The first thing that might surprise you is that what causes headaches isn’t related to anything going on in your brain—in fact, your brain doesn’t feel pain, because it doesn’t have any pain receptors (the nerve endings that are found throughout the body, and that transmit pain signals). But your head, face, and neck do have these pain receptors, in arteries, muscles, and spinal nerves, among others. If there’s any over-activity or dysfunction in these areas, they can play a key role in what causes headaches.
If you’ve ever typed “headache behind eye” into your browser, it’s likely you’re suffering from a migraine headache. These headaches cause severe throbbing pain that tends to affect the front or one side of the head (hence, “headache behind eye”), and is worsened by movement. You also may notice an “aura” before your migraine symptoms start; an aura is a visual disturbance like flashing lights, or zigzag lines across your field of vision. Other migraine symptoms may include nausea, vomiting, light sensitivity, and blurred vision.
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A number of other factors can contribute to migraine headaches:
- Genetics: Some 90 percent of migraine sufferers have a family history of migraine symptoms.
- Stress, anxiety, depression: Not only can these factors cause muscle tension, they also can affect the way you perceive and cope with pain.
- Hormonal changes—for example, changes in hormones and hormonal levels during the menstrual cycle.
- Bright or flashing lights: These can trigger migraines particularly if you’re tired or have been drinking alcohol.
- Hunger: It is possible that low blood sugar due to not eating might be linked to migraines.
- Dehydration: It is thought that lack of fluid causes your blood volume to drop, which reduces the amount of oxygen flowing to the brain.
- Fatigue that may be the result of an underlying sleep disorder, such as sleep apnea.
- Bipolar disorder: Several studies link migraines to this mood disorder.
- Epilepsy: People with seizure disorders are twice as likely to suffer from migraines.
- Asthma. The link is thought to be due to the fact migraines and asthma both involve inflammation.
- Diet: Chocolate, aged cheese, processed meats, monosodium glutamate (commonly used in Chinese food), red wine, and caffeine could contribute to headaches.
- Strong odors: Sensitivity to perfume and more offensive odors (such as cigarette smoke) is more likely in migraine sufferers who also have depression.
- Overexertion: Some people who suffer from migraines report that they find relief if they switch from high-intensity exercise to low-intensity exercise.
- Medication overuse: Taking too many painkillers can cause migraine symptoms to flare up again once medications wear off
- Changing weather: Some research suggests that thunderstorms can be migraine causes, though it isn’t clear why.
A tension headache is the most common type of headache, but they aren’t as severe as migraines. You’ll feel tension headaches as constant pressure or squeezing at both sides of your head, rather than pulsing, throbbing pain at the front or just one side of your head.
Some tension headache causes are the same as for migraines. Tension headache causes can include the following factors:
- Stress, anxiety, and depression
- Hunger, and dehydration
- Bad posture
- Arthritis in the vertebrae of the neck, since the nerves that link to your scalp originate from these vertebrae.
- Temporomandibular joint disorder (TMJD): This affects the jaw joints, and you may have the condition if you notice popping, clicking and/or grating sounds when you open your mouth wide (for example, during a dental exam). TMJD is more common in people who clench or grind their teeth, and in those who have arthritis. If you think your tension headache causes may include TMJD, ask your dentist to fit you with a biteguard you can wear at night.
- Eye strain: This is particularly common if you work on a computer and don’t take frequent breaks. Your tension headache also may be caused by eyestrain if you are squinting due to wearing the wrong-strength glasses, so be sure to get your vision checked regularly.
These occur on a daily basis, at the same time of the day or night, with a “cluster” typically lasting for about six to 12 weeks, with periods of remission in between. Like migraine, a cluster headache may be preceded by an aura, and tend to be focused on one side of the head. Cluster headache causes include the following:
- Genetics: About 20 percent of cluster headache sufferers have a family history of the condition.
- A problem in the hypothalamus. This part of the brain controls many bodily functions, including your heart rate, blood pressure, temperature, appetite, and sleep cycles. Imaging tests have revealed increased activity in the hypothalamus during a cluster headache.
- Tobacco use: Two-thirds of sufferers smoke, or have smoked in the past.
- Nitroglycerin: This medication is used to treat heart disease.
This type of headache is caused by headache medication overuse, and often occur first thing in the morning, since painkillers taken the night before will have worn off overnight. Rebound headache causes include these medications:
- Most painkillers taken for headaches have the potential to cause rebound headaches.
- Analgesics like acetaminophen (Tylenol) and medications that combine acetaminophen, aspirin, and caffeine (for example, Excedrin) carry more risk for rebound headaches than NSAIDs like ibuprofen (Advil, Motrin) and naproxen (Aleve, Naprosyn).
Other headache causes include colds and flu, sinusitis (inflamed sinuses), a head injury (always tell your doctor if you have sustained one of these), and carbon monoxide poisoning (install a carbon monoxide alarm in your home).
For further reading, see the following University Health News posts:
Originally published in 2016, this post is regularly updated.