A headache is not the brain hurting. The brain itself has no pain receptors. What you feel during a headache is pain generated by the structures surrounding the brain: blood vessels, muscles, nerves, and membranes that line the skull. Depending on which structures are involved and how they’re activated, the experience can range from a dull squeeze around your forehead to a blinding, one-sided throb that leaves you unable to function. Headaches split into two broad camps, primary and secondary, and the distinction matters more than most people realize.
Why the Brain Itself Does Not Hurt
You can poke brain tissue during surgery and the patient won’t feel a thing. The pain-sensitive structures sit outside or on the surface of the brain. Classic experiments on human subjects showed that cranial blood vessels, particularly the large arteries at the base of the brain and along its surface, are the main structures capable of producing headache when stretched, compressed, or inflamed.1JAMA Surgery. EXPERIMENTAL STUDIES ON HEADACHE: PAIN-SENSITIVE STRUCTURES OF THE HEAD AND THEIR SIGNIFICANCE IN HEADACHE The meninges (the membranes wrapping the brain), the periosteum of the skull, and the muscles and skin covering it all carry nerve endings that transmit pain signals. Distending, pulling, or chemically irritating any of these structures is what generates the sensation we call a headache.
The nerve pathways carrying those pain signals converge primarily through the trigeminal nerve, the fifth cranial nerve responsible for sensation across most of the face and scalp. Arteries above a dividing membrane called the tentorium send pain signals through the trigeminal nerve, while arteries below it route signals through the upper cervical nerves.1JAMA Surgery. EXPERIMENTAL STUDIES ON HEADACHE: PAIN-SENSITIVE STRUCTURES OF THE HEAD AND THEIR SIGNIFICANCE IN HEADACHE This wiring explains why some headaches are felt in the forehead or temples and others seem to radiate from the back of the head or neck.
Primary Versus Secondary Headaches
Primary headaches are the condition itself. Nothing else is wrong; the headache disorder is the disease. Tension-type headache, migraine, and cluster headache are all primary. Secondary headaches, by contrast, are symptoms of something else: a sinus infection, a neck injury, medication overuse, or occasionally something dangerous like a bleed in the brain. The overwhelming majority of headaches people experience are primary, but the secondary category is where the serious warning signs hide.
Tension-Type Headache
Tension-type headache is the most common headache in the general population. It feels like a band of pressure around the head, usually on both sides, without the nausea or light sensitivity that comes with migraine. Intensity is typically mild to moderate. The name suggests tight muscles are the whole story, but the reality is more layered. Both the muscles around the skull and the central nervous system play a role.2PubMed. The role of pericranial muscles in the succesful management of episodic tension type headache
The most consistently documented physical finding in people with tension-type headache is increased tenderness of the muscles and connective tissues around the skull. When those tissues stay irritated for a long time, the pain signals they send can change how the central nervous system processes pain. The spinal cord and brainstem structures that receive those signals become hypersensitive, amplifying pain even after the original muscle irritation has improved.3PubMed. Central sensitization in tension-type headache–possible pathophysiological mechanisms This is believed to be a key reason episodic tension headaches sometimes evolve into a chronic daily pattern. Prolonged irritation from the muscles sensitizes the nervous system, and once that sensitization takes hold, it can sustain itself.4PubMed. Muscular factors are of importance in tension-type headache
Migraine
Migraine is far more than a bad headache. It’s a neurological disorder with distinct phases. Many people experience a prodrome (mood changes, food cravings, neck stiffness) hours before the pain hits. About a quarter of migraine sufferers also get an aura, a period of visual disturbances like flashing lights, zigzag lines, or blind spots that typically lasts under an hour. The leading explanation for aura is cortical spreading depression, a slow wave of intense nerve-cell activity followed by suppression that sweeps across the surface of the brain.5PubMed. Pathophysiology of the migraine aura. The spreading depression theory
The pain phase of migraine is driven by what researchers call the trigeminovascular system. Nerve fibers from the trigeminal nerve wrap around blood vessels in the meninges. When those fibers activate, they release a signaling molecule called CGRP (calcitonin gene-related peptide). CGRP dilates blood vessels, promotes inflammation around the meninges, and sensitizes nearby nerve endings, creating a feedback loop of pain.6PubMed Central. CGRP and the Trigeminal System in Migraine The discovery that CGRP is released during migraine attacks and that blocking it relieves pain has been one of the most productive findings in headache medicine. It led directly to a new class of preventive treatments: monoclonal antibodies that either neutralize CGRP itself or block its receptor.7PubMed Central. Migraine and the trigeminovascular system-40 years and counting
Migraine attacks can last anywhere from four hours to three days. The pain is usually one-sided and pulsating, made worse by routine physical activity. Nausea, vomiting, and extreme sensitivity to light and sound are hallmarks. People who’ve never had migraine often underestimate how disabling it is. During an attack, many sufferers can do nothing but lie in a dark, quiet room.
