Although much about headaches still isnt understood, some researchers think migraines may be caused by functional changes in the trigeminal nerve system, a major pain pathway in your nervous system, and by imbalances in brain chemicals, including serotonin, which plays a regulatory role for pain messages going through this pathway. During a headache, serotonin levels drop. Researchers believe this causes the trigeminal nerve to release substances called neuropeptides, which travel to your brains outer covering (meninges). There they cause blood vessels to become dilated and inflamed. The result is headache pain. Migraine triggers whatever the exact mechanism of headaches, a number of things may trigger them. Common migraine triggers include: Hormonal changes. Although the exact relationship between hormones and headaches isnt clear, fluctuations in estrogen seem to trigger headaches in many women with known migraines. Women with a history of migraines often report headaches immediately before or during their periods, and this corresponds to a major drop in estrogen. Others have an increased tendency to develop migraines during pregnancy or menopause. Hormonal medications, such as contraceptives and hormone replacement therapy, also may worsen migraines. Foods. Certain foods appear to trigger headaches in some people. Common offenders include alcohol, especially beer and red wine; aged cheeses; chocolate; fermented, pickled or marinated foods; aspartame; overuse of caffeine; monosodium glutamate — a key ingredient in some Asian foods; certain seasonings; and many canned and processed foods. Skipping meals or fasting also can trigger migraines. Stress. A hard week at work followed by relaxation may lead to a weekend migraine. Stress at work or home also can instigate migraines. Sensory stimuli. Bright lights and sun glare can produce head pain. So can unusual smells — including pleasant scents, such as perfume and flowers, and unpleasant odors, such as paint thinner and secondhand smoke. Changes in wake-sleep pattern. Either missing sleep or getting too much sleep may serve as a trigger for migraine attacks in some individuals. Physical factors. Intense physical exertion, including sexual activity, may provoke migraines. Changes in the environment. A change of weather, season, altitude level, barometric pressure or time zone can prompt a migraine. Medications. Certain medications can aggravate migraines.