As of 2013 tension headaches affect about 1.6 billion people (20.8% of the population) and are more common in women than men (23% to 18% respectively). Despite its benign character, tension-type headache, especially in its chronic form, can impart significant disability on patients as well as burden on society at large.

Most patients have persistent headaches, although about 15% will remit, and 8% will have a relapsing-remitting type. It is not infrequent for NDPH to be an intractable headache disorder that is unresponsive to standard headache therapies.

About 65% of persons with CH are, or have been, tobacco smokers. Stopping smoking does not lead to improvement of the condition and CH also occurs in those who have never smoked (e.g. children); it is thought unlikely that smoking is a cause. People with CH may be predisposed to certain traits, including smoking or other lifestyle habits.

In general, children suffer from the same types of headaches as adults do, but their symptoms may be slightly different. The diagnostic approach to headache in children is similar to that of adults. However, young children may not be able to verbalize pain well. If a young child is fussy, they may have a headache.

Approximately 1% of Emergency Department visits for children are for headache. Most of these headaches are not dangerous. The most common type of headache seen in pediatric Emergency Rooms is headache caused by a cold (28.5%). Other headaches diagnosed in the Emergency Department include post-traumatic headache (20%), headache related to a problem with a ventriculoperitoneal shunt (a device put into the brain to remove excess CSF and reduce pressure in the brain) (11.5%) and migraine (8.5%). The most common serious headaches found in children include brain bleeds (subdural hematoma, epidural hematoma), brain abscesses, meningitis and ventriculoperitoneal shunt malfunction. Only 4–6.9% of kids with a headache have a serious cause.

Just as in adults, most headaches are benign, but when head pain is accompanied with other symptoms such as speech problems, muscle weakness, and loss of vision, a more serious underlying cause may exist: 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. If a child with a recurrent headache has a normal physical exam, neuroimaging is not recommended. Guidelines state children with abnormal neurologic exams, confusion, seizures and recent onset of worst headache of life, change in headache type or anything suggesting neurologic problems should receive neuroimaging.

When children complain of headaches, many parents are concerned about a brain tumor. Generally, headaches caused by brain masses are incapacitating and accompanied by vomiting. One study found characteristics associated with brain tumor in children are: headache for greater than 6 months, headache related to sleep, vomiting, confusion, no visual symptoms, no family history of migraine and abnormal neurologic exam.

Some measures can help prevent headaches in children. 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 may prevent headaches. Treatments for children are similar to those for adults, however certain medications such as narcotics should not be given to children.

Children who have headaches will not necessarily have headaches as adults. In one study of 100 children with headache, eight years later 44% of those with tension headache and 28% of those with migraines were headache free. In another study of people with chronic daily headache, 75% did not have chronic daily headaches two years later, and 88% did not have chronic daily headaches eight years later.

Cluster headache may, but rarely, run in some families in an autosomal dominant inheritance pattern. People with a first degree relative with the condition are about 14–48 times more likely to develop it themselves, and between 1.9 and 20% of persons with CH have a positive family history. Possible genetic factors warrant further research, current evidence for genetic inheritance is limited.

Approximately 64–77% of people have a headache at some point in their lives. During each year, on average, 46–53% of people have headaches. Most of these headaches are not dangerous. Only approximately 1–5% of people who seek emergency treatment for headaches have a serious underlying cause.

More than 90% of headaches are primary headaches. Most of these primary headaches are tension headaches. Most people with tension headaches have "episodic" tension headaches that come and go. Only 3.3% of adults have chronic tension headaches, with headaches for more than 15 days in a month.

Approximately 12–18% of people in the world have migraines. More women than men experience migraines. In Europe and North America, 5–9% of men experience migraines, while 12–25% of women experience migraines.

Cluster headaches are very rare. They affect only 1–3 per thousand people in the world. Cluster headaches affect approximately three times as many men as women.

The pathophysiology of NDPH is poorly understood. Research points to an immune-mediated, inflammatory process. Cervical joint hypermobility and defective internal jugular venous drainage have also been suggested as causes.

In 1987, Vanast first suggested autoimmune disorder with a persistent viral trigger for CDH (now referred to as NDPH). Post-infectious origins have been approximated to make up anywhere between 30–80% of NDPH patients in different studies. Viruses that have been implicated include Epstein-Barr virus, herpes simplex virus and cytomegalovirus.

Non-specific upper respiratory infections including rhinitis and pharyngitis are most often cited by patients. In one study, 46.5% patients recalled a specific trigger with a respiratory tract illness being the most common. In children, almost half report headache onset during an infection.

