What Causes Migraines? What Happens in Your Brain

By Laurine NicolettiOctober 15, 202610 min

You get a migraine, and you wonder: why me, and why now? Maybe it hit after a stressful week, or on a perfectly ordinary Tuesday with no obvious reason. People often expect a single clear answer to what causes migraines, and the honest answer is that it is not one thing.

Migraine is a condition of the nervous system. Your brain reacts more strongly than average to certain changes, and that reaction sets off a chain of signals that ends in pain and other symptoms. This article walks through that chain in plain language. If you want the wider picture first, our guide All about migraine is a good starting point.

In short

Migraine is thought to come from abnormal brain activity that temporarily affects nerve signals, chemicals and blood vessels, according to Mayo Clinic.
The trigeminal nerve, a major pain pathway in the head, and a chemical messenger called CGRP play a central role in how the pain develops.
Genes make you more likely to have migraine, but no single gene decides it, and many people with migraine have a close relative with it.
Triggers such as stress or poor sleep are not the root cause: they are things that can tip a sensitive brain into an attack.

Why does the migraine brain react more strongly?

A migraine brain is best described as more sensitive and more excitable than average, not damaged. The NHS says the exact cause is unknown, but migraines are thought to result from abnormal brain activity temporarily affecting nerve signals, chemicals and blood vessels in the brain.

Think of it like a smoke alarm set a little too sensitive. It works, and it is protecting you, but it goes off at toast, not only at fire. Scientists describe migraine as a disorder of the nervous system with a prominent genetic basis, and studies suggest that brainstem and cortical excitability change across the migraine cycle, rather than staying fixed.

This is also why migraine is more than a headache. The same sensitive system handles light, sound, smell and nausea, which explains why those symptoms often come along. For the difference between a migraine and an ordinary headache, see Migraine vs headache.

Where does an attack start?

Many researchers think an attack can begin deep in the brain, before any pain appears. Brain imaging studies of the premonitory phase (the early warning stage) point to areas such as the hypothalamus, thalamus and brainstem, as a review of the evidence describes.

The hypothalamus helps regulate sleep, appetite and mood. That fits with the early signs many people notice: yawning, tiredness, food cravings, a low mood or a stiff neck. The American Migraine Foundation notes that about 75% of people with migraine experience this early phase, often without recognising it as the start of an attack.

How do the trigeminal nerve and CGRP create the pain?

The trigeminal nerve and a chemical called CGRP are two of the main players in migraine pain. Mayo Clinic explains that changes in the brainstem and its interactions with the trigeminal nerve, a major pain pathway, might be involved.

The trigeminal nerve carries sensation from your face, eyes and the coverings of your brain. When it is activated, it releases chemical messengers, including calcitonin gene-related peptide, known as CGRP. The NHS notes that changes in brain chemicals including serotonin and CGRP occur during an attack.

In simple terms, the sequence looks like this:

A sensitive brain network becomes active.
The trigeminal nerve is activated and releases CGRP around blood vessels and tissues that cover the brain.
Pain signals travel back into the brain and are amplified, which is why the pain throbs and why light, sound and movement can make it worse.

CGRP is also why newer preventive treatments exist. Antibodies that target CGRP are too large to cross easily into the brain, which suggests the key action happens outside it, along the nerve and its blood vessels. We explain these medicines in CGRP inhibitors for migraine prevention. Whether one is right for you is a conversation for your doctor.

If any of the terms here feel new, our migraine glossary explains them one by one.

What happens in the brain during an aura?

During an aura, a slow wave of electrical activity is thought to move across the surface of the brain, then quiet it down. This is called cortical spreading depression, and Cleveland Clinic describes it as a wave that interrupts normal functioning and causes the symptoms of an aura.

Where the wave travels decides what you feel. If it crosses the area that processes vision, you may see zigzags, sparks or blind spots. If it moves through areas for sensation or speech, you may feel tingling or have trouble finding words.

Some details are still unclear. Cleveland Clinic states that the exact reason this wave starts is unknown. Researchers have also looked at how it may connect to the trigeminal system: a laboratory study found that spreading depolarization led to CGRP production in trigeminal neurons. That is early science, mostly in animals, not a proven chain for every person.

You can read more about the warning signs in migraine with aura and migraine without aura.

Is migraine hereditary?

Migraine runs in families, but it is a predisposition, not a certainty. The American Migraine Foundation describes migraine as influenced by many genes, with no single gene that dictates whether a person develops it.

