You've had a headache before. Everyone has. But have you ever paused mid-throb and wondered what's actually happening inside your skull? The answer is surprisingly counterintuitive — your brain itself can't feel pain. It has no pain receptors at all. So if the organ responsible for sensing everything can't sense its own discomfort, where is all that pain coming from?

The real story involves a complex alarm system of nerves, blood vessels, and chemical signals working together — and sometimes misfiring. Understanding this system won't cure your next headache, but it can help you make sense of your symptoms, talk more clearly with your doctor, and recognize when something deserves closer attention.

The main player in headache pain is the trigeminal nerve — the largest nerve in your skull. Think of it like a three-pronged security system. One branch covers your forehead and eyes, another your cheeks, and a third your jaw. When something irritates any of these branches, they send urgent signals to your brainstem, which interprets them as pain.

Here's what makes headaches tricky: the trigeminal nerve monitors tissues around the brain — the membranes called meninges, the blood vessels on the brain's surface, and muscles in your face and scalp. When these structures are stretched, compressed, or inflamed, the trigeminal nerve fires. Your brain then registers that signal as pain, even though the brain tissue itself isn't hurting. It's like a smoke detector going off in the hallway, not in the room where the fire is.

In tension-type headaches, the most common kind, this alarm often gets triggered by tight muscles in the scalp, neck, or jaw. The trigeminal nerve picks up the distress and amplifies it. In migraines, the system becomes even more sensitive — a process called central sensitization — where the nerve starts reacting to signals it would normally ignore, like light touch or normal blood flow.

Takeaway

Your brain can't feel its own pain. Headaches come from an alarm network surrounding the brain, which means the location of your pain often points to which part of that network is irritated — useful information for you and your doctor.

That pulsing, throbbing quality of a bad headache? It's directly tied to your blood vessels. During a migraine, blood vessels on the brain's surface dilate — they widen. As they expand, they stretch the surrounding tissue and trigger the trigeminal nerve endings wrapped around them. Each heartbeat pushes a wave of blood through those swollen vessels, which is why the pain throbs in rhythm with your pulse.

But dilation is only half the story. The trigeminal nerve, once activated, releases inflammatory chemicals — including a protein called CGRP (calcitonin gene-related peptide). These chemicals cause the blood vessel walls to become inflamed and even more sensitive. This creates a feedback loop: inflammation triggers more nerve firing, which releases more inflammatory chemicals, which causes more inflammation. It's a cycle that can sustain a headache for hours or even days.

This is actually why modern migraine medications work the way they do. Triptans, a common migraine treatment, help constrict those dilated blood vessels and reduce inflammation. Newer drugs called CGRP inhibitors block that specific inflammatory protein, interrupting the feedback loop at its source. Understanding the mechanism helps explain why a simple painkiller sometimes isn't enough — the problem isn't just pain, it's an active inflammatory process.

Takeaway

A throbbing headache isn't random — it's your blood vessels expanding and inflaming in a self-reinforcing loop. Knowing this helps explain why some treatments target inflammation rather than just blocking pain signals.

Most people think of headache triggers as direct causes — you skipped lunch, so you got a headache. But the biology is more nuanced. Think of your nervous system as a cup that's constantly being filled by various stressors: poor sleep, dehydration, hormonal shifts, muscle tension, bright lights, certain foods. A trigger doesn't cause the headache alone. It's the thing that makes the cup overflow.

This explains a maddening experience many headache sufferers share: the same trigger doesn't always produce the same result. You can drink red wine on Friday and feel fine, then have one glass on Tuesday and end up in bed with a migraine. The difference isn't the wine — it's how full your cup was that day. Maybe Tuesday also involved poor sleep and work stress. The wine was just the last drop.

Biologically, triggers work by lowering the threshold at which your trigeminal system fires. Dehydration, for instance, affects blood volume and can subtly change blood vessel tone. Stress hormones like cortisol increase muscle tension and sensitize pain pathways. Skipped meals cause blood sugar fluctuations that affect neurotransmitter balance. None of these alone may be enough. But stack enough of them together, and your nervous system decides it's time to sound the alarm.

Takeaway

A headache trigger is rarely the sole cause — it's the final straw on an already burdened system. Tracking your overall load of stressors, not just individual triggers, gives you a much more accurate picture of what's really going on.

Headaches aren't mysterious punishments from your body. They're the predictable result of a protective system — nerves, blood vessels, and chemical signals — doing what it was designed to do, sometimes too enthusiastically. Understanding that system puts you in a better position to describe your symptoms accurately and ask better questions.

Next time a headache hits, you'll know what's behind the throb. And the next time you sit across from a doctor, you'll speak a little more of the same language. That understanding is worth more than any quick fix.