A person with a headache.
A headache or cephalalgia is pain anywhere in the region of the head or neck. It can be a symptom of a number of different conditions of the head and neck. The brain tissue itself is not sensitive to pain because it lacks pain receptors. Rather, the pain is caused by disturbance of the pain-sensitive structures around the brain. Nine areas of the head and neck have these pain-sensitive structures, which are the cranium (the periosteum of the skull), muscles, nerves, arteries and veins, subcutaneous tissues, eyes, ears, sinuses and mucous membranes.
There are a number of different classification systems for headaches. The most well-recognized is that of the International Headache Society. Headache is a non-specific symptom, which means that it has many possible causes. Treatment of a headache depends on the underlying etiology or cause, but commonly involves analgesics.
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.
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 13 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 ICHD-2 classification defines migraines, tension-types headaches, cluster headache and other trigeminal autonomic cephalalgias as the main types of primary headaches. Also, according to the same classification, stabbing headaches and headaches due to cough, exertion and sexual activity (coital cephalalgia) are classified as primary headaches. The daily-persistent headaches along with the hypnic headache and thunderclap headaches are considered primary headaches as well.
Secondary headaches are classified based on their etiology and not on their symptoms. According to the ICHD-2 classification, the main types of secondary headaches include those that are due to head or neck trauma such as whiplash injury, intracranial hematoma, post craniotomy or other head or neck injury. Headaches caused by cranial or cervical vascular disorders such as ischemic stroke and transient ischemic attack, non-traumatic intracranial hemorrhage, vascular malformations or arteritis are also defined as secondary headaches. This type of headaches may also be caused by cerebral venous thrombosis or different intracranial vascular disorders. Other secondary headaches are those due to intracranial disorders that are not vascular such as low or high pressure of the cerebrospinal fluid pressure, non-infectious inflammatory disease, intracranial neoplasm, epileptic seizure or other types of disorders or diseases that are intracranial but that are not associated with the vasculature of the central nervous system. ICHD-2 classifies headaches that are caused by the ingestion of a certain substance or by its withdrawal as secondary headaches as well. This type of headache may result from the overuse of some medications or by exposure to some substances. HIV/AIDS, intracranial infections and systemic infections may also cause secondary headaches. The ICHD-2 system of classification includes the headaches associated with homeostasis disorders in the category of secondary headaches. This means that headaches caused by dialysis, high blood pressure, hypothyroidism, and cephalalgia and even fasting are considered secondary headaches. Secondary headaches, according to the same classification system, can also be due to the injury of any of the facial structures including teeth, jaws, or temporomandibular joint. Headaches caused by psychiatric disorders such as somatization or psychotic disorders are also classified as secondary headaches.
The ICHD-2 classification puts cranial neuralgias and other types of neuralgia in a different category. According to this system, there are 19 types of neuralgias and headaches due to different central causes of facial pain. Moreover, the ICHD-2 includes a category that contains all the headaches that cannot be classified.
Although the ICHD-2 is the most complete headache classification there is and it includes frequency in the diagnostic criteria of some types of headaches (primarily primary headaches), it does not specifically code frequency or severity which are left at the discretion of the examiner.
The NIH classification consists of brief definitions of a limited number of headaches.
The NIH system of classification is more succinct and only describes five categories of headaches. In this case, primary headaches are those that do not show organic or structural etiology. According to this classification, headaches can only be vascular, myogenic, cervicogenic, traction and inflammatory.
There are over 200 types of headaches, and the causes range from harmless to life-threatening. The description of the headache, together with findings on neurological examination, determines the need for any further investigations and the most appropriate treatment.
Primary headaches 
The most common types of headache are the "primary headache disorders", such as tension-type headache and migraine. They have typical features; migraine, for example, tends to be pulsating in character, affecting one side of the head, associated with nausea, disabling in severity, and usually lasts between 3 hours and 3 days. Rarer primary headache disorders are trigeminal neuralgia (a shooting face pain), cluster headache (severe pains that occur together in bouts), and hemicrania continua (a continuous headache on one side of the head).
Secondary headaches 
Headaches may be caused by problems elsewhere in the head or neck. Some of these are not harmful, such as cervicogenic headache (pain arising from the neck muscles). Medication overuse headache may occur in those using excessive painkillers for headaches, paradoxically causing worsening headaches.
