Migraine headaches are caused by abnormal activity in the brain’s pain-signaling network, not by blood vessel problems alone as once believed. The process involves a major nerve system in the head firing inappropriately, releasing inflammatory chemicals that create intense, throbbing pain. But the full picture includes genetics, hormones, brain structure, and a long list of environmental triggers that can set the whole cascade in motion.
The Pain Pathway in Your Brain
The core mechanism behind migraine pain centers on what scientists call the trigeminovascular system: a network connecting the trigeminal nerve (the largest nerve in your head) to the blood vessels lining your brain. During a migraine, this nerve becomes activated and releases powerful inflammatory signaling molecules from its endings in the membranes surrounding the brain. These molecules cause blood vessels to dilate and surrounding tissue to become inflamed and hypersensitive.
One of the most important of these signaling molecules is called CGRP. It’s so central to migraine pain that an entire class of newer migraine medications works by blocking it. When CGRP floods the space around your brain’s blood vessels, it triggers swelling, sensitizes nearby nerve fibers, and amplifies pain signals traveling back to the brainstem. This creates a feedback loop: the nerve fires, releases inflammatory chemicals, those chemicals make the nerve even more excitable, and the pain intensifies.
What makes this system fire in the first place appears to start deeper in the brain. Longitudinal brain imaging studies have found that specific brainstem regions, including the spinal trigeminal nucleus and an area called the periaqueductal gray (PAG), show measurable changes in activity within 24 hours before a migraine begins. These shifts happen before any pain starts, supporting the idea that migraine originates as a brain event rather than a vascular one. The brainstem may either initiate the attack directly or lower the threshold so that an outside trigger can set it off.
What Happens During Aura
About one in four people with migraines experience aura, typically visual disturbances like shimmering zigzag lines, blind spots, or flashing lights that appear 20 to 60 minutes before the headache. These are caused by a slow-moving electrical wave that rolls across the surface of the brain, called cortical spreading depression. It starts with a burst of intense nerve cell activity (which produces the visual sparkles or scintillations), followed immediately by a prolonged shutdown of neural activity (which creates blind spots or scotomas).
Functional MRI studies have captured this wave in real time. It moves across the visual cortex at roughly 3.5 millimeters per minute, progressing from the back of the brain toward the front. This matches perfectly with what patients report: visual disturbances typically start in the center of their visual field and slowly expand outward. The initial wave causes a 5% increase in blood flow signals, corresponding to the bright flickering people see. That’s followed by a roughly 5% decrease, corresponding to the temporary blind spot that trails behind the sparkles. This wave is also thought to activate the trigeminal pain pathway, linking the aura directly to the headache that follows.
Hormones and Estrogen Drops
Migraines are roughly two to three times more common in women than men, and hormones are a major reason why. Estrogen plays a direct role in regulating pain-related chemicals in the brain. When estrogen levels are steady or rising, migraines tend to improve. When estrogen drops sharply, migraine risk spikes.
This explains several patterns women commonly notice. Menstrual migraines cluster in the days just before or during a period, exactly when estrogen falls most steeply. Pregnancy often brings relief, especially after the first trimester, because estrogen rises rapidly and stays elevated. Perimenopause, when hormone levels fluctuate unpredictably, is frequently the worst period for migraine frequency. And some women find that hormonal birth control either helps or worsens their migraines depending on whether the formulation stabilizes or disrupts their estrogen levels.
Genetics Set the Stage
If one of your parents has migraines, you have roughly a 50% chance of developing them. If both parents do, that risk climbs to about 75%. Migraine runs in families because the genes involved affect how excitable your brain’s nerve cells are, how efficiently your brain clears inflammatory chemicals, and how sensitive your pain-processing pathways are to stimulation.
No single “migraine gene” has been identified. Instead, dozens of genetic variants each contribute a small amount of vulnerability. Most of these variants affect ion channels (the tiny gates that control electrical signaling in nerve cells) or influence serotonin and other neurotransmitter systems. The net effect is a nervous system that’s more reactive to changes in environment, sleep, stress, and other inputs. This is why migraine is often described as a threshold disorder: your brain has a lower tolerance for disruption, and various triggers can push you past that threshold into an attack.
Common Triggers and Why They Matter
Triggers don’t cause migraine in the way a virus causes a cold. They act more like the last straw for a brain that’s already predisposed. A trigger that sets off an attack one day might have no effect another day, depending on how many other factors are stacking up at the same time. That said, certain triggers are consistently reported across large populations of migraine patients.
- Sleep disruption: Both too little and too much sleep can provoke attacks. Research comparing migraine patients with poor versus good sleep quality found that poor sleepers averaged about 17 headache days per month compared to roughly 12 for good sleepers. The correlation between sleep quality scores and headache frequency was statistically significant, and poor sleep was also linked to a higher risk of episodic migraines becoming chronic.
- Food triggers: Fermented or pickled foods, aged cheeses, and processed or cured meats (like hot dogs and deli meats) are among the most commonly reported dietary triggers. Preservatives found in many packaged foods can also be problematic. Alcohol, particularly red wine, and caffeine withdrawal are frequent culprits as well.
- Sensory overload: Bright or flickering lights, loud noises, and strong smells can all initiate an attack. These same stimuli also worsen symptoms once a migraine is underway, which is why most people instinctively retreat to a dark, quiet room.
- Weather changes: Sudden shifts in temperature, drops in barometric pressure, and seasonal transitions are reliable triggers for many people. You can’t control the weather, but tracking patterns can help you prepare.
- Stress and its aftermath: Stress itself is a well-known trigger, but many people find that migraines actually hit hardest during the “letdown” period after stress resolves. Weekend migraines or vacation headaches often follow this pattern.
How Triggers Stack Up Together
One of the most useful concepts in understanding migraine triggers is the idea of a cumulative threshold. On any given day, your brain can tolerate a certain amount of disruption before tipping into an attack. Poor sleep alone might not do it. Neither might skipping a meal. But poor sleep combined with a skipped meal, a glass of wine, and a stressful meeting might push you over the edge.
This is why keeping a headache diary can be genuinely helpful. When you track your attacks alongside sleep, food, stress, menstrual cycle, and weather, patterns often emerge that aren’t obvious in the moment. You may discover that your triggers are predictable combinations rather than single culprits. That knowledge lets you manage the factors you can control (sleep regularity, meal timing, hydration) even when you can’t control others (weather, work stress).
The Prodrome Phase: Early Warning Signs
Hours or even a day before the headache begins, many people experience subtle changes: food cravings, neck stiffness, frequent yawning, irritability, or difficulty concentrating. This prodrome phase is now understood to reflect the early brain changes that precede the full attack. The brainstem regions that show altered activity 24 hours before a migraine line up with these symptoms, since they regulate alertness, mood, appetite, and muscle tone.
Prodrome symptoms are sometimes mistaken for triggers. A common example: someone craves chocolate during the prodrome, eats it, then gets a migraine and blames the chocolate. In reality, the craving was an early symptom of the attack that was already underway. Understanding the prodrome helps you recognize when a migraine is building so you can respond early, whether that means taking medication, adjusting your schedule, or prioritizing sleep.