Cluster Headache
Cluster headache is rarer than migraine or tension-type headache, but its intensity is legendary. Attacks produce severe, stabbing pain behind or around one eye, lasting anywhere from fifteen minutes to three hours. Unlike migraine, where people tend to lie still, cluster headache often causes restlessness. People pace, rock, or bang their heads against walls. The pain almost always comes with autonomic symptoms on the same side: a drooping eyelid, tearing, nasal congestion, or a constricted pupil.8PubMed Central. Cluster Headache: Epidemiology, Pathophysiology, Clinical Features, and Diagnosis
The name refers to the pattern. Attacks cluster together in bouts lasting weeks or months, separated by remission periods that can last a year or more. The timing is strikingly regular: attacks often strike at the same hour, frequently waking people from sleep. This clockwork quality pointed researchers toward the hypothalamus, the brain’s master timekeeper. Brain imaging studies found that during a cluster attack, the hypothalamus on the same side as the pain is activated. That activation is absent between bouts.9PubMed. Hypothalamic activation in cluster headache attacks Structural imaging also shows subtle enlargement of gray matter in that same hypothalamic region, suggesting cluster headache involves a built-in abnormality rather than a purely episodic malfunction.10PubMed. Hypothalamic involvement and activation in cluster headache
Secondary Headaches and Common Misdiagnoses
Secondary headaches have an identifiable outside cause. The list is enormous: infections, head injuries, vascular problems, neck disorders, sinus disease, medication overuse, and many others. Some of these are trivial. A headache from a hangover or from skipping your morning coffee counts as secondary. But some are medical emergencies.
A particularly common misdiagnosis deserves mention. Many people with migraine are told they have “sinus headaches.” One study found that over 80% of migraine patients had initially been misdiagnosed with sinusitis, and the average delay before they received a correct migraine diagnosis was nearly eight years.11PubMed Central. Migraine misdiagnosis as a sinusitis, a delay that can last for many years The confusion arises because migraine can cause nasal congestion, facial pressure, and watery eyes, mimicking sinus disease. True sinus headache caused by acute bacterial sinusitis typically involves fever, thick discolored discharge, and pain that worsens when bending forward. If you’ve been treated repeatedly for “sinus headaches” without relief, migraine is worth considering.
Medication overuse headache is another secondary type that sneaks up on people. If you take pain relievers for headaches on more than about ten to fifteen days a month, the medication itself can start generating headaches. Opioids, triptans, combination analgesics containing caffeine or barbiturates, and even common over-the-counter painkillers can all cause this pattern.12PubMed Central. Pathophysiology of medication overuse headache: insights and hypotheses from preclinical studies The treatment is counterintuitive: you have to stop the overused medication. The rebound headaches initially get worse before they improve.
Neck problems can also refer pain into the head. The nerve pathways from the upper cervical spine converge with the trigeminal nerve’s pathways in the brainstem, which means a structural issue in the upper neck can produce pain felt in the face, temples, or forehead.13PubMed. Cervicogenic headache: diagnostic evaluation and treatment strategies These cervicogenic headaches are often one-sided and can be triggered or worsened by certain neck movements.
Warning Signs That Demand Urgent Attention
Most headaches, even severe ones, are not dangerous. But certain features signal a secondary cause that requires emergency evaluation. Neurologists use a systematic screening framework (called SNNOOP10) to flag headaches that need investigation beyond the clinical exam.14PubMed Central. Red and orange flags for secondary headaches in clinical practice: SNNOOP10 list You don’t need to memorize the acronym, but you should know the red flags:
- Thunderclap onset: A headache that reaches its worst intensity within a minute. The most dangerous cause is subarachnoid hemorrhage, a bleed around the brain, but it can also signal blood vessel spasm, clots, or other vascular emergencies.15PubMed. The Thunderclap Headache: Approach and Management in the Emergency Department
- Worst headache of your life: Especially if it is unlike anything you’ve experienced before.
- Neurological symptoms: Weakness, numbness, confusion, vision loss, difficulty speaking, or seizures accompanying a headache.
- Fever and stiff neck: This combination may point to meningitis or another central nervous system infection.
- New headache after age 50: Especially if accompanied by scalp tenderness, jaw pain while chewing, or visual disturbance, which can indicate giant cell arteritis, an inflammatory disease of blood vessels that can cause permanent vision loss if untreated.16PubMed Central. Visual Manifestations in Giant Cell Arteritis: Trend over Five Decades in a Population-based Cohort
- Progressive worsening: A headache that gets steadily worse over days or weeks rather than coming and going.
- Headache triggered by coughing, exertion, or sexual activity: These sometimes have benign causes, but imaging is generally recommended to rule out structural problems.
Thunderclap headache deserves special emphasis because the stakes are so high. Subarachnoid hemorrhage carries serious risk of death or lasting disability, and the diagnosis can be missed if a patient is sent home after the pain improves. The standard evaluation includes a CT scan of the brain, and if that scan is normal, a lumbar puncture or additional vascular imaging to rule out bleeds and other causes.17PubMed. Thunderclap headache: an update If you experience a headache that hits like a clap of thunder, go to an emergency department even if the pain subsides on its own.
