Your brain itself cannot feel pain. It has no pain receptors at all. So when your head throbs during a headache, the pain is coming from the tissues surrounding your brain: blood vessels, muscles, nerves, and the protective membranes wrapped around it. About 35% of adults worldwide experience a headache disorder in any given year, and the underlying mechanism varies depending on the type. But every headache shares a common thread: pain signals from structures outside the brain being relayed inward.
Why Your Brain Can’t Feel Pain
The brain processes pain signals from everywhere else in your body, but it contains no pain-sensing nerve endings of its own. This is why brain surgery can be performed on awake patients. The structures that do sense pain are the ones surrounding and supporting the brain: the meninges (layers of tissue that wrap around the brain and spinal cord), the blood vessels running through and along those membranes, the muscles and skin of the scalp and neck, and the nerves that thread through all of it.
The meninges are especially important. Stimulating the outermost layer, called the dura mater, near its arteries produces pain that closely resembles a migraine, complete with nausea and light sensitivity. The major artery supplying the dura is densely packed with sensory nerve fibers, making it one of the most pain-sensitive structures inside the skull.
How Pain Signals Travel From Head to Brain
The trigeminal nerve is the main highway for headache pain. It’s the largest nerve in your head, with three branches that cover your forehead, cheeks, and jaw. Smaller fibers from this nerve also extend inward to supply the meninges and blood vessels inside the skull. When any of these tissues become irritated, inflamed, or stretched, the trigeminal nerve picks up the signal and relays it to the brainstem, then up to the thalamus (a relay station deep in the brain), and finally to the sensory cortex, where you consciously experience pain.
This pathway explains why a headache can feel like it’s coming from behind your eye, across your forehead, or deep inside your skull, even though the triggering event might be inflammation in a membrane or tension in a muscle. The trigeminal nerve covers a wide territory, and the brain isn’t always precise about pinpointing where along that nerve the signal originated.
How Tension Headaches Work
Tension headaches are the most common type, and they feel like a tight band of pressure around the head. The pain starts in the muscles and connective tissue of the scalp, neck, and shoulders. People with tension headaches consistently have significantly more tenderness in these muscles than people without headaches, and that tenderness correlates directly with both pain intensity and how often headaches occur.
In occasional tension headaches, the problem is mostly peripheral. Muscles tighten, inflammatory chemicals build up around local nerve endings, and those nerve endings become more sensitive to pressure and movement. This is why rubbing your temples or stretching your neck can sometimes help: you’re addressing the source of irritation directly.
Chronic tension headaches, the kind that occur 15 or more days per month, involve a deeper change. The central nervous system itself becomes rewired. Nerve pathways in the brainstem and spinal cord that normally process pain signals start amplifying them instead. Touch and pressure that wouldn’t normally register as painful begin triggering pain responses. People with chronic tension headaches show heightened sensitivity not just in their head and neck, but across their entire body, which indicates the amplification is happening at a high level in the nervous system, not just in local tissues. This shift from a muscle problem to a nervous system problem is a key reason chronic tension headaches are harder to treat than occasional ones.
How Migraines Work
Migraines involve a fundamentally different and more complex mechanism than tension headaches. The process often begins with a wave of electrical activity that sweeps slowly across the surface of the brain, called cortical spreading depression. This wave is a burst of excitation followed by a period of suppressed activity, moving across the cortex like a ripple on water. In people who experience migraine aura (visual disturbances, tingling, or temporary difficulty speaking), this wave is what causes those symptoms. The visual cortex going through its excitation-then-shutdown cycle produces the shimmering zigzag lines or blind spots that many migraine sufferers recognize.
As this electrical wave moves across the brain, it triggers a cascade of chemical events. Nerve fibers in the trigeminal system release a signaling molecule called CGRP, which dilates blood vessels in the meninges and promotes inflammation. Plasma proteins leak from blood vessels in the dura (but not from vessels in the brain itself), creating a localized inflammatory soup around pain-sensitive structures. The blood vessels swell, the surrounding tissue becomes inflamed, and the trigeminal nerve fibers in the area become hypersensitive. This is neurogenic inflammation: inflammation driven by the nervous system rather than by an infection or injury.
The result is throbbing, often one-sided pain that worsens with physical activity, because each heartbeat pulses through those inflamed, swollen vessels. The trigeminal system’s connections to areas controlling nausea, light processing, and sound processing explain why migraines come packaged with sensitivity to light, noise, and stomach upset. These aren’t separate symptoms layered on top of head pain. They’re all downstream effects of the same trigeminal activation.
Why Headaches Throb
The pulsing quality of many headaches, particularly migraines, comes from blood vessels. When arteries in and around the meninges become dilated and inflamed, each pulse of blood stretching the vessel wall activates the pain-sensing nerve fibers wrapped around it. Your heart rate literally sets the rhythm of the pain. This is also why bending over or exerting yourself can make a headache worse: both increase blood flow and blood pressure in the head temporarily, stretching those already irritated vessels further.
What Separates a Harmless Headache From a Dangerous One
Most headaches are primary headaches, meaning the headache itself is the condition, not a symptom of something else. But headaches can also be caused by serious underlying problems like bleeding in the brain, infections, or increased pressure inside the skull. Several warning signs distinguish these dangerous secondary headaches from ordinary ones.
The most alarming is sudden onset. A headache that reaches maximum intensity within seconds, sometimes called a thunderclap headache, can indicate a ruptured blood vessel or aneurysm and needs emergency evaluation. Other red flags include:
- Neurological symptoms: new weakness in an arm or leg, unusual numbness, or vision changes that aren’t typical of your usual headaches
- Systemic signs: fever, night sweats, or unexplained weight loss accompanying the headache
- New headaches after age 50: a first-time headache pattern starting later in life is more likely to have a secondary cause
- Progressive worsening: headaches that are clearly becoming more severe or more frequent over weeks
- Positional changes: pain that shifts dramatically when you stand up, lie down, cough, or strain
Women who develop a new headache pattern during or shortly after pregnancy also warrant evaluation, as pregnancy-related vascular and hormonal changes can produce secondary headaches. The key pattern across all these red flags is novelty and change. A headache that behaves differently from anything you’ve experienced before deserves more attention than one that fits your usual pattern.
Why Some People Get More Headaches Than Others
Headache disorders affect about 37.5% of women and 31.8% of men globally. This sex difference is partly hormonal, as estrogen fluctuations are a well-established migraine trigger, which is why migraines often track with menstrual cycles. But genetics, nervous system sensitivity, and environmental factors all play roles in determining individual susceptibility.
People who develop chronic headaches often undergo a process of central sensitization, where their pain-processing systems gradually become more reactive over time. Repeated headache episodes can lower the threshold for future episodes, creating a cycle where the nervous system becomes progressively easier to trigger. This is one reason headache specialists emphasize managing headaches early and consistently rather than waiting for them to become entrenched. Once the central nervous system has recalibrated its sensitivity upward, reversing that change takes significantly more effort than preventing it.