Headache is the symptom of pain in the face, head, or neck. It can occur as a migraine, tension-type headache, or cluster headache. There is an increased risk of depression in those with severe headaches.

Headaches can occur as a result of many conditions. There are a number of different classification systems for headaches. The most well-recognized is that of the International Headache Society. Causes of headaches may include dehydration, fatigue, sleep deprivation, stress, the effects of medications and recreational drugs, including withdrawal, viral infections, loud noises, common colds, head injury, rapid ingestion of a very cold food or beverage, and dental or sinus issues (such as sinusitis).

Treatment of a headache depends on the underlying cause, but commonly involves pain medication. A headache is one of the most commonly experienced of all physical discomforts.

About half of adults have a headache in a given year. Tension headaches are the most common, affecting about 1.6 billion people (21.8% of the population) followed by migraine headaches which affect about 848 million (11.7%).

 

Note:   The above text is excerpted from the Wikipedia article Headache, which has been released under the GNU Free Documentation License.