A study by Rozen and Swindan in 2007 found elevated levels of tumor necrosis factor alpha, a proinflammatory cytokine, in the cerebrospinal fluid but not the blood of patients with NDPH, chronic migraine, and post-traumatic headaches suggesting inflammation as the cause of the headaches.

NDPH as an inflammatory, post-infectious manifestation indicates a potential meningoencephalitis event in NDPH patients. Tissue specificity is a general feature of post-infectious, immune-mediated conditions, and the meninges are a type of connective tissue membrane. Inflammation of the meninges was first proposed as a possible pathophysiology for migraine in the 1960s and has recently been explored again. This hypothesis is based on meningeal mast cell activation. Reactive arthritis (ReA) is a post-infectious disease entity of synovium/joints with connective tissue membrane (synovial membrane of the joints) which provides a corollary.

NDPH has been reported in Hashimoto's encephalopathy, an immune-mediated type of encephalitis. A mean 5-year retrospective analysis of 53 patients with a history of viral meningitis and 17 patients with a history of bacterial meningitis showed an increased onset of subsequent new onset headache and increased severity of those with prior primary headaches.

Tension headaches that do not occur as a symptom of another condition may be painful, but are not harmful. It is usually possible to receive relief through treatment. Tension headaches that occur as a symptom of another condition are usually relieved when the underlying condition is treated. Frequent use of pain medications in patients with tension-type headache may lead to the development of medication overuse headache or rebound headache.

Although CPH is often compared to cluster headaches, it is much less prevalent, occurring in only 1–3% of those who experience cluster headaches. CPH occurs roughly in 1 in 50,000 people, while cluster headaches are comparatively more common and are found in 1 in 1000 people.

Cluster headaches occur primarily in men, while CPH is more commonly diagnosed in women. The female to male ratio of diagnosed patients can range anywhere from 1.6:1 to 2.36:1. Symptoms may begin to appear at any age, but onset usually occurs in adulthood with a mean starting age within the thirties.

The pathophysiology of SUNCT is incompletely understood. Recent studies suggest the existence of a relationship between the hypothalamus and the condition.

Functional MRI and deep brain stimulation of a large patient pool showed activation of the posterior hypothalamus during attacks of primary SUNCT, on both sides and contralaterally (on the opposite side). Functional MRI studies suggest brain stem activation during attacks as well. Activation of the trigeminocervical complex and other related structures results from innervation from branches of trigeminal and upper cervical nerves.

There exists a direct connection between trigeminal nucleus caudalis, which is located in the brain stem, and the posterior hypothalamus. Therefore, it is possible that stimulation of the peripheral trigeminal nerve activates the hypothalamus and the hypothalamus in turn communicates with the trigeminal nucleus caudalis via neurotransmitters such as orexin.

Elevated levels of prolactin, secretion of which is regulated by the hypothalamus, seem to be associated with SUNCT attacks. Some patients with a pituitary tumor only experience attacks at night. These patients only exhibit higher levels of prolactin at night, even where hormone levels, including prolactin, were normal throughout the day.

SUNCT is considered a primary headache (or condition), but can also occur as a secondary symptom of other conditions. However, a patient can only be diagnosed with SUNCT as a primary condition.

A pituitary tumor causes SUNCT as a secondary headache. Some patients with a pituitary tumor complain of short-lasting heachaches. Upon removal of the tumor, the symptoms of SUNCT may disappear permanently.

Although it occurs very rarely, paranasal sinusitis can also cause secondary SUNCT. The symptoms of SUNCT in such cases can be removed permanently with endoscopic sinus surgery.

Short-lasting unilateral neuralgiform headache with conjunctival injection and tearing (SUNCT syndrome), is a rare headache disorder that belongs to the group of headaches called trigeminal autonomic cephalalgia (TACs). Symptoms include excruciating burning, stabbing, or electrical headaches mainly near the eye and typically these sensations are only on one side of the body. The headache attacks are typically accompanied by cranial autonomic signs that are unique to SUNCT. Each attack can last from five seconds to six minutes and may occur up to 200 times daily.

TACs are caused by activation of the autonomic nervous system of the trigeminal nerve in the face.

As of 2015 about 50 cases have been described in the medical literature. Onset of the symptoms usually come later in life, at an average age of about 50. Although the majority of patients are men over the age of 50, it is not uncommon to find SUNCT present among other age groups, including children and infants.

