What is a Headache?

In medicine a headache or cephalalgia is a symptom of a number of different conditions of the head. Some of the causes are benign while others are medical emergencies.

There are a number of different classification systems for headaches. The most well-recognized is that of the International Headache Society.

Treatment of a headache depends on the underlying etiology or cause, but commonly involves analgesics.

Headache Classification

The first recorded classification system that resembles the modern ones was published by Thomas Willis, in ''De Cephalagia'' in 1672. In 1787 Christian Baur generally divided headaches into idiopathic (primary headaches) and symptomatic (secondary ones), and defined 84 categories.

Today headaches are most thoroughly classified by the International Headache Society's, International Classification of Headache Disorders (ICHD), which published the second edition in 2004. This classification is accepted by the WHO.

Other classification systems exist. One of the first published attempts was in 1951. The National Institutes of Health developed a classification system in 1962.

Headaches can also be classified by severity and acuity of onset. Headaches that are both severe and acute are known as thunderclap headaches.


The International Classification of Headache Disorders (ICHD) is an in-depth hierarchical classification of headaches published by the International Headache Society. It contains explicit (operational) diagnostic criteria for headache disorders. The first version of the classification, ICHD-1, was published in 1988. The current revision, ICHD-2, was published in 2004.

The classification uses numeric codes. The top, one-digit diagnostic level includes 14 headache groups. The first four of these are classified as primary headaches, groups 5-12 as secondary headaches, cranial neuralgia, central and primary facial pain and other headaches for the last two groups.


The NIH classification consists of brief definitions of a limited number of headaches.

While, statistically, headaches are most likely to be primary (harmless and self-limiting), some specific secondary headache syndromes may demand specific treatment or may be warning signals of more serious disorders. Differentiating between primary and secondary headaches can be difficult.

As it is often difficult for patients to recall the precise details regarding each headache, it is often useful for the sufferer to fill-out a "headache diary" detailing the characteristics of the headache.


When the headache does not clearly fit into one of the recognized primary headache syndromes or when atypical symptoms or signs are present then further investigations are justified. Neuroimaging (noncontrast head CT) is recommended if there are new neurological problems such as decreased level of consciousness, one sided weakness, pupil size difference, etc or if the pain is of sudden onset and severe, or if the person is known HIV positive.

Chronic headaches

In recurrent unexplained headaches keeping a "headache diary" with entries on type of headache, associated symptoms, precipitating and aggravating factors may be helpful. This may reveal specific patterns, such as an association with medication, menstruation or absenteeism or with certain foods.

It was reported in March 2007 by two separate teams of researchers that stimulating the brain with implanted electrodes appears to help ease the pain of cluster headaches.

Acupuncture has been found to be beneficial in chronic headaches of both tension type and migraine type. Whether or not there is a difference between true acupuncture and sham acupuncture however is yet to be determined.

Headache Epidemiology

During a given year, 90% of people suffer with headaches. Of the ones who are seen in the ER, about 1% have a serious underlying problem.

Last Updated: Nov 21, 2009

Read in | English | Español | Français | Deutsch | Português | Italiano | 日本語 | 한국어 | 简体中文 | 繁體中文 | العربية | Dansk | Nederlands | Filipino | Finnish | Ελληνικά | עִבְרִית | हिन्दी | Bahasa | Norsk | Русский | Svenska | Magyar | Polski | Română | Türkçe
The opinions expressed here are the views of the writer and do not necessarily reflect the views and opinions of News-Medical.Net.
Post a new comment
You might also like... ×
Paracetamol safety and osteoarthritis: an interview with Professor David Hunter, University of Sydney