Various forms of headache, properly called headache disorders, are among the most common disorders of the nervous system. They are pandemic and, in many cases, life-long conditions.

Headache itself is a painful and often disabling feature of a relatively small number of primary headache disorders. It also occurs secondarily to a considerable number of other conditions. A wide range of headache types have been classified in detail by the International Headache Society (table I). The most common among them – tension-type headache (TTH), migraine, cluster headache and the so-called chronic daily headache syndromes – cause substantial levels of disability. Headache has been and continues to be underestimated in scope and scale, and headache disorders remain under-recognized and under-treated throughout the world.

A worldwide problem

Although the epidemiology of headache disorders is only partly documented, taken together, headache disorders are extraordinarily common. Population-based studies have mostly focused on migraine which, although the most frequently studied, is not the most common headache disorder. Other types of headache, such as the more prevalent TTH and sub-types of the more disabling chronic daily headache, have received less attention. Few population-based studies exist for developing countries where limited funding and large and often rural populations, coupled with the low profile of headache disorders compared with other diseases, prevent the systematic collection of information.

In developed countries, Tension Type Headache (TTH) alone affects two-thirds of adult males and over 80% of females. Extrapolation from figures for migraine prevalence and attack incidence suggests that 3000 migraine attacks occur every day for each million of the general population. Less well recognized is the toll of chronic daily headache: up to one adult in 20 has headache every or nearly every day.

Not only is headache painful, but headache disorders are also disabling. Worldwide, according to the World Health Organization (WHO), migraine alone is 19th among all causes of years lived with disability (YLDs). Headache disorders impose recognizable burden on sufferers including sometimes substantial personal suffering, impaired quality of life and financial cost. Repeated headache attacks, and often the constant fear of the next one, damage family life, social life and employment. For example, social activity and work capacity are reduced in almost all migraine sufferers and in 60% of TTH sufferers.

The long-term effort of coping with a chronic headache disorder may also predispose the individual to other illnesses. For example, depression is three times more common in people with migraine or severe headaches than in healthy individuals.

http://www.who.int/mediacentre/factsheets/fs277/en/print.html