Chronic headache, or chronic daily headache (CDH), is classified as experiencing fifteen or more days with a headache per month. It is estimated that chronic headaches affect "4% to 5% of the general population". Chronic headaches consist of different sub-groups, primarily categorized as chronic tension-type headaches and chronic migraine headaches. The treatments for chronic headache are vast and varied. Medicinal and non-medicinal methods exist to help patients cope with chronic headache, because chronic headaches cannot be cured. Whether pharmacological or not, treatment plans are often created on an individual basis. Multiple sources recommend "multimodal treatment", which is a combination of medicinal and non-medicinal remedies. Some treatments are controversial and are still being tested for effectiveness. Suggested treatments for chronic headaches include medication, physical therapy, acupuncture, relaxation training, and biofeedback. In addition, dietary alteration and behavioral therapy or psychological therapy are other possible treatments for chronic headaches.

MOH is known to occur with frequent use of many different medications, including most commonly: triptans, ergotamines, analgesics, opioids. The underlying mechanisms that lead to the development of the condition are still widely unknown and clarification of their role is hampered by a lack of experimental research or suitable animal models. Various pathophysiological abnormalities have been reported and they seem to have an important role in initiating and maintaining chronic headache (genetic disposition, receptor and enzyme physiology and regulation, psychological and behavioural factors, physical dependencies, recent functional imaging results).

A ten-patient study conducted by Pareja et al. found that all patients diagnosed with CPH were responsive to indomethacin and were able to completely control their symptoms. Doses of the drug ranged from 25 mg per day to 150 mg per day with a median dose of 75 mg per 24-hour period.

Almost all cases of CPH respond positively and effectively to indometacin, but as much as 25 percent of patients discontinued use of the drug due to adverse side effects, namely complications in the gastrointestinal tract.

According to a case study by Milanlioglu et al., 100mg of lamotrigine, an antiepileptic drug, administered twice daily alleviated all painful symptoms. No side effects were noted after two months of treatment. Dosage of lamotrigine was decreased to 50mg a day after the first two months, and no symptoms or side-effects were recorded after a three-month followup.

Use of topiramate has also been found to be an effective treatment for CPH, but cluster headache medications have been found to have little effect.

Hemicrania was mentioned in 1881 in The Therapeutic Gazette Vol. 2, by G.S.Davis, and the incident has been cited in King's American Dispensatory (1898 and later editions) in the description of the strong analgesic Jamaican Dogwood, a relatively low dose of which reportedly produced convulsions and prolonged respiratory depression over six hours in an elderly woman with this condition.

In newer times, Hemicrania continua was described in 1981; at that time around 130 cases were described in the literature. However, rising awareness of the condition has led to increasingly frequent diagnosis in headache clinics, and it seems that it is not as rare as these figures would imply. The condition occurs more often in women than men and tends to present first in adulthood, although it has also been reported in children as young as 5 years old.

The International Headache Society's International Classification of Headache Disorders classifies hemicrania continua as a primary headache disorder.

MOH is common and can be treated. The overused medications must be stopped for the patient's headache to resolve. Clinical data shows that the treatment of election is abrupt drugs withdrawal, followed by starting prophylactic therapy. However, the discontinuation of overused drugs usually leads to the worsening of headache and the appearance of drug withdrawal symptoms (that greatly depend on the previously overused drugs and typically last from two to ten days and that are relieved by the further intake of the overused medication), which might reinforce the continuation of overuse. Where physical dependence or a rebound effect such as rebound headache is possible, gradual reduction of medication may be necessary. It is important that the patient's physician be consulted before abruptly discontinuing certain medications as such a course of action has the potential to induce medically significant physical withdrawal symptoms. Abruptly discontinuing butalbital, for example, can actually induce seizures in some patients, although simple over the counter analgesics can safely be stopped by the patient without medical supervision. A long-acting analgesic/anti-inflammatory, such as naproxen (500 mg twice a day), can be used to ease headache during the withdrawal period. Two months after the completion of a medication withdrawal, patients suffering from MOH typically notice a marked reduction in headache frequency and intensity.

Drug withdrawal is performed very differently within and across countries. Most physicians prefer inpatients programmes, however effective drug withdrawal may also be achieved in an outpatient setting in uncomplicated MOH patients (i.e. subjects without important co-morbidities, not overusing opioids or ergotaminics and who are at their first detoxification attempt). In the absence of evidence-based indications, in MOH patients the choice of preventive agent should be based on the primary headache type (migraine or TTH), on the drug side-effect profile, on the presence of co-morbid and co-existent conditions, on patient’s preferences, and on previous therapeutic experiences.

