Migraines are caused by abnormal brain activity. This abnormal activity may be triggered by a number of factors. Although the exact process in which this occurs is unknown, the disorder appears to involve blood vessels, nerve pathways and chemicals in the brain.

Some researchers believe migraines are caused by imbalances in brain chemicals such as serotonin (a neurotransmitter that controls pain signals traveling through the trigeminal nerve) or changes in the trigeminal nerve, which carries sensory stimuli to the brain from the face, teeth and tongue. Others believe that migraines are due to central sensitization, which means that pain centers feel pain without any painful stimulus (allodynia).

Serotonin levels drop during a migraine. Many researchers think this triggers the trigeminal nerve to release substances known as neuropeptides. Once released, the neuropeptides travel to the brain’s surface, where they cause swelling and inflammation of blood vessels.  This results in head pain. Low levels of magnesium, a mineral involved in nerve cell function, may also play a role.

Factors that may trigger a migraine include:

• Sensory stimulus, such as bright lights, loud noises or certain odors
  
  
• Stress (physical or emotional)
  
  
• Depression
  
  
• Changes in sleep patterns, including too little or too much sleep
  
  
• Smoking or exposure to secondhand smoke
  
  
• Skipping or delaying meals
  
  
• Alcohol or caffeine
  
  
• Intense physical activity
  
  
• Tension headaches
  
  
• Medications that cause the blood vessels to swell (vasodilators), including some blood pressure medications
  
  
• Frequent use of pain medication (rebound withdrawal headaches)
  
  
• Allergic reactions
  
  
• Environmental changes, such as changes in weather, altitude level, barometric pressure or time zone
  
  
• Hormonal changes, including those caused by menstruation, pregnancy, menopause, birth control pills or hormone replacement therapy

Although responses vary among individuals, certain foods can trigger migraines as well, including:

• Chocolate
  
  
• Peanut butter and nuts
  
  
• Certain fruits (e.g., avocado, banana, citrus fruits)
  
  
• Onions
  
  
• Dairy products
  
  
• Baked goods
  
  
• Fermented foods
  
  
• Pickled and marinated foods
  
  
• Foods containing monosodium glutamate (MSG) or  nitrates (hot dogs, bacon)
  
  
• Foods containing the amino acid tyramine (e.g., red wine, aged cheese, smoked fish, chicken livers, figs and some beans)

A number of factors appear to make a person more likely to develop migraines. These risk factors include:

• Age. According to the National Headache Foundation (NHF), migraines occur most often between the ages of 15 and 55.
  
  
• Sex. The NHF estimates that women are affected with migraines three times as often as men.
  
  
• Family history. Migraines are more likely to occur in people with migraine sufferers in their immediate family, such as a parent or sibling. According to the NHF, between 70 and 80 percent of migraine sufferers have a family history of migraines.

Some studies have found increased prevalence of migraines in people with certain conditions, including epilepsy, insulin resistance, obesity, fibromyalgia and certain cardiovascular conditions (see Ongoing research).