Cluster headaches are a series of very painful headaches of short duration that occur every day for weeks or months. They come at the same time each year, mostly in the spring or fall. This often makes people believe that cluster headaches occur as a fallout of allergy or stress.

Though the exact cause or etiology of cluster headaches is not yet known, certain theories regarding its cause are being put forward.

Cluster headaches are primary headaches and have been categorized as vascular headaches. The intense headache pain is due to the dilatation of the blood vessels, which then press on the trigeminal nerve. Though this causes the pain, why this pain and the cluster headache symptoms occur is still unknown.

Cluster headaches are classified as primary headaches and very rare occurring in 0.1% of the population (one in a thousand people).

Around 25% of these patients will never have another attack. Fifteen to 20 % of patients will develop chronic cluster headaches. However, this condition often resolves in approximately 15 years.

Cluster headache causes

Experts still don’t know much about cluster headaches and what causes them. Cluster headache is a type of trigeminal autonomic cephalgia (headache), which involves the hypothalamus, a part of the brain belonging to the autonomic nervous system, and also involves the trigeminal nerve. 

Though the cause is not known, certain theories are being put forward.

The hypothalamus theory

Among the most popular theories is one, which propagates the cause as an abnormality in the hypothalamus, an area of the brain, which is situated deep in the center of the brain and controls body temperature, hunger, and thirst.

Research has established that during a cluster headache attack there is increased activity in the hypothalamus.

Furthermore, people who have cluster headaches often have unusual levels of melatonin and cortisol during an attack. Melatonin and cortisol are hormones that play a major role in regulating your circadian rhythms and the quality of sleep. 

It is also possible that the hypothalamus releases certain chemicals that cause blood vessels to dilate, leading to more blood flow to the brain. 

The fact that cluster headaches occur at the same time of the day or night and year suggests that the biological clock, which is regulated by the hypothalamus is involved. PET studies done during the pain period have indicated increased activity in the hypothalamus.

What is the biological clock? It is the body’s circadian rhythm, which is a natural, internal process that regulates the sleep-wake cycle and repeats about every 24 hours.

It is believed that due to one-sided activation of the hypothalamus, there is a release of certain hormones and brain chemicals cyclically, which irritate the trigeminal ganglion and induces pain. The trigeminal nerve is the main nerve responsible for pain and heat sensations in the face.

The stimulation of the trigeminal nerve also results in the activation of other nerves, which causes other symptoms of cluster headaches such as increased lacrimation, nasal discharge, and nasal blockage.

The genetic theory

Evidence also exists that points towards the genetic factor playing a role in causing cluster headaches. However, the type or the number of genes involved is not yet identified.

Immediate relatives (parent, sibling, or child) of cluster headache sufferers are more likely to suffer from this condition than other people are.

Cluster headache trigger factors

  • Unlike tension headaches and migraines, which can be triggered by foods, hormonal changes, or stress, there are no definite factors that trigger a cluster headache. However, certain factors can trigger an attack during the cluster period.
  • Smoking and alcohol do increase the pain of cluster headaches during the cluster period and hence sufferers do tend to avoid these substances. However, during the remission period, these substances do not trigger a cluster attack.
  • Certain drugs such as nitroglycerine can trigger a cluster headache because it causes vasodilatation.
  • A particular season such as winter or summer or fall or spring can also trigger a cluster headache and this season varies from person to person. In northern countries, the frequency of the attacks tends to be more during the fall and spring.
  • Extreme changes in temperature or a sudden rise in body temperature or exercising in hot weather may also trigger attacks.

Cluster headache risk factors

Certain factors do put you at risk of developing a cluster headache.

  • Gender. Being male increases your risk because cluster headaches are three times more common in males than females.
  • Age: Though cluster headaches can develop at any age, its onset is most common in the late twenties or thirties.
  • Family history: A genetic trait is believed to be a reason for cluster headaches and immediate relatives of a cluster headache sufferer are more prone to develop this condition.

It can take a very long time to diagnose cluster headaches, up to 5 years or more. Being rare, it is often diagnosed when other causes of headaches have been ruled out after a series of investigations. The first and most common differential diagnosis is migraine.

The best way to improve diagnosis and management chances is by consulting an interprofessional healthcare team dedicated to treating headaches, who will also advise ways to prevent future cluster attacks.