Following an initial improvement of headache with the return to an episodic pattern, a relevant proportion (up to 45%) of patients relapse, reverting to the overuse of symptomatic drugs.

Predictors of the relapse, and that could influence treatment strategies, are considered the type of primary headache, from which MOH has evolved, and the type of drug abused (analgesics, and mostly combination of analgesics, but also drugs containing barbiturates or tranquillisers cause significantly higher relapse rates), while gender, age, duration of disease and previous intake of preventative treatment do not seem to predict relapse rate.

MOH is clearly a cause of disability and, if not adequately treated, it represents a condition of risk of possible co-morbidities associated to the excessive intake of drugs that are not devoid of side-effect. MOH can be treated through withdrawal of the overused drug(s) and by means of specific approaches that focus on the development of a close doctor-patient relationship in the post-withdrawal period.

The most common chronic treatment method is the use of medicine. Many people try to seek pain relief from analgesic medicines (commonly termed pain killers), such as aspirin, acetaminophen, aspirin compounds, ibuprofen, and opioids. The long term use of opioids; however, appears to result in greater harm than benefit. Also, abortive medications can be used to "stop a headache once it has begun"; such drugs include ergotamine (Cafergot), triptans (Imitrex), and prednisone (Deltasone). However, medical professionals advise that abuse of analgesics and abortive medications can actually lead to an increase in headaches. The painkiller medicines help headaches temporarily, but as the "quick fix" wears off, headaches become more re-current and grow in intensity. These "rebound headaches" can actually make the body less responsive to preventive medication. The conditions keep worsening if one takes paracetamol, aspirin and non-steroidal anti-inflammatory drugs (NSAIDs) for 15 days a month or more. Therefore, analgesic and abortive medications are often advised for headaches that are not chronic in nature.

Hypnic headaches are benign primary headaches that affect the elderly, with the average age of onset being 63 ± 11 years. They are moderate, throbbing, bilateral or unilateral headaches that wake the sufferer from sleep once or multiple times a night. They typically begin a few hours after sleep begins and can last from 15–180 min. There is normally no nausea, photophobia, phonophobia or autonomic symptoms associated with the headache. They commonly occur at the same time every night possibly linking the headaches with circadian rhythm, but polysomnography has recently revealed that the onset of hypnic headaches may be associated with REM sleep.

Lithium carbonate 200–600 mg at bedtime is an effective treatment for most patients but for those that can not tolerate Lithium, Verapamil, indomethacin or methylsergilide may be tried. Two patients have also responded to flunarizine 5 mg. It has also been shown that 1–2 cups of coffee or 100–200 mg of caffeine before bed can prevent hypnic headaches.

For diagnosis of hypnic headache syndrome, headaches should occur at least 15 times per month for at least one month. Included in the differential diagnosis of a new onset nighttime headaches in the elderly is drug withdrawal, temporal arteritis, Sleep apnea, oxygen desaturated, Pheochromocytoma, intracranial causes, primary and secondary neoplasms, communicating hydrocephalus, subdural hematoma, vascular lesions, migraines, cluster headaches, chronic paroxysmal hemicrania and hypnic headache. All other causes must be ruled out before the diagnosis of hypnic headache can be made.

There is strong evidence to show that chronic orofacial pain (including AFP) is associated with psychological factors. Sometimes stressful life events appear to precede the onset of AFP, such as bereavement or illness in a family member. Hypochondriasis, especially cancerophobia, is also often cited as being involved. Most people with AFP are "normal" people who have been under extreme stress, however other persons with AFP have neuroses or personality disorders, and a small minority have psychoses. Some have been separated from their parents as children.

Depression, anxiety and altered behavior are strongly correlated with AFP. It is argued whether this is a sole or contributing cause of AFP, or the emotional consequences of suffering with chronic, unrelieved pain. It has been suggested that over 50% of people with AFP have concomitant depression or hypochondria. Furthermore, about 80% of persons with psychogenic facial pain report other chronic pain conditions such as listed in the table.

Lupus headache is a proposed, specific headache disorder in patients suffering from systemic lupus erythematosus (SLE).

Research shows that headache is a symptom commonly described by SLE patients —57% in one meta-analysis, ranging in different studies from 33% to 78%; of which migraine 31.7% and tension-type headache 23.5%. The existence of a special lupus headache is contested, although few high-quality studies are available to form definitive conclusions.

