Sign in
What Are They

What are they?

Cluster headaches are exceptionally severe headaches that occur for no known cause. Cluster headaches are rarer than migraines, affecting only 69 out of every 100,000 people (less than one percent). Men are six times more likely to develop cluster headaches than women.

Cluster headaches can strike at any age, but usually develop in men between the ages of twenty and fifty. Women are more likely to develop severe cluster headaches after age fifty.

Cluster headaches are excruciating unilateral headaches of extreme intensity. The duration of the common attack ranges from as short as 15 minutes to three hours or more. The onset of an attack is rapid, and most often without the preliminary signs that are characteristic of a migraine. However, some sufferers report preliminary sensations of pain in the general area of attack, often referred to as "shadows", that may warn them an attack is imminent. Though the headaches are almost exclusively unilateral, there are some documented as cases of "side-shifting" between cluster periods, or, even rarer, simultaneously (within the same cluster period) bilateral headache

Cluster headaches are so named because attacks "cluster" in four to eight week cycles. Frequency of attacks vary among individuals. Some people experience as many as six severe headaches a day, while others report only one cluster headache a week. On average, cluster headache sufferers can expect one to two severe headaches a day for the duration of the cycle.

Often the severe headaches that characterize cluster headaches can be predicted ahead of time. In 85 percent of cases cluster headaches will occur at the same time of day for an entire cycle.

The Pain

The pain of cluster headaches is markedly greater than in other headache conditions, including severe migraines; experts have suggested that it may be the most painful condition known to medical science. Female patients have reported it as being more severe than childbirth. Dr. Peter Goadsby, Professor of Clinical Neurology at University College London, a leading researcher on the condition has commented:

"Cluster headache is probably the worst pain that humans experience. I know that’s quite a strong remark to make, but if you ask a cluster headache patient if they’ve had a worse experience, they’ll universally say they haven't. Women with cluster headache will tell you that an attack is worse than giving birth. So you can imagine that these people give birth without anesthetic once or twice a day, for six, eight, or ten weeks at a time, and then have a break. It's just awful."

It is a headache, in that the pain is in the head, but that is really where the similarity ends. The name itself leads to confusion, as people immediately think of it as something that can be cured by taking a pill, or by thinking of it as a migraine. As one who has had both conditions, clusters are nothing like migraine.

It is stated by neurologists to be the most severe pain experienced by human beings - female sufferers say that it is more painful than childbirth. Imagine that for several weeks at a time.

Or imagine an ice-cream headache in your temple or behind your eye that is about 5 times worse, and lasts up to 3 hours.

Another analogy is being hit with a baseball bat on the side of the head - take that instant of impact but extend it to be continuous for 30, 60 90 minutes. Try 3 hours. Imagine how physically and emotionally exhausting dealing with that kind of pain in your head would be, along with the fear that it might not stop.

Cluster Headache Symptoms

Cluster headaches start suddenly, with little warning. Within two to fifteen minutes of symptom onset, the pain becomes excruciatingly severe. Cluster headaches usually start around or above the eye or temple.

Cluster headaches cause severe unilateral pain, meaning the headache occurs on only one side of the head. In the majority of cases cluster headaches always occur on the same side of the head. In fifteen percent of cases cluster headaches may switch from one side of the head to the other.

Because it is so rare, sufferers often feel isolated, especially through misunderstanding by those who do not fully appreciate its effects. Cluster headache, nicknamed "suicide headache", is a neurological condition that involves, as its most prominent feature, an immense degree of pain. "Cluster" refers to the tendency of these headaches to occur periodically, with active periods interrupted by spontaneous remissions. The underlying cause is currently unknown.

It is frequently accompanied by some or all of:

The intense pain is caused by the dilation of blood vessels which creates pressure on the trigeminal nerve. While this process is the immediate cause of the pain, the underlying cause is not fully understood.

The attacks are relatively short (1-3 hours), with a very rapid onset. They tend to occur several times a day, most frequently waking the patient in the early hours. There are two types of the condition, episodic and chronic. In the episodic form, the attacks occur in a bout lasting several weeks (4 – 12), after which they disappear for around a month. This is where the name cluster headache comes from. Chronic sufferers do not get this relief, and their attacks can continue daily for many years (25 or more is not unknown).

A curiosity of C.H. is that both the individual attacks and the clusters themselves can have an almost metronomic regularity - attacks starting at a precise time of day is typical

How is a sufferer affected?