A number of characteristics make it more likely that the headache is due to potentially dangerous secondary causes; some of these may be life-threatening or cause long-term damage. A number of "red flag" symptoms therefore means that a headache warrants further investigations, usually by a specialist. The red flag symptoms are a new or different headache in someone over 50 years old, headache that develops within minutes (thunderclap headache), inability to move a limb or abnormalities on neurological examination, mental confusion, being woken by headache, headache that worsens with changing posture, headache worsened by exertion or Valsalva manoeuvre (coughing, straining), visual loss or visual abnormalities, jaw claudication (jaw pain on chewing that resolves afterwards), neck stiffness, fever, and headaches in people with HIV, cancer or risk factors for thrombosis.
"Thunderclap headache" may be the only symptom of subarachnoid hemorrhage, a form of stroke in which blood accumulates around the brain, often from a ruptured brain aneurysm. Headache with fever may be caused by meningitis, particularly if there is meningism (inability to flex the neck forward due to stiffness), and confusion may be indicative of encephalitis (inflammation of the brain, usually due to particular viruses). Headache that is worsened by straining or a change in position may be caused by increased pressure in the skull; this is often worse in the morning and associated with vomiting. Raised intracranial pressure may be due to brain tumors, idiopathic intracranial hypertension (IIH, more common in younger overweight women) and occasionally cerebral venous sinus thrombosis. Headache together with weakness in part of the body may indicate a stroke (particularly intracranial hemorrhage or subdural hematoma) or brain tumor. Headache in older people, particularly when associated with visual symptoms or jaw claudication, may indicate giant cell arteritis (GCA), in which the blood vessel wall is inflamed and obstructs blood flow. Carbon monoxide poisoning may lead to headaches as well as nausea, vomiting, dizziness, muscle weakness and blurred vision. Angle closure glaucoma (acute raised pressure in the eyeball) may lead to headache, particularly around the eye, as well as visual abnormalities, nausea, vomiting and a red eye with a dilated pupil.
The brain itself is not sensitive to pain, because it lacks pain receptors. However, several areas of the head and neck do have nociceptors, and can thus sense pain. These include the extracranial arteries, large veins, cranial and spinal nerves, head and neck muscles and the meninges.
Headache often results from traction to or irritation of the meninges and blood vessels. The nociceptors may also be stimulated by other factors than head trauma or tumors and cause headaches. Some of these include stress, dilated blood vessels and muscular tension. Once stimulated, a nociceptor sends a message up the length of the nerve fiber to the nerve cells in the brain, signaling that a part of the body hurts.
It has been suggested that the level of endorphins in one's body may have a great impact on how people feel headaches. Thus, it is believed that people who suffer from chronic headaches or severe headaches have lower levels of endorphins compared to people who do not complain of headaches.
Primary headaches are even more difficult to understand than secondary headaches. Although the pathophysiology of migraines, cluster headaches and tension headaches is still not well understood, there have been different theories over time which attempt to provide an explanation of what exactly happens within the brain when individuals suffer from headaches. One of the oldest such theories is referred to as the vascular theory which was developed in the middle of the 20th century. The vascular theory was proposed by Wolff and it described the intracranial vasoconstriction as being responsible for the aura of the migraine. The headache was believed to result from the subsequent rebound of the dilatation of the blood vessels which led to the activation of the perivascular nociceptive nerves. The developers of this theory took into consideration the changes that occur within the blood vessels outside the cranium when a migraine attack occurs and other data that was available at that time including the effect of vasodilators and vasoconstrictors on headaches.
The neurovascular approach towards primary headaches is currently accepted by most specialists. According to this newer theory, migraines are triggered by a complex series of neural and vascular events. Different studies concluded that individuals who suffer from migraines but not from headache have a state of neuronal hyperexcitability in the cerebral cortex, especially in the occipital cortex. People who are more susceptible to experience migraines without headache are those who have a family history of migraines, women, and women who are experiencing hormonal changes or are taking birth control pills or are prescribed hormone replacement therapy.
Diagnosis approach 
|Differential diagnosis of headaches|
|Tension headache||New daily persistent headache||Cluster headache||Migraine|
|mild to moderate dull or aching pain||severe pain||moderate to severe pain|
|duration of 30 minutes to several hours||duration of at least four hours daily||duration of 30-minutes to 3 hours||duration of 4 hours to 3 days|
|Occur in periods of 15 days a month for three months||may happen multiple times in a day for months||periodic occurrence; several per month to several per year|
|located as tightness or pressure across head||located on one or both sides of head||located one side of head focused at eye or temple||located on one or both sides of head|
|consistent pain||pain describable as sharp or stabbing||pulsating or throbbing pain|
|no nausea or vomiting||nausea, perhaps with vomiting |
|no aura||no aura||auras|
|uncommonly, light sensitivity or noise sensitivity||may be accompanied by running nose, tears, and drooping eyelid, often only on one side||sensitivity to movement, light, and noise|
|exacerbated by regular use of acetaminophen or NSAIDS||may exist with tension headache|
While, statistically, headaches are most likely to be primary (non serious 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. Electroencephalograms have not been found to be useful in working up this symptom.