Critics of this concept argue that there are no quality studies showing that headaches in patients with SLE differ from those in the general population. A detailed definition of the term lupus headache is lacking, since the terms "severe" and "persistent" are not quantified. Narcotic analgesics are not recommended for migraines or other common headache types. Other definitions from the IHS do not include responsiveness to treatments as a diagnostic criterion. Migraine patients are typically adult women around age 40, a demographic group in which SLE is also more common.

Atypical facial pain (AFP) is a type of chronic facial pain which does not fulfill any other diagnosis. There is no consensus as to a globally accepted definition, and there is even controversy as to whether the term should be continued to be used. Both the International Headache Society (IHS) and the International Association for the Study of Pain (IASP) have adopted the term persistent idiopathic facial pain (PIFP) to replace AFP. In the 2nd Edition of the International Classification of Headache Disorders (ICHD-2), PIFP is defined as "persistent facial pain that does not have the characteristics of the cranial neuralgias [...] and is not attributed to another disorder." However, the term AFP continues to be used by the World Health Organization's 10th revision of the International Statistical Classification of Diseases and Related Health Problems and remains in general use by clinicians to refer to chronic facial pain that does not meet any diagnostic criteria and does not respond to most treatments.

The main features of AFP are: no objective signs, negative results with all investigations/ tests, no obvious explanation for the cause of the pain, and a poor response to attempted treatments. AFP has been described variably as a medically unexplained symptom, a diagnosis of exclusion, a psychogenic cause of pain (e.g. a manifestation of somatoform disorder), and as a neuropathy. AFP is usually burning and continuous in nature, and may last for many years. Depression and anxiety are often associated with AFP, which are either described as a contributing cause of the pain, or the emotional consequences of suffering with unrelieved, chronic pain. For unknown reasons, AFP is significantly more common in middle aged or elderly people, and in females.

Atypical odontalgia (AO) is very similar in many respects to AFP, with some sources treating them as the same entity, and others describing the former as a sub-type of AFP. Generally, the term AO may be used where the pain is confined to the teeth or gums, and AFP when the pain involves other parts of the face. As with AFP, there is a similar lack of standardization of terms and no consensus regarding a globally accepted definition surrounding AO. Generally definitions of AO state that it is pain with no demonstrable cause which is perceived to be coming from a tooth or multiple teeth, and is not relieved by standard treatments to alleviate dental pain.

Depending upon the exact presentation of atypical facial pain and atypical odontalgia, it could be considered as craniofacial pain or orofacial pain. It has been suggested that, in truth, AFP and AO are umbrella terms for a heterogenous group of misdiagnosed or not yet fully understood conditions, and they are unlikely to each represent a single, discrete condition.

The incidence of RCVS is unknown, but it is believed to be "not uncommon", and likely under-diagnosed. One small, possibly biased study found that the condition was eventually diagnosed in 45% of outpatients with sudden headache, and 46% of outpatients with thunderclap headache.

The average age of onset is 42, but RCVS has been observed in patients aged from 19 months to 70 years. Children are rarely affected. It is more common in females, with a female-to-male ratio of 2.4:1.

Psychogenic pain, also called psychalgia, is physical pain that is caused, increased, or prolonged by mental, emotional, or behavioral factors.

Headache, back pain, or stomach pain are some of the most common types of psychogenic pain. It may occur, rarely, in persons with a mental disorder, but more commonly it accompanies or is induced by social rejection, broken heart, grief, lovesickness, or other such emotional events.

Sufferers are often stigmatized, because both medical professionals and the general public tend to think that pain from psychological source is not "real". However, specialists consider that it is no less actual or hurtful than pain from other sources.

The International Association for the Study of Pain defines pain as "an unpleasant sensory and emotional experience associated with actual or potential tissue damage, "or described in terms of such damage"" (emphasis added). In the note accompanying that definition, the following can be found about pain that happens for psychological reasons:

Many people report pain in the absence of tissue damage or any likely pathophysiological cause; usually this happens for psychological reasons. There is usually no way to distinguish their experience from that due to tissue damage if we take the subjective report. If they regard their experience as pain and if they report it in the same ways as pain caused by tissue damage, it should be accepted as pain.

Medicine refers also to psychogenic pain or psychalgia as a form of chronic pain under the name of "persistent somatoform pain disorder" or "functional pain syndrome". Causes may be linked to stress, unexpressed emotional conflicts, psychosocial problems, or various mental disorders. Some specialists believe that psychogenic chronic pain exists as a protective distraction to keep dangerous repressed emotions such as anger or rage unconscious.

It remains controversial, however, that chronic pain might arise purely from emotional causes. Treatment may include psychotherapy, antidepressants, analgesics, and other remedies that are used for chronic pain in general.