Family studies suggest that heritability is somewhere between 35% and 60%. In other words, genes explain a large share of who is more likely to get migraine, and environment and life circumstances explain the rest. Cleveland Clinic adds that up to 80% of people with migraine have a close biological relative who also has it.

Rare forms are different. Some types, like familial hemiplegic migraine, are linked to changes in specific genes that affect how nerve cells handle electrical charge, such as CACNA1A, ATP1A2 and SCN1A, as described by The Migraine Trust. Most people have the common, many-gene form.

For a deeper look, read Is migraine hereditary?.

Why are women affected more often?

Hormones appear to be part of the story. The American Migraine Foundation reports that migraine is about three times more common in women than men, and that the gap opens after puberty: in childhood, boys and girls are affected at similar rates.

Estrogen is the hormone most often discussed. Mayo Clinic says fluctuations in estrogen seem to trigger headaches in many women, before or during periods, in pregnancy and around menopause. This is not a cause on its own. It is another reason a sensitive brain may react at certain times. See menstrual migraine for more.

Triggers are not causes

A trigger is something that can set off an attack in a sensitive brain, while the cause is the sensitivity itself. The NHS explains that an attack occurs when triggers activate these chemical and electrical pathways, and it lists hormonal, emotional, physical, dietary, environmental and medicinal factors.

Common triggers named by Mayo Clinic include:

hormonal changes
stress
too much caffeine, and alcohol (especially wine)
bright or flashing lights, loud sounds and strong smells
too little or too much sleep
weather changes
skipped meals and some foods

Triggers are also tricky to pin down. The American Migraine Foundation points out that some "triggers" may actually be early signs that an attack has already begun. If you crave chocolate because the attack is starting, the chocolate gets the blame, even though the attack was already on its way.

That is why a record of your own attacks is more useful than any general list. Our guide to identifying your migraine triggers shows how to look for patterns without becoming anxious about everything, and what to write in a migraine diary covers the basics.

What does science still not know?

There is still a lot researchers cannot yet explain. That does not mean your migraines are mysterious or imaginary: it means the science is still catching up.

Open questions include:

What starts an attack. Experts debate whether it begins in deep brain areas, in the cortex, or in both, and why it begins at one moment and not another.
Why aura happens in some people only. Cleveland Clinic says the exact reason the spreading wave occurs is unknown.
Why people differ so much. Two people with the same genes and triggers can have very different attacks.
Which parts matter most for each person. CGRP helps many people, but not everyone, which suggests other pathways are involved too.

Good science separates what is shown from what is only suggested. What is well supported: the nervous system is involved, the trigeminal pathway and CGRP matter, and genes raise risk. What is less settled: the exact starting point, and how all the pieces fit together.

What does this mean for you day to day?

Understanding the mechanism will not make migraines disappear, but it can make them feel less like a personal failing. Your brain is simply more sensitive, and that is not your fault.

A few practical takeaways:

Look for patterns, not single culprits. A migraine often follows several things stacking up, such as poor sleep plus stress plus a skipped meal.
Notice early signs. Yawning, tiredness or cravings may be part of the early phase, not the trigger.
Talk to a doctor about what fits you. Preventive and acute treatments work on different parts of this chain, and only a professional can advise what suits you.

If a headache is sudden and severe, comes with new symptoms such as weakness or confusion, or feels unlike your usual pattern, seek medical help. Our guide to when to go to the ER for a migraine explains the warning signs. And if you are curious how common all this is, see migraine by the numbers.

Frequently asked questions

What is the main cause of migraine?

There is no single proven cause. Migraine is thought to result from abnormal brain activity that temporarily affects nerve signals, brain chemicals and blood vessels, in people who are genetically more sensitive, according to the NHS. Triggers then tip that sensitive system into an attack.

Is migraine caused by blood vessels or by the nerves?

Current thinking puts the nervous system first. Blood vessels do change during an attack, but Mayo Clinic points to the brainstem, the trigeminal nerve and chemical messengers such as serotonin and CGRP as key parts of the process.

Can stress cause migraine?

Stress is a common trigger, but it is not the underlying cause. It can set off an attack in a brain that is already prone to migraine, which is why the same stressful week affects some people and not others. See stress and migraines for more.

If my mum has migraine, will I get it too?

Not necessarily. Having a parent with migraine raises your likelihood, and Cleveland Clinic notes that most people with migraine have a close relative with it, but many genes and your environment both play a part. Many people with a family history never develop migraine.

Sources

Written by Laurine Nicoletti, founder of Mellow, who has lived with migraine since she was 21. Learn more · How we write our articles

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