No one knows, exactly. Body chemistry, hormones, and environment all may have an effect, but the exact cause (or combination of causes) has yet to be identified.

Scientists currently are looking at genetics as a factor in some forms of migraine. As evidence that heredity does play an important role, note that up to 70% to 80% of people with migraine have a family history of the disease.

Migraine may be a response to “triggers” (such as certain foods, hormones, or environmental factors)—factors that cause nerves to become sensitized and blood vessels to swell. This response may lead to a migraine.