Migraines happen because your brain is more reactive than average to certain internal and external changes. Rather than a single cause, migraines result from a combination of genetic wiring, nervous system sensitivity, hormonal shifts, and environmental triggers that lower your threshold for an attack. Understanding which factors apply to you is the first step toward getting fewer of them.
Your Brain Processes Signals Differently
The core issue in migraine isn’t damage or disease. It’s a nervous system that responds more intensely to stimulation. People who get migraines have heightened activity in neurotransmitter systems, particularly the ones that control excitation and inhibition in the brain. Research using high-powered brain imaging has shown that levels of the brain’s main inhibitory chemical shift upward as a migraine attack approaches, likely as the brain tries (and fails) to compensate for rising excitability. This imbalance between excitatory and calming signals is what sets the stage for an attack.
Think of it as a lower threshold. Where someone without migraines can absorb a night of poor sleep or a skipped meal without consequence, your brain treats those same disruptions as alarm signals. Once the threshold is crossed, a chain reaction begins in the trigeminal nerve, the largest nerve in your head, responsible for sensation across your face, jaw, and the protective membranes around your brain. Activation of this nerve releases a signaling molecule called CGRP, which triggers inflammation around blood vessels in the brain, sensitizes pain pathways, and ultimately produces the throbbing, debilitating headache you recognize as a migraine.
CGRP is central enough to migraine biology that it’s become a treatment target. Levels of CGRP rise during attacks and drop after successful treatment. Injecting it into migraine-prone people reliably triggers migraine-like headaches, while blocking it with newer medications prevents attacks. If you’ve heard of monthly migraine injections, this is the mechanism they’re built around.
Genetics Load the Gun
Migraines run in families. If one of your parents gets migraines, your risk is substantially higher, and if both do, the odds climb further. Genome-wide studies have identified specific regions of DNA linked to migraine susceptibility, including areas involved in CGRP production. You didn’t choose to have a reactive nervous system. You inherited the wiring for one.
This genetic component also helps explain why migraines often appear in adolescence or early adulthood and why they can shift in frequency and severity over a lifetime. Your baseline susceptibility is set by your genes, but what pushes you over the threshold on any given day depends on everything else going on in your body and environment.
Hormonal Shifts Are a Major Driver
If you menstruate, hormones are likely playing a significant role. Estrogen directly affects headache-related chemicals in the brain, and drops in estrogen are a well-established migraine trigger. The classic pattern is a migraine arriving in the day or two before your period, when estrogen falls sharply. Steady estrogen levels tend to improve migraines, while sudden changes in either direction make them worse.
This is why migraines often improve dramatically during pregnancy, when estrogen rises quickly and stays elevated for months. It’s also why they frequently return after delivery, when estrogen plummets. Women going through perimenopause, when estrogen levels become erratic, often experience their worst migraine years before attacks taper off after menopause. Hormonal contraceptives can go either way: stabilizing estrogen may help some people, while the hormone-free week in combination pills can trigger attacks in others.
What Triggers Actually Do
Triggers don’t cause migraines on their own. They push an already-sensitive brain past its threshold. That’s why a glass of red wine might give you a migraine one week and not the next. Your threshold fluctuates based on sleep, stress, hydration, hormones, and other factors stacking on top of each other.
Common triggers include:
- Sleep disruption: Both too little and too much sleep can trigger attacks. A large analysis of nearly 39 million people found that irregular night-shift work increased migraine odds by 61% compared to regular schedules. Your brain’s internal clock regulates pain sensitivity, hormone release, and neurotransmitter cycles, so disrupting it has outsized effects on migraine.
- Weather changes: Barometric pressure swings are a real trigger, not just anecdotal. Days when pressure fluctuates by more than 5 hectopascals (a moderate weather shift) are associated with increased migraine occurrence. Seasons with the largest pressure changes show roughly 29% higher migraine risk after adjusting for other factors.
- Stress and stress letdown: Ongoing stress keeps your nervous system on high alert, but the period right after stress resolves, like the first day of a vacation, is often when the attack arrives.
- Skipped meals and dehydration: These lower your threshold quickly. The brain is metabolically demanding, and even mild energy or fluid deficits register as threats in a migraine-prone system.
- Sensory overload: Bright lights, strong smells, and loud environments can all push you past your limit, particularly if other triggers are already in play.
Why Some Attacks Include Aura
About a quarter to a third of people with migraines experience aura, typically visual disturbances like zigzag lines, blind spots, or shimmering patches that develop over 5 to 20 minutes before the headache arrives. Some people get tingling in their hands or face, or temporary difficulty finding words.
Aura is caused by a slow wave of electrical disruption that rolls across the surface of the brain, called cortical spreading depression. Neurons fire intensely and then go quiet, suppressing normal brain activity in their wake. For decades this was theoretical, but researchers recently captured the first direct recording of it during a migraine, using electrodes already placed in a patient’s brain for epilepsy monitoring. Brainwave activity on one side went flat and stayed suppressed for hours. This wave of disruption is what produces the visual and sensory symptoms, and it also activates the trigeminal pain pathways that produce the headache that follows.
Episodic vs. Chronic Migraine
Most people with migraines have the episodic form, meaning attacks come and go with stretches of normal days in between. A typical migraine lasts 4 to 72 hours untreated and has at least two of these features: pain on one side of the head, a pulsating quality, moderate to severe intensity, or worsening with routine activity like walking or climbing stairs. During the attack, you’ll also have nausea, vomiting, or sensitivity to light and sound.
Chronic migraine is defined as headache on 15 or more days per month for more than three months, with at least 8 of those days meeting migraine criteria. This isn’t just “more migraines.” Chronic migraine involves changes in how the brain processes pain, with the nervous system becoming increasingly sensitized over time. One of the biggest risk factors for developing chronic migraine is overusing acute pain medications (including over-the-counter options), which paradoxically makes headaches more frequent.
Why Your Migraines May Be Getting Worse
If your migraines have increased in frequency or intensity, several patterns are worth examining. Medication overuse, defined as using acute treatments on 10 or more days per month, is one of the most common and reversible causes of worsening migraines. Poor sleep consistency, rising stress, or a new hormonal shift (starting or stopping contraception, entering perimenopause) can also change the pattern. Weight gain, increased caffeine intake, and untreated anxiety or depression are all associated with migraine progression.
The encouraging flip side is that many of these factors are modifiable. Keeping a consistent sleep schedule matters more than total hours slept. Eating at regular intervals, staying hydrated, and managing stress don’t eliminate migraines, but they raise the threshold at which an attack gets triggered. For people whose migraines remain frequent despite lifestyle changes, preventive treatments targeting the CGRP pathway or other mechanisms can reduce attack frequency by half or more.