Headaches hurt because pain-sensitive structures surrounding your brain, not the brain itself, become irritated or inflamed. Your brain tissue has no pain receptors at all. The pain you feel during a headache comes from a network of nerves, blood vessels, and membranes in and around your skull that are very much capable of sending distress signals. About 65% of adults worldwide experience at least one active headache disorder, making this one of the most common forms of pain humans deal with.
Your Brain Can’t Feel Pain
This is the part that surprises most people. The brain itself has zero pain receptors. A neurosurgeon can touch brain tissue during an operation and the patient feels nothing. So when your head throbs during a headache, the pain is coming from the structures that surround and protect the brain.
The main pain-sensitive structures inside your skull are the meninges (the layered membranes wrapping the brain), blood vessels on and near the brain’s surface, and the thin lining called the dura mater. For decades, the dura mater and the major blood vessels were considered the only intracranial structures capable of generating pain. More recent research has found that even smaller brain arteries and the innermost membrane, the pia mater, may also be pain-sensitive.
How Pain Signals Travel From Your Head to Your Brain
The trigeminal nerve is the main highway for head pain. It’s the largest nerve in your skull, splitting into three branches that cover different territories of your face, jaw, and the membranes inside your head. When something irritates pain-sensitive structures in or around your skull, free nerve endings on the trigeminal nerve’s fibers pick up the signal.
Those signals travel along two types of nerve fibers. Faster, insulated fibers carry sharp, immediate pain. Slower, uninsulated fibers carry the dull, aching pain that tends to linger. Both types route through a cluster of nerve cell bodies called the trigeminal ganglion, then into the brainstem. From the brainstem, the signal gets relayed up to the thalamus, which acts as a switchboard, and finally to the parts of your brain that process both the physical sensation and the emotional unpleasantness of pain. That last part is important: headache pain isn’t just a physical signal. It’s processed through emotional brain regions too, which is why a bad headache can make you feel miserable in a way that goes beyond simple discomfort.
What Happens During a Tension Headache
Tension-type headaches are the most common variety, affecting roughly a third of adults globally. They typically produce a pressing or tightening sensation on both sides of the head, often described as a band squeezing around the skull.
The pain appears to start in the muscles and connective tissue around the skull. Tenderness in these tissues correlates with both the intensity and frequency of tension headaches, and studies show increased muscle stiffness in people who get them regularly. Specific tight, tender spots in the muscles of the head, neck, and shoulders (called trigger points) are significantly more common in tension headache sufferers. These knotted areas of muscle can refer pain across broader regions of the head.
Over time, something more complex can develop. Repeated pain signals from these peripheral trigger points can change how your central nervous system processes pain, lowering your overall pain threshold. This means your brain starts treating normal sensations as painful. People with chronic tension headaches show lower pain thresholds not just in their head, but across their whole body, suggesting the nervous system has become more sensitive overall. Interestingly, the number of trigger points in head and neck muscles increases with age regardless of headache frequency, which suggests they may accumulate as a consequence of repeated headaches rather than being the sole original cause.
What Happens During a Migraine
Migraines affect roughly one in four adults and involve a more complex cascade of events than tension headaches. The current scientific understanding has shifted dramatically over the past few decades. The old theory held that migraines were fundamentally a blood vessel problem: arteries in the head dilated, stretched pain-sensitive nerve endings, and caused throbbing pain. That vascular theory has been largely set aside. Drugs that specifically target blood vessel dilation don’t work well for migraines, which helped researchers realize the blood vessel changes are a consequence of the attack, not its cause.
The modern view is that migraines are primarily a nervous system disorder. The process starts with abnormal activation of the trigeminal nerve system. When these nerve fibers become activated, they release powerful signaling molecules into the surrounding tissue. The most important of these is a peptide called CGRP, which does several things at once: it dilates blood vessels in and around the brain, it triggers an inflammatory response in the meninges, and it causes nearby immune cells called mast cells to release their own inflammatory chemicals. The result is a spreading wave of inflammation around pain-sensitive structures.
Serotonin plays a key role as well. People with migraines tend to have lower levels of serotonin, which normally helps constrict blood vessels and keep pain signaling in check. When serotonin drops, it leaves vasodilating chemicals like nitric oxide unopposed, and CGRP levels rise. This is also why hormonal shifts can trigger migraines: a drop in estrogen during menstruation decreases serotonin by affecting how it’s metabolized, which can set off the whole cascade.
The inflammatory soup around the meninges sensitizes nearby nerve endings, which begin firing at lower thresholds. This is why during a migraine, normal stimuli like light, sound, or even the pulsing of blood through arteries can feel painful. Your pain system has essentially turned up its sensitivity dial.
Why Headache Pain Feels Different Depending on the Type
The location and quality of headache pain depend on which branch of the trigeminal nerve is involved and which structures are irritated. The trigeminal nerve’s three branches each cover a specific territory:
- First branch (V1): Covers the forehead, eyes, and the top of the head. This branch also innervates the brain’s blood vessels, which is why migraines often center around one eye or the temple.
- Second branch (V2): Covers the cheeks, upper jaw, and part of the nose. Sinus headaches hit this territory.
- Third branch (V3): Covers the lower jaw, temples, and parts of the ear.
Pain in the back of the head follows a different path entirely. The structures in the lower rear of the skull are innervated by the upper cervical nerve roots rather than the trigeminal nerve, which is why neck tension and problems at the base of the skull can produce headaches that radiate from the back of the head forward.
Throbbing pain tends to occur when blood vessels are involved, because each heartbeat pulses blood through dilated, inflamed arteries that are now surrounded by sensitized nerve endings. The steady, squeezing pain of a tension headache reflects the more constant input from tight muscles and connective tissue. A sudden, explosive headache (sometimes called a thunderclap headache) signals a rapid change in pressure or blood flow inside the skull, which is why it’s treated as a medical emergency.
When Headache Pain Signals Something Serious
The vast majority of headaches are primary headaches, meaning they are the problem, not a symptom of something else. But secondary headaches, those caused by an underlying condition, do occur and can be dangerous. Clinicians use a screening framework called SNNOOP10 to identify warning signs. The patterns worth knowing include:
- Sudden, explosive onset: A headache that reaches maximum intensity within seconds, especially if it’s the worst headache of your life.
- Neurologic changes: Weakness, vision loss, confusion, difficulty speaking, or decreased consciousness alongside headache.
- New pattern after age 65: A brand-new headache type appearing for the first time later in life.
- Positional component: Pain that dramatically worsens or improves with changes in body position.
- Progressive worsening: A headache that steadily intensifies over days or weeks without relief.
- Fever with headache: Especially with neck stiffness, which can indicate infection of the meninges.
- Headache after head injury: New or worsening pain following trauma.
These patterns don’t automatically mean something is wrong, but they represent situations where the pain may be coming from a structural problem (bleeding, infection, pressure changes, or a mass) rather than from the typical nerve and blood vessel mechanisms behind common headaches.