The exact cause of migraine is not fully understood. For a long time, the generally accepted theory was that migraine and its symptoms were caused by problems in the blood vessels of the head. Recent research, however, has shown that, while blood vessel constriction can result in pain, the cause of migraine, itself, is likely rooted in a disorder of the central nervous system.
The chain of physical and chemical events in and around the brain that leads to migraine headaches is still unclear. What is known is that something activates a cascade of biochemical reactions that may trigger an inflammatory response and overexcitement of the trigeminal nerve, a major pain pathway which controls sensation in the face and head. This overexcitement spreads to other nerves in the meninges—the protective membrane covering the brain—and leads to pain and other migraine symptoms.
Research to understand the details of this process is ongoing, but the following are suspected as important factors in causing migraine headaches:
- low levels of serotonin—a neurotransmitter that controls mood, sleep, and appetite—that cause painful blood vessel constriction
- dietary deficiency in magnesium, a mineral that is important for nerve function
- neuropeptides—small protein-like molecules—that trigger inflammation and cause pain receptors to activate
- abnormalities in the way cells transport calcium ions, which are used in transmitting nerve signals
- the release of nitric oxide—a chemical that signals blood vessels to dilate—by overactive neurons
- hormonal fluctuations, especially of estrogen in women
- inflammation of the maxillary nerve, a branch of the trigeminal nerve that runs behind the cheekbone and controls sensation in the mouth and nose
Although the specifics of migraine neurobiology are unknown, there are many factors known to make migraine headaches more likely to occur. Each patient's triggers may be different, but most fall into the following categories:
- Changes in emotional stress levels. Increased stress at home or at work can trigger a headache, as can a reduction in stress, such as finishing an important project or going on vacation.
- Certain foods and chemicals, including chocolate, alcohol, nuts, monosodium glutamate (MSG), aged cheeses, processed meats such as hot dogs or cold cuts, high levels of caffeine, and aspartame (the artificial sweetener in Equal and NutraSweet)
- Hunger or dehydration, especially when caused by a skipped meal
- Changing weather conditions, including barometric pressure, humidity, and temperature
- Changes to sleep patterns, whether getting more or less sleep than normal
- Bright lights, such as direct sunlight without sunglasses or light emitted from a movie screen
- Loud sounds, such as construction equipment or a concert
- Strong odors, such as excessive perfume, cologne, or air freshener
- Intense physical activity including exercise, lifting heavy objects, or sexual activity
- Hormonal changes in women, whether related to menstrual period, pregnancy, birth control pills, or hormone replacement therapy for menopause