollen, hormonal changes connected with menstruation, certain drugs, monosodium glutamate (MSG), chocolate, and aged cheeses (Brody, 1992). They can occur at any age but usually being when people are between the ages of 10 and 30.