Headache is defined as a pain arising from the head or upper neck of the body. The pain originates from the tissues and structures that surround the skull or the brain because the brain itself has no nerves that give rise to the sensation of pain (pain fibers). The thin layer of tissue (periosteum) that surrounds bones, muscles that encase the skull, sinuses, eyes, and ears, as well as thin tissues that cover the surface of the brain and spinal cord (meninges), arteries, veins, and nerves, all can become inflamed or irritated and cause headache. The pain may be a dull ache, sharp, throbbing, constant, intermittent, mild, or intense.
In 2005, the International Headache Society released its latest classification system for headache. Because so many people suffer from headaches and because treatment sometimes is difficult, it was hoped that the new classification system would help health care professionals make a specific diagnosis as to the type of headache and allow better and more effective options for treatment.
The society has a 2013 revised 3rd edition (beta) headache publication online but it has as of yet not been finalized.
There are three major categories of headache based upon the source of the pain: