If the brain can't feel pain, why do headaches hurt?

Headaches are extremely common and come in many forms, ranging from mild to debilitating and lasting from a few minutes to a few days. When your skull aches, it's easy to assume that your brain tissue itself must be hurting. But that's unlikely.

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Ironically, the brain can feel pain throughout the body but doesn't actually have its own pain receptors. So why do headaches hurt?

Headaches can stem from an underlying medical condition, such as swollen sinuses, low blood sugar, or a head injury. But broadly speaking, most headaches are caused by "referred pain," which means you feel the pain in a different place than where it's actually happening, similar to how a herniated disk in your back can cause sciatica, which is pain in your legs. For most headaches, problems elsewhere in the body — like your jaw, shoulders, and neck — cause pain in the muscles and nerves around your brain.

Take tension headaches, for example, which are the most common type of recurring headache, according to the World Health Organization. Tension headaches typically occur with muscle pain on the top of the head or forehead, where a sweatband or headband sits. The pain is caused by tight muscles in the face, neck, and scalp, and can be stress-related, according to the National Institutes of Health. But there are other theories: Head pain and tight skull muscles can be secondary to another stress response, like tight shoulders or a clenched jaw.

Pain-sensing nerves in the muscles and blood vessels around the head, neck, and face can be triggered by different processes, such as vasodilation, pressure, or muscle tension. Once activated, these nerves send messages to the brain, but it perceives the pain as if it is coming from deep within the brain tissue.

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Migraines are another type of headache, although technically, headaches are just a symptom of a neurological disorder. Migraines can be felt in a variety of ways and locations: deep pain; superficial pain; in the back, left or right side of the head; or behind the eyes. What makes migraines unique is their severity.

Migraines are more intense and last longer than other headaches. The disorder is often hereditary and can cause other symptoms, such as nausea. The root cause of migraines isn't fully understood, but one theory is that the pain is related to the trigeminal nerve, a sensory nerve to the head and face; and the dura mater, a protective covering of the brain where blood vessels expand and contract.

One possible explanation for migraine is that electrical events in the brain stimulate trigeminal nerve pathways and trigger an inflammatory response, which spreads through dural blood vessels, trigeminal nerve fibers carry signals back to the brainstem, and then the inflammation spreads to the pain-sensitive meninges - the protective tissue surrounding the brain - triggering headaches.

This chain of inflamed blood vessels and irritated nerves is "a fire that burns out of control." It's like a feedback loop that gets more and more irritated, leading to a migraine. That's why the sooner you treat a migraine, the better.

While the relationship between pain around the body and pain in the head is well established, the mechanisms that cause headaches are still not fully understood. But there are treatments for these conditions, for example, lifestyle changes, such as practicing yoga; over-the-counter medications, such as ibuprofen and aspirin; and prescription medications for more severe headache disorders can significantly reduce the severity and frequency of headaches.

Source: Chongqing Tianji Network Co., Ltd.

Source: Live Science "If the brain doesn't feel pain, why do headaches hurt?"

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