Migraine is a debilitating condition, affecting between 12 million and 24 million Americans. Unlike tension headaches, migraines can last from several hours to several days and in some cases, even months or years. Some of the symptoms that accompany migraines are:

• Loss of vision
• Vomiting
• Tremors
• Numbness in parts of the body

Migraine pain usually occurs on one side of the head, although it can appear on both sides. Many people's migraines switch sides.

Although doctors aren't completely sure how migraines work, they think in most cases that the following sequence of events leads to a migraine:

1. The triggering event occurs - - for example, you missed breakfast and now lunch is late.

2. Pain-sensing nociceptors in the brainstem sense this change in routine and release neuropeptides.

3. The neuropeptides attack nearby pain-sensing cells, making them more pain sensitive and releasing more neuropeptides.

4. Some of the neuropeptides work on muscles around blood vessels near the brain's surface. The muscles relax, the blood vessels dilate, and blood flow increases.

5. Some neuropeptides cause the cranial vessels to leak, swelling the surrounding tissue.

A trigger is the condition or event that initiates this chain of events. Some common triggers are environmental, such as weather, bright lights and loud noises. Some we can control more, such as waking up too early or too late and eating or drinking certain foods. For some people, alcohol, caffeine or hard cheeses trigger attacks. Even missing regular caffeine can bring on a migraine. Hormonal changes may explain many migraines, especially in women. Migraines love variety in behavior. Even changing your routine a little can trigger a migraine.

Doctors continue to study what causes migraine pain and why some people are so susceptible to these triggers. New evidence suggests that factors such as chemical release and increased pain sensitivity occur simultaneously, and cause most migraine pain. Doctors have recently classified migraine as a neurobiological condition, originating in the brain. Researchers also know that genetics can play a role in migraines. This means that if one of your parents has migraines, you have a 50 percent chance of developing them. If both of your parents have migraines, your chances rise to about 70 percent.