A headache is pain felt anywhere in the head, and it’s one of the most common health complaints on the planet. In 2023, an estimated 2.9 billion people worldwide had a headache disorder, roughly 35% of the global population. Despite how universal the experience is, what’s actually happening inside your head during a headache is less obvious than you might think.
Why Your Head Hurts (It’s Not Your Brain)
Your brain itself has no pain receptors. You could poke brain tissue directly and feel nothing. The pain you experience during a headache comes from the structures surrounding the brain: the meninges (thin layers of tissue wrapping the brain), blood vessels running along the brain’s surface, and the nerves threaded through these tissues. When these structures are stretched, compressed, inflamed, or chemically irritated, they send pain signals through the trigeminal nerve, a large nerve that branches across your face, forehead, and scalp. That signal reaches your brainstem and registers as head pain.
This is why headaches can feel so different from one another. The specific tissue involved, the type of irritation, and where along the nerve pathway the signal originates all shape whether the pain is dull and squeezing, sharp and stabbing, or throbbing in rhythm with your pulse.
Primary vs. Secondary Headaches
Headaches fall into two broad categories. Primary headaches are the condition itself. Nothing else is wrong; the pain system in your head is misfiring or overreacting on its own. Tension-type headaches, migraines, and cluster headaches are all primary headaches. They account for the vast majority of headaches people experience.
Secondary headaches are a symptom of something else: a sinus infection, dehydration, a hangover, a head injury, high blood pressure, or in rare cases, something more serious like bleeding in the brain. The headache goes away when the underlying cause is treated.
Tension-Type Headaches
This is the headache most people picture when they hear the word. It feels like a band of dull pressure or tightness across the forehead, sometimes extending to the sides and back of the head. The pain is usually mild to moderate, affects both sides, and doesn’t throb. You won’t feel nauseous, and light and sound don’t typically bother you the way they do with a migraine.
An episode can last anywhere from 30 minutes to a full week. Some people get them a few times a month (episodic), while others have them more days than not (chronic), sometimes for hours at a stretch. Stress, poor sleep, eye strain, and muscle tension in the neck and shoulders are common triggers, though the exact mechanism isn’t fully understood.
Migraines
Migraines are more than a bad headache. They involve a cascade of neurological events that produces moderate to severe throbbing pain, usually on one side of the head, often accompanied by nausea, vomiting, and intense sensitivity to light, sound, or smells. An untreated attack typically lasts 4 to 72 hours.
The process starts when the trigeminal nerve system becomes activated and releases a signaling molecule called CGRP from nerve endings around the brain’s blood vessels. CGRP triggers inflammation in the meninges, causes blood vessels to widen, and sensitizes nearby pain fibers, creating a feedback loop that amplifies the pain. This is why newer migraine treatments specifically block CGRP and can stop or prevent attacks.
About a quarter of migraine sufferers experience an aura before the pain hits: visual disturbances like zigzag lines, blind spots, or flashing lights, sometimes accompanied by tingling in the face or hands. Aura usually lasts 20 to 60 minutes and then fades as the headache phase begins. Common triggers include hormonal changes, certain foods, alcohol, sleep disruption, weather shifts, and stress (or the letdown after stress).
Cluster Headaches
Cluster headaches are rare but extraordinarily painful. The pain is severe, piercing, and almost always located around or behind one eye. Attacks last between 15 minutes and 3 hours and can happen multiple times a day, anywhere from once every other day to eight times in 24 hours. They arrive in “cluster periods” lasting weeks or months, then disappear for months or even years before returning.
What makes cluster headaches distinctive are the autonomic symptoms that accompany them, all on the same side as the pain: the eye reddens and tears up, the eyelid droops or swells, the nostril gets stuffy or runs, and the forehead may sweat. Unlike migraine sufferers who want to lie still in a dark room, people with cluster headaches typically feel agitated and restless during an attack, pacing or rocking.
Medication Overuse Headaches
One of the most counterintuitive headache problems is that the very medications you take to relieve headaches can start causing them if used too often. This happens when you take pain relievers more than a couple of days per week on a regular basis. The threshold depends on the medication: combination painkillers (those mixing caffeine, aspirin, and acetaminophen), opioids, and migraine-specific drugs called triptans carry a higher risk and can trigger rebound headaches at 10 or more days of use per month. Simple over-the-counter painkillers like ibuprofen or acetaminophen alone have a lower risk, but using them more than 15 days a month for three months or longer can still lead to the same problem.
The result is a cycle: your headaches become more frequent, so you take more medication, which makes them more frequent still. Breaking the cycle usually requires gradually stopping the overused medication, which can temporarily worsen headaches before they improve.
Common Triggers and Contributing Factors
Across headache types, several triggers show up repeatedly. Dehydration, skipped meals, poor or inconsistent sleep, alcohol (especially red wine), caffeine withdrawal, prolonged screen time, and emotional stress are among the most common. Hormonal shifts explain why women experience migraines at roughly two to three times the rate of men, particularly around menstruation.
Environmental factors matter too. Weather changes, strong smells, bright or flickering lights, and loud noise can all provoke headaches in susceptible people. Keeping a headache diary for a few weeks, tracking when episodes hit and what preceded them, is one of the simplest ways to identify your personal triggers.
Treating a Headache Safely
For most tension-type headaches, over-the-counter options work well when used sparingly. Acetaminophen and ibuprofen are both effective for mild to moderate pain. The key safety limit for acetaminophen is 4,000 milligrams (four grams) in a 24-hour period, and exceeding that, especially over time, risks liver damage. Ibuprofen and similar anti-inflammatory drugs can cause stomach and kidney issues with heavy use.
Non-medication approaches often help just as much. A cold or warm compress on the forehead or neck, a short nap in a quiet dark room, staying hydrated, and gentle stretching of the neck and shoulders can relieve a mild headache without pills. For people with frequent headaches, regular exercise, consistent sleep schedules, stress management, and limiting caffeine intake tend to reduce how often episodes occur.
Warning Signs That Need Urgent Attention
Most headaches are harmless, but certain patterns signal something potentially dangerous. A sudden, explosive headache that reaches maximum intensity within seconds, sometimes called a thunderclap headache, can indicate bleeding around the brain and needs immediate evaluation. New neurological symptoms alongside a headache, such as weakness on one side of the body, new numbness, confusion, difficulty speaking, or vision changes (beyond a typical migraine aura you’ve experienced before), are also red flags.
Other concerning signs include a headache accompanied by fever and stiff neck, a new type of headache starting after age 50, headaches that steadily worsen over days or weeks, and headaches that change intensity when you shift positions or strain. A new headache during or shortly after pregnancy also warrants evaluation, as it can point to vascular or hormonal complications. None of these patterns are guaranteed to mean something serious, but they fall outside the normal behavior of primary headaches and deserve a prompt medical assessment.