Migraines happen when the brain and nervous system start sending abnormal pain signals. Sometimes, a wave of electrical activity called cortical spreading depression spreads across the brain, which can cause the visual effects or “auras” some people notice before a migraine. At the same time, blood vessels in the brain can constrict and then widen, releasing chemicals called neuropeptides, like CGRP, that irritate nearby nerves and cause the throbbing pain people feel. Changes in neurotransmitters, like low serotonin or high glutamate, can make the nerves more sensitive to pain and less able to block it.

The trigeminal nerve, a major nerve in the face and head, also becomes active during migraines. This releases more inflammatory chemicals around the brain and its protective layers, which can cause nausea, vomiting, and sensitivity to light or sound. Genetics play a role too, making some people more likely to get migraines, and triggers like stress, certain foods, or lack of sleep can set off an attack. Overall, migraines happen because the brain, nerves, blood vessels, and chemicals all interact in ways that make the nervous system overreact to signals.