This will vary enormously, and, surprisingly, you will almost certainly never witness a full-blown attack. Seeing someone in that state can be quite terrifying. Sufferers are reluctant to allow anyone else to see them at that point, for three main reasons: first, with family and friends, it is simply to avoid them having to see something which, as they are powerless to help, is very upsetting; second, no-one is keen to be seen in a state where they will scream, cry, pace, hit their head repeatedly and generally be uncontrollable - dignity does matter; and three, coping with the attack is wearing in the extreme, and having to cope with other people around is just not possible for most.

In addition, the cumulative effects of repeated attacks, and the medications used, can lead to tiredness, irritability, and an occasional loss of temper (particularly when it is suggested that things can't possibly be that bad). Depression is quite common. Some individuals lose their jobs, and even partners and homes, as a result of C.H. That said, because having to cope is part of the nature of the condition, most sufferers will "get along" - they have to be quite strong to survive.

Most can be helped by medication, but, because the cause of the illness is unknown, there is no cure. Those on medication take (generally large quantities of) pain-killing and preventative or abortive drugs. These often mask or reduce the symptoms, but never remove them. Sometimes, they simply don't work at all. And what might work for one bout might have no effect the next time around.

It should be noted here that GPs are often poorly informed about C.H., and misdiagnosis is very common. Some GPs are reluctant to prescribe certain drugs, even when they are known to be effective.

What triggers cluster headache?

Alcohol is one well known trigger of cluster headache, often bringing on the pain within an hour of drinking. If you have cluster headache you should not drink any alcohol during a cluster period. Once the bout is over you will be to drink alcohol again.

A significant number of people find that strong smelling substances such as petrol, paint fumes, perfume, bleach or solvents can trigger an attack. During an episode of cluster headaches you should try to avoid these things.

Some people find exercise or becoming over heated will bring on an attack, so again avoiding these is the best advice during a bout.

Research has showed that heavy smokers are at an increased risk of developing chronic cluster headache so giving up smoking or cutting down is worth considering.


What can you do to help?

When an attack hits, nothing. The best thing is to stay well away. Conversation is extremely difficult for them, because all their energy and concentration is consumed by trying to bear the agony they are going through. Afterwards, a quiet word is probably a good idea. You may find the sufferer will talk about what he goes through if you ask - he may appreciate the opportunity to explain. Sympathy will be appreciated.

Things to avoid saying/doing

Most sufferers are happy to discuss how things affect them, and how you can best help them, but you will find your conversations very short if you say any of the following:

  "I had one of those once" - no-one ever has one cluster headache
  "My aunt gets migraines too" - migraine is nothing like cluster headaches
  "Can't you just take a tablet and lie down?" - no is the answer, sufferers cannot lie down during an attack, and tablets do not touch cluster headaches.
  "Just pull yourself together and work through it" - suggest that, and step back several paces!

This is not rudeness, but simply the result of experience. Sufferers know that sometimes it is simply better to ignore remarks such as these and leave the person in ignorance. If you have read this far, though, that probably doesn't apply to you!

What causes it?

The cause of the disease is currently unknown. Biochemical, hormonal, and vascular changes induce cluster headaches, but why these changes occur remains unclear. Episodic cluster headaches seem to be linked to changes in day length, possibly signaling a connection to the so-called biological clock. Alcohol, tobacco, histamine, or stress can trigger cluster headaches. Decreased blood oxygen levels (hypoxemia) can also act as a trigger, particularly during the night when an individual is sleeping. Interestingly, the triggers do not cause cluster headaches during remission periods.


Among the most widely accepted theories is that cluster headaches are due to an abnormality in the hypothalamus; Dr Goadsby, an Australian specialist and the leader in the disease has developed this theory. This can explain why cluster headaches frequently strike around the same time each day, and during a particular season, since one of the functions the hypothalamus performs is regulation of the biological clock. Metabolic abnormalities have also been reported in patients.

The hypothalamus is responsive to light—daylength and photoperiod; olfactory stimuli, including sex steroids and corticosteroids; neurally transmitted information arising in particular from the heart, the stomach, and the reproductive system; autonomic inputs; blood-borne stimuli, including leptin, ghrelin, angiotensin, insulin, pituitary hormones, cytokines, blood plasma concentrations of glucose and osmolarity, etc.; and stress. These particular sensitivities may underlay the causes, triggers, and methods of treatment of cluster headache.

In both cluster and migraine headaches blood vessels dilate, but in cluster headaches only the blood vessels behind the eyes pulsate. What causes these events and how they relate to cluster headaches are still unclear:


There is a genetic component to cluster headaches, although no single gene has been identified as the cause. First-degree relatives of sufferers are more likely to have the condition than the population at large. However, genetics appears to play a much smaller role in cluster headache than in some other types of headaches.

