Migraines happen because of a chain reaction in an overly excitable nervous system, where a trigger sets off electrical and chemical changes in the brain that produce intense pain, nausea, and sensory disturbances. About 1.2 billion people worldwide live with migraines, and the condition is rooted in a combination of genetics, hormones, and environmental sensitivity rather than any single cause.
What Happens Inside the Brain During a Migraine
A migraine is not just a bad headache. It’s a neurological event that unfolds in stages, driven by abnormal nerve signaling and inflammation. The process centers on the trigeminal nerve, a branching network that connects sensors in your facial skin, muscles, teeth, and mucous membranes to your brainstem. When something activates this system, the nerve sends electrical signals to the brainstem, which then relay to the outer covering of the brain called the dura.
Once activated, nerve endings release chemicals that cause blood vessels in the brain to swell, contract, and become leaky. The immune system kicks in, and the result is inflammation inside and around the brain. One of the key chemicals involved is a signaling molecule called CGRP, which rises in the bloodstream during an attack and falls again as the pain fades. CGRP doesn’t just drive head pain. It also affects the gut, influencing nausea, vomiting, and the digestive slowdown that many people experience during a migraine.
For people who get aura (visual disturbances like flickering lights or blind spots), there’s an additional process at work. A wave of intense electrical activity sweeps across the surface of the brain, followed by a period where neurons essentially go silent. This wave disrupts normal ion balance in brain cells, flooding them with calcium and sodium while potassium builds up outside. As inflammatory molecules from this event reach the brain’s outer lining, the aura symptoms appear, and the painful headache typically follows.
Genetics Set the Stage
If your parents get migraines, your chances of getting them rise significantly. Heritability is estimated at 38% for men and 48% for women, meaning that familial factors contribute to roughly half of all migraine cases. The rest comes down to environment, hormones, and individual triggers.
Researchers have identified specific gene mutations in rare, severe forms of migraine that run in families. These mutations affect ion channels and sodium-potassium pumps, the cellular machinery responsible for controlling electrical signaling in the brain. While most people with migraines don’t carry these rare mutations, the discovery confirmed that migraines are fundamentally a disorder of brain excitability. People who get migraines have nervous systems that are more reactive to stimulation, and that reactivity is partially inherited.
Why Women Get Migraines Far More Often
Women between the ages of 30 and 44 carry a disproportionately high burden of migraines globally. The reason is largely hormonal. Estrogen fluctuations, particularly the drop that happens just before menstruation, appear to destabilize serotonin levels in the brain. Serotonin is a chemical messenger that helps regulate pain perception, mood, and blood vessel tone. During the luteal phase of the menstrual cycle, when migraine attacks spike in frequency, serotonin levels decline.
Research published in JAMA found that in the absence of estrogen, women with a history of severe, prolonged migraines had significantly impaired brain chemical responses. Those responses were restored when they received both a serotonin-targeting treatment and supplemental estrogen. This helps explain why migraines often worsen around periods, improve during pregnancy (when estrogen is high and stable), and sometimes resolve after menopause.
Common Triggers and Why They Work
The migraine-prone brain overreacts to changes that a typical brain would shrug off. Triggers don’t cause migraines on their own. They activate the chain reaction in someone whose nervous system is already primed for it. Common triggers include:
- Weather changes: Drops in barometric pressure, like those before a storm, affect the air-filled sinus and nasal cavities. This forces fluid into surrounding tissues and may alter the pressure on the brain itself, disrupting the way the brain processes pain signals.
- Sleep disruption: Both too little and too much sleep can trigger an attack, likely because sleep regulates the same serotonin and electrical signaling pathways involved in migraines.
- Stress and stress letdown: The brain’s stress-response system overlaps heavily with migraine pathways. Many people find that attacks hit not during peak stress, but in the hours or days after the stress resolves.
- Sensory overload: Bright lights, strong smells, and loud noise can push an already excitable nervous system past its threshold.
- Skipped meals and dehydration: Blood sugar drops and fluid imbalances affect brain energy metabolism, and the migraine brain is particularly sensitive to these shifts.
For most people, a single trigger isn’t enough. Attacks tend to happen when multiple factors stack, such as poor sleep combined with a weather shift and a skipped meal. This is why the same trigger can cause a migraine one week but not the next.
The Four Phases of an Attack
A migraine isn’t just the headache. It typically unfolds across four distinct phases, though not everyone experiences all of them.
The prodrome phase starts one to two days before the pain. Symptoms include food cravings, neck stiffness, mood shifts (ranging from depression to unusual euphoria), increased thirst and urination, frequent yawning, and constipation. These early warning signs reflect changes already happening in the brainstem and hypothalamus. Many people learn to recognize their prodrome and use it to prepare or start early treatment.
The aura phase, which affects roughly a quarter of people with migraines, typically lasts 20 to 60 minutes. It’s caused by that wave of electrical disruption spreading across the brain’s surface. Visual effects like zigzag lines, sparkles, or temporary blind spots are most common, but some people experience tingling, numbness, or difficulty speaking.
The headache phase brings throbbing or pulsing pain, usually on one side, along with nausea, vomiting, and extreme sensitivity to light, sound, or smell. This can last anywhere from four hours to three days. The pain comes from the inflammation and blood vessel changes triggered by the trigeminal nerve system.
The postdrome phase, sometimes called a “migraine hangover,” can linger for a day or two after the pain resolves. People describe feeling drained, confused, or washed out. Sudden head movement may briefly bring back a flash of pain.
How Migraines Affect the Brain Over Time
One concern people have is whether migraines cause lasting brain damage. Research from the ARIC MRI study, published in Neurology, found that people with migraine without aura had an 87% greater chance of having areas of white matter changes on brain scans compared to people without headaches. These changes showed up as small bright spots on MRI, representing areas where brain tissue structure is slightly altered.
The reassuring finding, though, is that migraines did not appear to cause these changes to worsen faster over time. People with migraines did not show significantly more progression of white matter changes over the study period compared to those without migraines. Interestingly, migraines with aura did not show the same association with white matter changes that migraines without aura did, which suggests the relationship is more complex than simple wear and tear from repeated attacks.
Why Some People Get Migraines and Others Don’t
The short answer is threshold. Everyone’s brain has a point at which it can be pushed into a migraine-like state, but in people with migraines, that threshold is much lower. Genetics account for roughly half of this sensitivity. Hormones lower the threshold further, which is why women are affected so much more often. And then daily life provides the triggers that push someone over the edge on any given day.
This threshold model explains why migraines change over a lifetime. They often begin during puberty when hormones shift, peak in the 30s and 40s when life stressors and hormonal cycling are at their most intense, and frequently improve with age. It also explains why lifestyle consistency, keeping regular sleep, meals, hydration, and stress levels, is one of the most effective ways to manage the condition. You can’t change your genetics or rewire your trigeminal nerve, but you can keep the daily load of triggers below your threshold.