Headache is pain that occurs anywhere in the head. This includes not only the interior of the head but also the face and the scalp. Most headaches last for several hours, but some may last for weeks. Seven out of 10 people suffer from headache at least once a year, according to the American College of Physicians, and 45 million people in the U.S. have chronic headaches. The International Headache Society distinguishes between headaches that are themselves primary disorders and those for which the cause is some other disorder.
Causes of Migraine Headache
The exact mechanism by which migraines develop remains unclear, but environmental and genetic factors appear to contribute to causing migraine headache, according the Mayo Clinic. One likely cause is changes in a specific nerve--the trigeminal nerve--that plays an important role in transmitting pain signals. Serotonin and other pain-regulating brain chemicals might also play a role in causing migraines. During migraines, reduced levels of serotonin might send a signal to the trigeminal system that causes it to emit neuropeptides. When the neuropeptides reach the meninges--the layer of protective tissues covering the brain--this cause the pain associated with migraine headache.
A number of factors may provide the triggers that set off those migraine-causing processes. Stress, some types of food and sensory signals such as sights and sounds, are possible triggers. Normal fluctuations in hormone levels may trigger migraines in some women.
Causes of Tension-Type Headache
A person may experience tension-type headaches not only in the head but also in the scalp or neck. The person may feel pain or merely discomfort. Tension in, or contraction of, the muscles of these areas cause this type of headache, which is one of the most commonly occurring type of headache, according to Medline Plus, a website of the National Institutes of Health. The muscle tension causing the headache might be due to anxiety, depression, stress or a head injury.
The NIH adds that activities in which the head is held in place for extended periods might cause a tension headache. A typical activity of this type is working at a computer. Other possible triggers are overexertion, fatigue, eye strain and sinus infection.
Causes of Cluster Headache
Cluster headaches are the most severe of the primary headaches, according to the National Institute of Neurological Disorders and Stroke. These headaches commence abruptly and the pain can be so extreme that it wakes people from sleep. While scientists have not yet identified the exact causes of cluster headaches, it seems that they might be linked to a sudden release of either serotonin or histamine. Some possible triggers are bright lights, high altitudes, heat and physical exertion.
Causes of Other Primary Headaches
Some of the other primary headache types identified by the International Headache Society are acute thunderclap headache, sometimes acute sinusitis; primary cough headache, caused as implied by its name, coughing or straining; and primary exertional headache, caused by physical exertion.
Causes of Secondary Headache
The categorization by the International Headache Society for the secondary headaches identifies the causes of these headaches in the names of the categories. Those categories include headache caused by trauma to the head and or the neck, which includes whiplash; and headache caused by an infection, such as bacterial meningitis.
Causes of Other Headaches
The third overall International Headache Society category--cranial neuralgias, central and primary facial pain and other headaches--mentions headaches causes, including exposure of the head to low temperatures and headache caused by compression of cranial nerves.
References
- International Headache Society: International Classification of Headache Disorders, 2nd Edition
- The Merck Manuals: Approach to the Patient With Headache
- National Institute of Neurological Disorders and Stroke: NINDS Headache Information Page
- Medline Plus: Headache
- American College of Physicians: Headaches
