Migraines are caused by a combination of genetic sensitivity, nervous system overreactivity, and a wide range of triggers that vary from person to person. Unlike a tension headache, a migraine involves a specific chain reaction in the brain: nerve cells become overly excitable, release inflammatory chemicals, and activate pain pathways that produce throbbing head pain, nausea, and sensitivity to light or sound. Understanding both the underlying biology and the common triggers can help you identify patterns and reduce attack frequency.
How a Migraine Starts in the Brain
The pain of a migraine originates in a network called the trigeminovascular system. Nerve fibers from the trigeminal nerve, the largest sensory nerve in the head, wrap around blood vessels in the brain and its protective membranes. When these fibers become activated, they release signaling molecules that cause blood vessels to widen and surrounding tissue to become inflamed. That inflammation irritates more nerve endings, amplifying the pain signal.
One of the key molecules involved is a protein called CGRP (calcitonin gene-related peptide). During a migraine attack, blood levels of CGRP rise and fall in step with headache intensity. CGRP drives blood vessel dilation and promotes the inflammatory cascade that sustains the attack. This discovery has been so central to migraine science that an entire class of preventive medications now works by blocking CGRP activity.
Serotonin, a brain chemical involved in nerve cell communication, also plays a role. Waves of excitable brain cell activity trigger serotonin release, which initially narrows blood vessels. When serotonin levels then drop, blood vessels rebound and dilate, contributing to the pulsing pain that characterizes migraines. These chemical fluctuations help explain why migraines unfold in phases rather than hitting all at once.
What Causes Migraine Aura
About 25 to 30 percent of people with migraines experience aura, typically visual disturbances like shimmering lines, blind spots, or zigzag patterns that develop over several minutes before the headache begins. The cause is a phenomenon called cortical spreading depression: a slow wave of intense nerve cell firing followed by a prolonged period of suppressed activity that moves across the brain’s surface.
Functional MRI studies have captured this wave in real time. It starts with a surge of blood flow in the visual processing area at the back of the brain, then creeps across the cortex at roughly 3.5 millimeters per minute. As it passes, blood flow drops below normal levels. The visual symptoms you see during aura directly correspond to which part of the visual cortex the wave is passing through. Not everyone who has cortical spreading depression experiences visible aura symptoms, which is why some migraines cause the same brain disruption without the warning signs.
Hormonal Shifts and Estrogen
Hormones are one of the most powerful migraine triggers, which is a major reason women experience migraines about three times more often than men. Estrogen plays a central role. Steady estrogen levels tend to protect against migraines, but sudden drops can set off an attack.
The most common hormonal pattern is the menstrual migraine. Estrogen peaks in the middle of the menstrual cycle, then drops sharply in the days just before a period begins. That decline is enough to trigger a migraine in many susceptible people. These menstrual migraines tend to be longer, more severe, and harder to treat than migraines at other times of the month. The same principle applies during other hormonal transitions: the postpartum period, perimenopause, and the hormone-free interval in certain birth control pills can all create the kind of estrogen withdrawal that lowers the migraine threshold.
Food and Drink Triggers
Certain foods trigger migraines not because of allergies, but because of naturally occurring chemicals that affect blood vessels and nerve signaling. Tyramine is one of the most well-established culprits. It forms when the amino acid tyrosine breaks down, which happens during aging, fermenting, and long storage. Aged cheeses, cured meats, fermented soy products, and some wines are all high in tyramine. The compound causes blood vessel changes that can initiate the migraine cascade in sensitive people.
Other dietary triggers include nitrates (found in processed meats like hot dogs and deli ham), alcohol (especially red wine and beer), artificial sweeteners, and caffeine, though caffeine’s relationship with migraines is complex. Small amounts can actually relieve a migraine, while excessive intake or sudden caffeine withdrawal frequently triggers one. Individual sensitivity varies widely. A food that reliably triggers migraines in one person may be completely harmless to another, which is why keeping a food diary is more useful than following a generic avoidance list.
Sleep and Circadian Disruption
People with migraines have brains that are unusually sensitive to changes in routine, and sleep is one of the most potent regulators. Both too little sleep and too much sleep can trigger an attack. The issue isn’t just total hours but consistency. Sleeping in on weekends, jet lag, shift work, and even the one-hour clock change during daylight saving time are all documented migraine triggers. Research from UC Davis Health found that even a minor change in sleep pattern can be enough to trigger a migraine in someone with a sensitive brain.
This sensitivity likely relates to the hypothalamus, a brain region that controls the body’s internal clock and also has direct connections to the pain pathways involved in migraines. When your sleep-wake cycle is disrupted, the hypothalamus sends altered signals through those same pathways, effectively lowering the threshold at which a migraine can be triggered.
Stress and the Letdown Effect
Stress is the single most commonly reported migraine trigger, cited by roughly 70 percent of people with the condition. But the relationship is counterintuitive. Many people don’t get migraines during the stressful event itself. Instead, the attack hits during the “letdown” period afterward: the weekend after a brutal work week, the first day of vacation, or the hours after a major deadline passes. During stress, cortisol and other hormones may temporarily suppress the migraine process. When stress hormones drop, the brain’s defenses relax and a migraine breaks through.
Chronic stress also makes migraines progressively worse over time. Repeated activation of the body’s stress response sensitizes pain pathways, meaning it takes a smaller and smaller trigger to set off an attack. This is one mechanism by which episodic migraines (fewer than 15 days per month) can gradually transform into chronic migraines.
Weather and Environmental Triggers
Changes in barometric pressure, bright sunlight, high humidity, and extreme heat are all established environmental triggers. Barometric pressure shifts, the kind that happen before a storm front, are among the most commonly reported. The mechanism likely involves pressure changes affecting serotonin balance in the brain. Some people can reliably predict weather changes based on the onset of their migraine symptoms.
Strong sensory stimuli also play a role. Flickering or fluorescent lights, strong perfumes, cigarette smoke, and loud or repetitive sounds can all push a sensitive nervous system past its threshold. These triggers tend to be more potent when you’re already primed by another factor like poor sleep or skipped meals, which is why migraines often result from a combination of triggers rather than a single cause.
Genetic Predisposition
Migraine has a strong hereditary component. If one of your parents has migraines, you have roughly a 50 percent chance of developing them. If both parents are affected, that risk rises to about 75 percent. What you inherit isn’t a single “migraine gene” but a collection of genetic variations that make your brain more excitable and more reactive to triggers. Researchers have identified over 100 gene regions associated with migraine risk, many of which affect ion channels (the gates that control electrical signaling in nerve cells), blood vessel function, and pain processing.
This genetic excitability explains why migraine is fundamentally a threshold disorder. Everyone has some theoretical threshold at which their brain could produce a migraine. People with a strong genetic predisposition simply have a lower threshold, meaning fewer or milder triggers are needed to push them over the edge. It also explains why triggers are so variable from person to person: different genetic profiles create different vulnerabilities.
Skipped Meals and Dehydration
Fasting and irregular meals are reliable migraine triggers for many people. Going more than a few hours without eating causes blood sugar to drop, which in turn affects serotonin levels and blood vessel tone in the brain. Dehydration has a similar effect, reducing blood volume and potentially triggering compensatory changes in brain blood flow. For people prone to migraines, eating at consistent intervals and staying well hydrated are among the simplest and most effective preventive strategies. Even mild dehydration, the kind you might not notice as thirst, can be enough to lower the migraine threshold on a day when other triggers are also present.