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Cluster headaches

What are cluster headaches?

Cluster headaches usually happen up to three times a day, every day, and for weeks or months. The pain is often behind the eye on one side of the head and is more painful than migraine or other headaches.

Cluster headaches fall into two categories: episodic and long-term (chronic).

A person with episodic cluster headaches may experience a month or longer without headaches before they return.

With chronic cluster headaches, there may be a gap of less than a month between headache periods, or no gap.

Cluster headaches are relatively rare, affecting around one in 1,000 people in the UK. Cluster headaches are more common among smokers and are also more common in men.

What causes cluster headaches?

The true biochemical cause of cluster headaches is unknown. However the headaches occur when a nerve pathway in the base of the brain (the trigeminal-autonomic reflex pathway) is activated. The trigeminal nerve is the main nerve of the face responsible for sensations, such as heat or pain.

Trigeminal Nerve

When activated the trigeminal nerve causes the eye pain associated with cluster headaches. The trigeminal nerve also stimulates another group of nerves that causes the eye tearing and redness, nasal congestion and discharge associated with cluster attacks.

The activation of the trigeminal nerve appears to come from a deeper part of the brain called the hypothalamus. The hypothalamus is home to our ‘internal biologic clock’, which regulates our sleep and wake cycles on a 24-hour schedule. Imaging studies have shown activation or stimulation of the hypothalamus during a cluster attack.

Cluster headaches are not caused by an underlying brain condition such as a tumour or aneurysm.

What triggers cluster headaches?

The season is the most common trigger for cluster headaches, which often occur in the spring or autumn. Due to their seasonal nature, cluster headaches are often mistakenly associated with allergies or business stress. The seasonal nature of cluster headaches most likely results from stimulation or activation of the hypothalamus (see above).

Cluster headaches are also common in people who smoke and drink alcohol frequently. During a cluster period the person is more sensitive to the action of alcohol and nicotine, and minimal amounts of alcohol can trigger the headaches. During headache-free periods the person can consume alcohol without provoking a headache.

What are the symptoms of a cluster headache?

Cluster headaches generally reach their full force within five or 10 minutes after onset. The attacks are usually very similar, varying only slightly from one attack to another.

  • Type of pain: The pain of cluster headache is almost always one-sided, and during a headache period, the pain remains on the same side. When a new headache period starts, it rarely occurs on the opposite side.
  • Severity/intensity of pain: The pain of a cluster headache is generally very intense and severe and is often described as having a burning or piercing quality. It may be throbbing or constant. The pain is so intense that most people having a cluster headache cannot sit still and will often pace during an attack.
  • Location of pain: The pain is located behind one eye or in the eye region, without changing sides. It may radiate to the forehead, temple, nose, cheek or upper gum on the affected side. The scalp may be tender, and the pulsing in the arteries often can be felt.
  • Duration of pain: The pain of a cluster headache lasts a short time, generally 30 to 90 minutes. However it can last from 15 minutes to three hours. The headache will disappear only to recur later that day. Typically, in between attacks, people with cluster headaches are headache free.
  • Frequency of headaches: Most people get one to three headaches per day during a cluster period - the time when a person having a cluster headache is experiencing daily attacks. They occur very regularly, generally at the same time each day, and have been called ‘alarm clock headaches’ because they often awaken the person at the same time during the night.

Cluster headaches are not typically associated with nausea or vomiting. It is possible for someone with cluster headaches to also have migraines.

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