Migraines are so painful because they involve a chain reaction across your nervous system that ordinary headaches never trigger. A regular tension headache involves muscle tightness around the skull. A migraine, by contrast, activates the trigeminal nerve, the largest sensory nerve in your head, which sets off inflammation around your brain’s protective membranes, dilates blood vessels, and progressively rewires your pain processing so that even normal sensations become excruciating. The headache phase alone can last up to three days.
The Trigeminal Nerve Fires First
The pain of a migraine begins when the trigeminal nerve, which supplies sensation to your face, eyes, and the membranes surrounding your brain, becomes activated. This nerve sends signals through a network of mostly unmyelinated fibers (nerve fibers without insulation, which transmit slow, burning pain) that connect to pain-sensitive structures inside your skull: the dura mater (the tough membrane wrapping your brain), the large blood vessels on the brain’s surface, and the venous sinuses that drain blood from your head.
These peripheral nerve fibers converge in a relay station in the upper brainstem and neck called the trigeminal cervical complex. From there, the pain signal gets handed off to second-order neurons deeper in the brainstem, then to the thalamus, and finally up to the cortex where you consciously experience pain. This multi-layered relay system is why migraine pain feels so deep, diffuse, and difficult to escape. It’s not coming from one spot you can rub or stretch away. It’s being amplified at every stage of transmission.
Inflammation Around the Brain
Once the trigeminal nerve fires, its endings release a flood of inflammatory neuropeptides directly onto the blood vessels and membranes surrounding your brain. The most important of these is calcitonin gene-related peptide, or CGRP. This molecule binds to receptors on smooth muscle cells in blood vessel walls, forcing them to dilate and increasing blood flow through the meningeal vasculature. Other released peptides break down the walls of tiny blood vessels, causing plasma to leak into surrounding tissue, producing swelling and edema.
Both types of neuropeptides also trigger mast cells (immune cells embedded in tissue) to release their own inflammatory contents, creating a self-reinforcing loop. The result is a state called neurogenic inflammation: the dura and the blood vessels running along it become swollen, chemically irritated, and hypersensitive to any mechanical stimulation. This is why the pain throbs in time with your heartbeat. Each pulse of blood stretches inflamed vessel walls that are now far more sensitive to pressure than they should be. It’s also why coughing, bending over, or any physical activity makes the pain worse, since those actions increase pressure inside your skull.
Your Pain System Turns Up the Volume
What makes migraines uniquely brutal, compared to other painful conditions, is a process called sensitization. It happens in stages, and each stage makes the pain harder to control.
First, the inflamed nerve endings around your dural blood vessels become hypersensitive to mechanical pressure. This is peripheral sensitization, and it explains the pulsating quality of the pain and why head movements intensify it. But the process doesn’t stop at the periphery.
Next, the second-order neurons in the brainstem, the ones receiving signals from those now-hyperactive nerve endings, start overreacting to normal inputs. At this point, touching your scalp, combing your hair, or resting your head on a pillow can feel painful. This is called cephalic allodynia: pain from a stimulus that shouldn’t hurt at all.
In severe attacks, sensitization reaches the third-order neurons in the thalamus, which process sensory information from your entire body. When this happens, you can develop extracephalic allodynia, where even wearing a watch, having clothing touch your arms, or pressure on your legs feels uncomfortable. Your whole nervous system has effectively turned up its pain dial. This progressive sensitization is a key reason why treating migraines early, before central sensitization sets in, tends to work better than waiting.
Why Light and Sound Make It Worse
Most people with migraines experience photophobia (sensitivity to light) and phonophobia (sensitivity to sound), and these aren’t just annoyances. They’re evidence that the brain’s sensory processing has gone haywire. During a migraine, the brain loses its normal ability to filter and dampen incoming sensory signals. Neuroimaging studies show that people who get migraines with aura have increased connectivity and heightened activity in the visual cortex, even between attacks. During an attack, this hyperexcitability means ordinary room lighting or background conversation registers as painfully intense.
The connection between aura and light sensitivity appears to share a common mechanism: the same underlying brain excitability that produces the visual disturbances of an aura also predisposes the visual cortex to amplify normal light into something unbearable. This sensory overload doesn’t just happen alongside the pain. It feeds into the same sensitized neural circuits, making the overall experience feel more overwhelming.
Cortical Spreading Depression and Aura
About one in four people with migraines experience aura, typically visual disturbances like zigzag lines, blind spots, or shimmering arcs that develop over five minutes or more and last up to an hour (sometimes longer). These symptoms are caused by cortical spreading depression: a slow wave of intense electrical activity that rolls across the brain’s surface, followed by a period of suppressed activity.
This electrical wave doesn’t just cause visual symptoms. It directly activates the trigeminal system and triggers the release of CGRP from trigeminal nerve endings. In other words, for people who get aura, cortical spreading depression acts as an ignition switch for the entire inflammatory pain cascade described above. The aura is not separate from the headache. It’s the opening act that kicks the trigeminal system into gear.
Genetics Load the Gun
Migraine runs in families, and the reason is largely genetic. Most common migraines are polygenic, meaning dozens or hundreds of small genetic variations each contribute a small amount of risk. These variants tend to affect ion channels (the gates that control electrical signaling in nerve cells), neurotransmitter systems, and vascular function, all of which influence how excitable your brain is and how readily the trigeminal system activates.
Researchers have identified several genes that appear across migraine subgroups, including ones involved in synaptic signaling and cellular stress responses. One rare but instructive form, familial hemiplegic migraine, involves mutations in specific ion channel genes that directly control how sodium, potassium, and calcium flow through nerve cells. These mutations make neurons dramatically more prone to firing, which helps explain why some families experience unusually severe and frequent attacks. While most people’s migraines aren’t caused by a single gene, the same types of ion channel and neurotransmitter pathways are involved across the spectrum, just with subtler variations.
The Full Attack Can Last Days
A migraine is not just a headache. It’s a neurological event that unfolds in up to four distinct phases, and the pain phase is only one of them.
- Prodrome: Hours to days before the headache, you may notice fatigue, mood changes, food cravings, neck stiffness, or difficulty concentrating. These are signs your brainstem and hypothalamus are already shifting into a pre-attack state.
- Aura: If you get aura, it typically lasts 5 to 60 minutes, though about 20% of people experience it for longer.
- Headache: The pain phase lasts from several hours to three days. It’s typically moderate to severe, one-sided, and throbbing, worsened by physical activity.
- Postdrome: After the pain resolves, many people feel drained, foggy, or mildly disoriented for a variable period, sometimes called a “migraine hangover.”
The total experience, from earliest warning signs to full recovery, can stretch across nearly a week. This prolonged timeline reflects just how deeply the entire nervous system is involved.
Why Newer Treatments Target CGRP
Because CGRP plays such a central role in triggering and sustaining migraine pain, it has become the primary target of modern migraine therapies. A class of medications that either block the CGRP molecule itself or block its receptor can now be used both to prevent migraines and to treat them once they start. In clinical trials, roughly half of patients on these treatments achieved at least a 50% reduction in the number of headache days per month, compared with about one-quarter of patients on placebo.
These numbers reflect a meaningful improvement, though they also illustrate that migraine isn’t driven by a single molecule. The pain involves overlapping systems: trigeminal nerve activation, neurogenic inflammation, progressive sensitization, and underlying genetic excitability. Blocking one major player helps many people significantly, but the complexity of the cascade is exactly why migraines remain so difficult to fully eliminate for everyone who gets them.