Scientists used to think that migraines were caused by dilation or constriction of the blood vessels of the brain and meninges — the protective connective tissue that surrounds the brain. However, recent evidence suggests that migraines may be caused by a defect in certain populations of cells in the brain itself — called neurons — that makes them hyper-excitable. The site of the defective neurons, and thus the root of migraine pain,  is still a matter of debate with some researchers believing the culprit cells are in the cerebral cortex of  the brain and others thinking they are in the brainstem. Newer research suggests that aberrant activity in one of these brain regions fools a part of the brain called the trigeminal nucleus — which is responsible for sensing pain in the blood vessels that surround the brain — into thinking the vessels are registering pain, even when there is nothing wrong with them.

It is unknown what causes neurons to become hyper-excitable in some people but not others. Genetic factors are likely involved, because headache disorders — including migraines — seem to run in families. There are probably several genes involved that make someone susceptible to migraines but do not guarantee they will experience them. 

For people who experience migraines, there are often triggers that can set off symptoms. What triggers a migraine in one person may not necessarily be a trigger for someone else. Some common triggers include:

• hormonal changes (in women)  
• certain foods including: alcohol, aged cheeses, chocolate, and caffeine; foods that are fermented, pickled,  marinated, canned, or processed; and foods containing aspartame, nitrites or monosodium glutamate (MSG)
• skipping meals or fasting
• stress
• bright lights
• strong smells
• changes in sleep/wake pattern
• intense physical exertion
• changes in the environment or season
• certain medications