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. People over the age of 50 years may also warrant a CT scan.
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. Research comparing acupuncture to 'sham' acupuncture has shown that the results of acupuncture may be due to the placebo effect.
One type of treatment, however, is usually not sufficient for chronic sufferers and they may have to find a variety of different ways of managing, living with, and seeking treatment of chronic daily headache pains.
There are however two types of treatment for chronic headaches, i.e. acute abortive treatment and preventive treatment. Whereas the first is aimed to relieve the symptoms immediately, the latter is focused on controlling the headaches that are chronic. For this reason, the acute treatment is commonly and effectively used in treating migraines and the preventive treatment is the usual approach in managing chronic headaches. The primary goal of preventive treatment is to reduce the frequency, severity, and duration of headaches. This type of treatment involves taking medication on a daily basis for at least 3 months and in some cases, for over 6 months. The medication used in preventive treatment is normally chosen based on the other conditions that the patient is suffering from. Generally, medication in preventive treatment starts at the minimum dosage which increases gradually until the pain is relieved and the goal achieved or until side effects appear.
To date, only amitriptyline, fluoxetine, gabapentin, tizanidine, topiramate, and botulinum toxin type A (BoNTA) have been evaluated as "prophylactic treatment of chronic daily headache in randomized, double-blind, placebo-controlled or active comparator-controlled trials. Antiepileptics can be used as preventative treatment of chronic daily headache and includes Valproate.
Psychological treatments are usually considered in comorbid patients or in those who are unresponsive to the medication.
Primary headaches account for more than 90% of all headache complaints, and of these, episodic tension-type headache is the most common.
It is estimated that women are three times more prone than men to suffer from migraines. Also, the prevalence of this particular type of headache seems to vary depending on the specific area of the world where one lives. However, migraines appear to be experienced by 12% to 18% of the population.
Cluster headaches are thought to affect less than 0.5% of the population, though their prevalence is hard to estimate because they are often mistaken for a sinusal problem. However, according to the existent data, cluster headaches are more likely to occur in men than women, given that the condition tends to affect 5 to 8 times more men.
The first recorded classification system that resembles the modern ones was published by Thomas Willis, in De Cephalalgia in 1672. In 1787 Christian Baur generally divided headaches into idiopathic (primary headaches) and symptomatic (secondary ones), and defined 84 categories.
Children can suffer from the same types of headaches as adults do although their symptoms may vary. Some kinds of headaches include tension headaches, migraines, chronic daily headaches, cluster headache and sinus headaches. Dental braces and orthodontic headgear (due to the constant pressure placed on the jaw area) are also known for causing occasional to frequent headaches in adolescents. It is actually common for headaches to start in childhood or adolescence, for instance, 20% of adults who suffer headaches report that their headaches started before age 10 while 50% report they started before age 20. The incidence of headaches in children and adolescents is very common. One study reported that 56% of boys and 74% of girls between 12 and 17 indicated having experienced a form of headache within the past month.
The causes of headaches in children include either one factor or a combination of factors. Some of the most common factors include genetic predisposition, especially in the case of migraine; head trauma, produced by accidental falls; illness and infection, for example in the presence of ear or sinus infection as well as colds and flu; environmental factors, which include weather changes; emotional factors, such as stress, anxiety, and depression; foods and beverages, caffeine or food additives; change in sleep or routine pattern; loud noises. Also, excess physical activity or sun may be a trigger specifically of migraine.
Although most cases of headaches in children are considered to be benign, when they are accompanied with other symptoms such as speech problems, muscle weakness, and loss of vision, a more serious underlying cause may be suspected: hydrocephalus, meningitis, encephalitis, abscess, hemorrhage, tumor, blood clots, or head trauma. In these cases, the headache evaluation may include CT scan or MRI in order to look for possible structural disorders of the central nervous system.
Some measures can help prevent headaches in children. Some of them are drinking plenty of water throughout the day; avoiding caffeine; getting enough and regular sleep; eating balanced meals at the proper times; and reducing stress and excess of activities.
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Further reading 
- Gorman, Christine; Park, Alice (7 October 2002). The New Science of Headaches. Time. Retrieved 22 February 2010
- National Headache Foundation
- IHS - The International Headache Classification (ICHD-2)
- American Headache Society
- Withdrawal related headache information
- HealthyCase - Headache or Cephalalgia
- All About Headaches Infographic