system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 why we have headaches.
gpt
A headache is a pain sensed in the nerves and muscles of the head and neck, as well as the meninges (the membranous coverings of the brain and spinal cord). Your brain itself cannot sense pain, so a headache has nothing to do with your brain hurting. It is really a pain somewhere around your brain, being picked up by nerve endings located in your head.
There are two main reasons why people get headaches, and doctors therefore classify headaches into two broad categories: primary and secondary.
Primary headaches are not associated with any underlying medical condition.
Secondary headaches are associated with medical conditions like infections, fever, head injury, hypoglycemia, tumors, dental conditions or increased pressure in the skull and/or sinuses (sinus headaches).
There are three main causes for primary headaches:
Migraine - Migraine headaches can be caused by reduced blood flow to various areas of the cerebral cortex. Symptoms of migraines include sensitivity to light and noise, nausea, vomiting and intense throbbing pain that is usually on one side of the head. A neurotransmitter, serotonin, is thought to be involved in migraines because many of the drugs used to treat migraines alter the binding of serotonin to various receptors.
Tension - Tension headaches are caused by muscular strains in the head and neck and/or emotional stress. Tension headaches are usually dull, steady, aching pains on both sides of the head. Sometimes, tension headaches develop into throbbing pains, leading researchers to believe that they may be closely related to migraines. Eye strain (poor vision) can trigger frequent tension headaches.
Cluster - Cluster headaches are headaches that occur repeatedly over a period of weeks or even months. Cluster-headache pain usually occurs on one side of the head and is centered around the eye. The causes of cluster headaches are unknown, but may be related to changes in blood flow because substances that affect blood flow, such as alcohol, can trigger cluster headaches.
Primary headaches can also be caused by too much blood flow. For example, if you have read How Caffeine Works, you know that caffeine reduces blood flow in the brain. Some pain relievers contain caffeine to take advantage of this effect. If you have been taking caffeine every day and you stop, you can get an incredible headache because of the increased blood flow in your brain.