Most headaches are caused by tension in the muscles of your scalp, neck, and jaw, or by changes in the blood vessels and nerves inside your skull. The vast majority aren’t dangerous, but the type of pain, where you feel it, and how long it lasts can tell you a lot about what’s going on and what to do about it.
What’s Actually Happening Inside Your Head
Your brain itself can’t feel pain. It has no pain receptors. What hurts are the structures surrounding it: blood vessels, the protective membranes covering the brain (called meninges), and the network of nerves that runs through your face and scalp. The main player is the trigeminal nerve, which branches across your forehead, cheeks, and jaw. When something irritates the blood vessels or membranes near the brain’s surface, the trigeminal nerve fires pain signals through the brainstem and up to the brain’s pain-processing centers.
During a headache, nerve fibers release powerful chemicals that dilate blood vessels and trigger inflammation in the membranes around the brain. One of those chemicals, called CGRP, is one of the most potent dilators of blood vessels inside the skull. This inflammation doesn’t reach the brain itself, which stays protected behind the blood-brain barrier, but the swelling and pressure on the surrounding tissue is what you feel as pain.
The Most Common Headache Types
Tension headaches are by far the most frequent. They feel like a tight band squeezing around your head, producing mild to moderate pain on both sides. They’re usually triggered by stress, poor posture, clenching your jaw, or staring at a screen too long. Most resolve within a few hours.
Migraines are different. The pain is throbbing and pulsing, typically on one side of your head, and it gets worse with physical activity, bright lights, loud sounds, or strong smells. Many migraines are preceded by a visual disturbance called an aura, which happens when a wave of abnormal electrical activity rolls across the brain’s surface. That wave releases inflammatory molecules into the surrounding membranes, essentially kickstarting the headache. Migraines can last anywhere from four hours to three days.
Cluster headaches are less common but far more intense. They produce severe, piercing pain around one eye or the temple on one side. Each episode lasts 15 minutes to three hours and can strike up to eight times a day, often at the same time each day, for weeks or months at a stretch. People with cluster headaches also tend to have lower levels of melatonin during active bouts, which may explain why attacks frequently happen during sleep.
Everyday Triggers You Might Not Suspect
Dehydration
When your body loses more fluid than it takes in, the resulting shift in fluid balance can cause the brain to pull slightly away from the skull. This puts traction on the pain-sensitive membranes and blood vessels surrounding the brain, producing a dull, aching headache that often worsens when you stand up or move around. Drinking water steadily throughout the day is one of the simplest ways to prevent recurring headaches.
Caffeine Withdrawal
If you regularly drink coffee or tea and then skip a day, a headache can start within 12 to 24 hours of your last dose. The pain typically peaks between 20 and 51 hours and can drag on for two to nine days. This happens because caffeine narrows blood vessels in the brain; without it, those vessels dilate, triggering pain. The fix is either to taper your intake gradually or to have a small amount of caffeine to take the edge off.
Poor Sleep
Both too little and too much sleep can trigger headaches. People with sleep apnea, a condition where breathing repeatedly stops and starts during sleep, wake up with headaches about three to four times more often than the general population. If you regularly wake up with head pain, disrupted breathing at night is worth investigating. Even without apnea, inconsistent sleep schedules can throw off the brain chemicals that regulate pain sensitivity.
Weather Changes
Many people blame sinus pressure from changing weather for their headaches, but the evidence tells a more interesting story. Routine shifts in barometric pressure don’t actually cause sinus inflammation. Instead, those weather changes appear to trigger migraines, and the sinus pressure and facial discomfort people feel are symptoms of the migraine itself, not a separate sinus problem. True sinus-related pressure headaches happen only with extreme pressure changes, like during scuba diving or air travel.
When Painkillers Become the Problem
If you reach for over-the-counter pain relief frequently, the medication itself can start causing headaches. This is called medication overuse headache, and it’s more common than most people realize. The threshold depends on the type of painkiller. For basic options like acetaminophen and ibuprofen, using them 15 or more days per month for three months or longer can trigger the cycle. For combination painkillers or prescription migraine medications, the threshold is lower: 10 or more days per month.
The pattern is unmistakable. You take a painkiller, the headache goes away, but it comes back sooner and sooner, so you take more, and the cycle deepens. Breaking it usually means stopping the overused medication, which temporarily makes headaches worse before they improve.
Which Painkiller Works Best
For a standard tension headache, ibuprofen at 400 mg is the most effective over-the-counter option. A large analysis comparing common painkillers found that ibuprofen was nearly three times more likely than a placebo to leave people pain-free at two hours. Acetaminophen at 1,000 mg also works, but it ranked lower in head-to-head comparisons. Naproxen performed the worst among common options.
If ibuprofen bothers your stomach, acetaminophen is a reasonable second choice. But for pure effectiveness against tension headache pain, ibuprofen has the strongest evidence behind it.
Headaches That Need Urgent Attention
Most headaches are harmless, but certain features signal something potentially serious. A sudden, explosive headache that reaches maximum intensity within a minute, sometimes called a thunderclap headache, can indicate bleeding in the brain and needs emergency evaluation. The same goes for a headache paired with fever, confusion, a stiff neck, weakness on one side of the body, or vision changes.
Other warning signs to take seriously:
- New headaches starting after age 65, which have a higher chance of being caused by a serious underlying condition
- Headache after a head injury, especially if it worsens over hours
- Headache that changes dramatically in pattern, frequency, or severity over a short period
- Pain that worsens when you stand up and disappears when you lie down, which can indicate low spinal fluid pressure
- Headache triggered by coughing, sneezing, or straining, which can occasionally point to structural problems at the base of the skull
- A progressively worsening headache that doesn’t respond to typical treatment and keeps getting worse over days or weeks
A headache in someone with a weakened immune system or a history of cancer also warrants prompt medical evaluation, since the risk of infection or metastasis is higher in those groups.