Other Factors

Nitric Oxide. Nitric oxide is a small molecular messenger that activates nerve pathways in the brain, muscles, or elsewhere. It may contribute to major primary headaches (tension-type, cluster, and migraines) by specifically triggering inflammation and over activity in the trigeminal nerves. (This is a major nerve pathway that runs from the brain stem to the head and face.) However, other factors must be present that make cluster headache patients susceptible to the actions of nitric oxide.

Immune Abnormalities. Researchers are also investigating whether over-production of certain immune factors called cytokines may contribute to cluster headaches. Cytokines, such as interleukins, are known to cause inflammation and injury in high amounts. To date, however, there is no evidence that they play any role.

Abnormalities in the Sympathetic Nervous System. Some evidence suggests that abnormalities in the sympathetic (also called autonomic) nervous system may contribute to cluster headaches. This system regulates non-voluntary muscle actions in the body, such as in the heart and blood vessels.

Click here to download a PDF of some of this information to print and hand to friends and relatives.

Clinical Description

Cluster headaches. Cluster headaches, named for their repeated occurrence over weeks or months at roughly the same time of day or night in clusters, begin as a minor pain around one eye, eventually spreading to that side of the face. The pain quickly intensifies, compelling the victim to pace the floor or rock in a chair. "You can't lie down, you're fidgety," explains a cluster patient. "The pain is unbearable." Other symptoms include a stuffed and runny nose and a droopy eyelid over a red and tearing eye.

This graphic illustrates the Trigeminal Nerve.  This nerve has three branches, one which goes to the forehead and eye, one which goes to the cheek and one which goes to the lower face and jaw.   During a cluster headache, the trigeminal nerve is activated, causing pain along one or more of it's three branches, usually along the one leading to the eye and forehead.  This accounts for the centering of the pain of CH around the eye.

Cluster headaches last between 30 and 45 minutes. But the relief people feel at the end of an attack is usually mixed with dread as they await a recurrence. Clusters may mysteriously disappear for months or years. Many people have cluster bouts during the spring and fall. At their worst, chronic cluster headaches can last continuously for years.

Cluster attacks can strike at any age but usually start between the ages of 20 and 40. Unlike migraine, cluster headaches are more common in men.
Studies of cluster patients show that they are likely to have hazel eyes and that they tend to be heavy smokers and drinkers. Paradoxically, both nicotine, which constricts arteries, and alcohol, which dilates them, trigger cluster headaches. The exact connection between these substances and cluster attacks is not known.
Despite a cluster headache's distinguishing characteristics, its relative infrequency and similarity to such disorders as sinusitis can lead to misdiagnosis. Some cluster patients have had tooth extractions, sinus surgery, or psychiatric treatment in futile efforts to cure their pain.

Other research studies have turned up several clues as to the cause of cluster headache, but no answers. One clue is found in the thermograms of untreated cluster patients, which show a "cold spot" of reduced blood flow above the eye. The cause of cluster headaches is unknown. They may be genetic, since people whose parents or siblings have cluster headaches are at more risk for developing them.

Cluster headaches may be caused by a problem in an area of the brain called the hypothalamus. This area of the brain seems to be more active in people who have cluster headaches. The hypothalamus is a region of the brain that regulates sleep cycles, body temperature, pituitary gland activity, and other autonomic nervous system functions. When the hypothalamus malfunctions, thyroid problems, cluster headaches, and sleeping, eating, or reproductive problems may result.

The sudden start and brief duration of cluster headaches can make them difficult to treat; however, research scientists have identified several effective drugs for these headaches:

Another option that works for some cluster patients is rapid inhalation of pure oxygen through a mask for 5 to 15 minutes. The oxygen seems to ease the pain of cluster headache by reducing blood flow to the brain. which in turn causes the brain to constrict the blood vessels that are iritating the Trigeminal nerve.

In chronic cases of cluster headache, certain facial nerves may be surgically cut or destroyed to provide relief. These procedures have had limited success. Some cluster patients have had facial nerves cut only to have them regenerate years later.

Mayo Foundation of Medical Education and Research. (2003). Cluster headaches.
Beers, M.H. (ed). Cluster headaches. The Merck Manual of Medical Information, 2nd Home Edition. Merck Research Laboratories, NJ, 2003.
National Library of Medicine. (updated 2002). Cluster headaches. MedlinePlus Medical Encyclopedia.
National Library of Medicine. (updated 2002). Horner's syndrome. MedlinePlus Medical Encyclopedia.