Headaches affect roughly 40% of the global population, about 3.1 billion people, and they arise from a surprisingly wide range of causes. The brain itself has no pain receptors. Instead, headache pain comes from pain-sensitive structures surrounding it: the scalp, the lining of the skull (called the meninges), blood vessels, and muscles in the head and neck. When these structures are irritated, compressed, inflamed, or stretched, the trigeminal nerve and upper cervical nerves carry pain signals that you experience as a headache.
Understanding which structures are involved helps explain why so many different things, from skipping water to sleeping in an awkward position, can all produce the same basic symptom.
Tension, Posture, and Muscle Strain
The most common type of headache is a tension-type headache, and it typically feels like a tight band of pressure around the forehead or the sides and back of the head. It often starts with tightness in the muscles of the neck, shoulders, or jaw. Sitting hunched over a screen for hours, clenching your teeth, or sleeping with poor neck support can all set it off.
When the problem originates specifically in the upper neck, it’s called a cervicogenic headache. The top three vertebrae in your spine (C1 through C3), along with their surrounding joints, ligaments, and nerve roots, are tightly connected to nerves that also serve the head. Pain from a stiff or injured neck gets “referred” upward, so you feel it in your head even though the source is your spine. This is why a headache that always seems to start on one side and worsens when you move your neck may actually be a neck problem in disguise.
Dehydration and Missed Meals
When your body loses more fluid than it takes in, the concentration of salts and minerals in your blood rises. This shift pulls water out of surrounding tissues, including the brain. As the brain loses volume slightly, it can tug on the meninges and the blood vessels attached to them. These structures are rich in pain receptors, and that traction is enough to trigger a headache. Dehydration headaches often feel dull and get worse when you stand up, bend over, or move your head quickly.
Skipping meals works through a related but different pathway. Low blood sugar causes blood vessels in the brain to expand as the body tries to maintain adequate fuel delivery, and that dilation activates pain-sensitive nerve endings. The fix for both is straightforward: steady fluid intake throughout the day and regular meals.
Food and Drink Triggers
Certain chemicals in food are well-established headache triggers, especially for people prone to migraines.
- Alcohol triggers inflammation within the pain-signaling system of the head and promotes dilation of blood vessels in the meninges. This explains why even moderate drinking can cause a headache before you’d consider yourself hungover.
- Tyramine is found in aged cheese, cured meats, smoked fish, fermented foods, and beer. Your body normally breaks it down quickly, but some people metabolize it more slowly, leading to a spike in blood pressure and headache.
- Nitrates, common in processed meats like hot dogs and deli meats, can cause two waves of headache: a mild one within an hour of eating, and a more severe, migraine-like headache three to six hours later.
- Caffeine is a double-edged trigger. Regular use causes your blood vessels to adapt, so when you skip your usual coffee, vessels dilate and produce a withdrawal headache. But caffeine in moderation can also relieve headaches, which is why it’s an ingredient in some pain relievers.
Interestingly, chocolate is often blamed for headaches, but research suggests cocoa may actually suppress the release of pain-signaling molecules in the trigeminal nerve system. The craving for chocolate before a migraine may be an early symptom of the attack itself, not the cause.
Sleep, Stress, and Hormones
Too little sleep, too much sleep, and irregular sleep schedules all increase headache frequency. Sleep disruption affects the brain’s ability to regulate pain signaling, lowering the threshold at which normal stimuli become painful. Stress works through a similar mechanism. Sustained stress keeps muscles in the head and neck contracted and alters levels of brain chemicals involved in pain modulation. Often, a headache hits not during the most stressful moment but in the letdown period afterward, which is why “weekend headaches” are a real phenomenon.
Hormonal shifts play a significant role, particularly for women. Drops in estrogen levels just before or during menstruation are a well-known migraine trigger. Pregnancy, perimenopause, and hormonal contraceptives can all shift headache patterns in either direction.
Weather and Environmental Factors
Many people report headaches when the weather changes, and they often attribute it to sinus pressure. However, research has found no evidence that routine barometric pressure changes cause actual sinus inflammation. The facial pain and pressure that people feel during weather shifts are more likely migraine-related. Migraines can produce congestion and facial pressure that closely mimic sinus symptoms, which is why sinus headaches are frequently misdiagnosed when a migraine is the real culprit.
Bright or flickering lights, strong smells (perfume, paint fumes, cigarette smoke), loud noise, and screen glare are all environmental triggers that can activate the trigeminal nerve directly. Stuffy, poorly ventilated rooms increase carbon dioxide levels, which dilates blood vessels in the brain and can produce a dull headache over the course of hours.
Medication Overuse Headache
One of the most counterintuitive causes of headaches is the very medication you take to treat them. When over-the-counter pain relievers like ibuprofen or acetaminophen are used on 15 or more days per month for three months or longer, they can cause a cycle of daily or near-daily headaches. For combination pain relievers, triptans, and opioid-based medications, the threshold is even lower: 10 or more days per month.
The pattern is predictable. The medication wears off, a headache returns, you take another dose, and gradually the headache-free intervals shrink. The headache itself becomes self-perpetuating. Breaking the cycle requires reducing or stopping the overused medication, which temporarily worsens headaches before they improve. This is a common and underrecognized problem, so if you find yourself reaching for pain relievers most days of the week, the medication itself may be part of the issue.
Underlying Medical Conditions
Most headaches are “primary,” meaning the headache itself is the condition. But secondary headaches are caused by an underlying problem, and the range of possibilities is wide. Common and relatively benign causes include sinus infections, ear infections, dental problems, dehydration, hangovers, and flu or other febrile illnesses. High blood pressure, eye conditions like acute glaucoma, and even tight-fitting headgear can also produce headaches.
More serious causes include concussion, brain aneurysm, blood clots within the brain, meningitis, encephalitis, and stroke. These are uncommon but important to recognize. A spinal headache, caused by low cerebrospinal fluid pressure after a spinal tap or from a spontaneous leak, characteristically worsens when standing and improves when lying flat.
Warning Signs That Need Urgent Attention
Neurologists use a structured checklist to identify headaches that may signal something dangerous. The red flags worth knowing include:
- Sudden, explosive onset: a severe headache that reaches maximum intensity within seconds, sometimes called a “thunderclap headache”
- Neurologic symptoms: confusion, vision changes, weakness on one side, slurred speech, or loss of consciousness
- Fever with headache and stiff neck: a combination that may indicate meningitis or encephalitis
- New headache pattern after age 50: first-time or distinctly different headaches in older adults carry a higher risk of serious underlying causes
- Headache after head injury: especially if it worsens over hours or days
- Progressive worsening: a headache that gets steadily worse over days or weeks rather than coming and going
- Positional component: headaches that dramatically change with standing or lying down can indicate pressure problems inside the skull
- Headache triggered by coughing, sneezing, or straining: occasionally signals a structural issue at the base of the skull
A single headache with any of these features is worth an urgent evaluation. Most will turn out to be benign, but these patterns exist specifically to catch the small percentage that aren’t.