Giant cell arteritis is another condition where delay can be devastating. Once vision loss occurs from the vessel inflammation, it is permanent.18BMJ. Long delay from symptom onset to first consultation contributes to permanent vision loss in patients with giant cell arteritis: a cohort study Prompt treatment with corticosteroids can prevent that outcome, but only if the condition is recognized in time.
When Imaging Is and Isn’t Needed
A common concern for headache sufferers is whether they need a brain scan. The evidence is clear that most people with an uncomplicated, recurring primary headache pattern and a normal neurological exam do not need imaging. Scans become warranted when any of the red flags above are present, when the headache pattern suddenly changes, or when the headache is triggered by coughing, exertion, or sexual activity.19Journal of the American College of Radiology. ACR Appropriateness Criteria Headache If your doctor says you don’t need a scan for a longstanding headache that fits a typical migraine or tension-type pattern, that decision is well supported by guidelines. The scan wouldn’t change your treatment.
Hormonal Triggers and Menstrual Migraine
Hormones are one of the clearest and most studied headache triggers. Roughly 60% of women with migraine report a link between their attacks and menstruation.20PubMed. Hormonal changes throughout life in women The driver appears to be the drop in estrogen levels that happens in the days just before a period. Estrogen influences the trigeminovascular system that underlies migraine pain, and the withdrawal of estrogen seems to lower the threshold for an attack.21PubMed Central. Menstrual migraine is caused by estrogen withdrawal: revisiting the evidence The same pattern shows up during the hormone-free interval of oral contraceptive pills and in the postpartum period, both times when estrogen levels drop sharply.
This hormonal connection helps explain why migraine is roughly three times more common in women than men after puberty, while rates are roughly equal in childhood. It also explains why some women find their migraines improve after menopause, when hormonal cycling stops, though others find the transition years leading up to menopause are actually worse because of erratic hormone fluctuations.
The Gut Connection
A growing area of research links the gut microbiome to migraine susceptibility. The gut communicates with the brain through several pathways including the vagus nerve, immune signaling molecules, and metabolites produced by gut bacteria. Disruptions in gut microbiome composition may influence neuroinflammation and alter the balance of neurotransmitters in ways that lower the threshold for migraine attacks.22PubMed Central. The Brain, the Eating Plate, and the Gut Microbiome: Partners in Migraine Pathogenesis This is still early-stage science, and nobody should expect a probiotic to cure migraine. But it does help explain why dietary factors and gastrointestinal symptoms so often accompany migraine, and it’s an active target for future therapies.
Migraine Without Headache in Children
One of the more surprising facts about headache disorders is that they don’t always involve head pain, especially in children. Abdominal migraine causes recurrent bouts of moderate to severe belly pain, nausea, and pallor in kids who are perfectly healthy between episodes. It affects roughly 1 to 4% of children and is diagnosed clinically based on the pattern of attacks.23PubMed Central. Review of Abdominal Migraine in Children Cyclical vomiting syndrome is a related condition featuring episodes of intense, repeated vomiting. Both are considered “migraine equivalents” because they share features with migraine and because many affected children eventually go on to develop typical migraine headaches as they get older.24PubMed. Abdominal migraine and cyclical vomiting syndrome
These conditions are easy to miss or misattribute to food intolerances or anxiety. A child with recurrent episodes of vomiting or unexplained abdominal pain who is completely fine in between should be evaluated with migraine equivalents in mind. The episodic, stereotyped pattern and the absence of symptoms between attacks are the giveaway. If neurological symptoms accompany the vomiting, or if vomiting doesn’t bring relief, a neurology evaluation is especially warranted to rule out structural causes.25PubMed. Neurological Etiologies and Pathophysiology of Cyclic Vomiting Syndrome
New Treatment Approaches
Headache treatment has changed substantially in the past decade, particularly for migraine. The CGRP-targeting drugs mentioned earlier represent the first class of medications designed specifically for migraine prevention. Four monoclonal antibodies are available: three that bind the CGRP molecule itself and one that blocks its receptor. They are given as monthly or quarterly injections and reduce the number of headache days per month.26PubMed Central. Advances in CGRP Monoclonal Antibodies as Migraine Therapy: A Narrative Review A related class of small-molecule drugs called gepants block the same CGRP pathway but come in pill form. Gepants can be used both for acute treatment during an attack and for prevention, making them unusually versatile.27PubMed. Targeting CGRP for migraine treatment: mechanisms, antibodies, small molecules, perspectives
For people who prefer drug-free options or who can’t tolerate medications, non-invasive neuromodulation devices are another emerging option. Several FDA-cleared devices stimulate nerves in the scalp, forehead, neck, or arm using electrical pulses or magnetic fields. These devices are safe, well tolerated, and free of drug interactions, making them particularly appealing for people already taking multiple medications or for pregnant women.28PubMed Central. Update on Neuromodulation for Migraine and Other Primary Headache Disorders: Recent Advances and New Indications The International Headache Society has recognized these devices as promising alternatives to drug treatment for both acute and preventive management of migraine.29PubMed. International Headache society evidence-based guidelines on the use of non-invasive neuromodulation devices for the acute and preventive treatment of migraine The effect sizes tend to be modest compared to the strongest medications, but the near-absence of side effects makes them a practical first step for many patients.