A migraine headache is a form of vascular (blood vessels) headache. Migraine headache is caused by a combination of vasodilatation (enlargement of blood vessels) and the release of chemicals from nerve fibers that coil around the blood vessels. During a migraine attack, the temporal artery enlarges. (The temporal artery is an artery that lies on the outside of the skull just under the skin of the temple.) Enlargement of the temporal artery stretches the nerves that coil around the artery and causes the nerves to release chemicals. The chemicals cause inflammation, pain, and further enlargement of the artery. The increasing enlargement of the artery magnifies the pain.
The above results in periodic attacks of headaches on one or both sides of the head. These may be accompanied by nausea, vomiting, increased sensitivity of the eyes to light (photophobia) with visual disturbance and flashes (aura), increased sensitivity to sound (phonophobia), dizziness, blurred vision, cognitive disturbances, and other symptoms. Some migraines have these symptoms but do not include headache, and migraines may or may not be preceded by an aura.