The following information may help to address your question:
What are cluster headaches?
are a form of headache notable for their extreme pain and their pattern of occurring in "clusters", usually at the same time(s) of the day for several weeks. The headaches are accompanied by autonomic
symptoms, and some people experience restlessness and agitation.
A cluster headache begins with severe pain strictly on one side of the head, often behind or around one eye. In some people, it may be preceded by a migraine-like "aura." The pain usually peaks over the next 5 to 10 minutes, and then continues at that intensity for up to three hours before going away. Typical attacks may strike up to eight times a day and are relatively short-lived. On average, a cluster period lasts 6 to 12 weeks. Autonomic symptoms may include: conjunctival injection (bloodshot eyes), swelling under or around the eye, excessive tearing of the eyes, drooping of the eyelid, runny nose and/or nasal congestion, and forehead and facial sweating. These symptoms generally occur only during the pain attack and are on the same side as the headache pain.
Cluster headaches usually begin between the ages of 20 and 50, although they can start at any age. Males are more commonly affected than females. Treatment can be divided into acute therapy aimed at stopping symptoms once they have started and preventive therapy aimed at preventing recurrent attacks during the cluster period. 
Last updated: 7/14/2015
What are the signs and symptoms of cluster headaches?
People with cluster headaches describe the pain as piercing and unbearable. The headaches occur in "clusters" usually at the same time of the day and night for several weeks. The symptoms are usually experienced on one side of the head, often behind or around the eye. The nose and the eye on the affected side of the head may also get red, swollen, and runny. Some people will experience nausea; restlessness; changes in blood pressure
and heart rate
; and agitation, or sensitivities to light, sound, or smell. Most affected individuals have one to three cluster headaches a day and two cluster periods a year, separated by periods of freedom from symptoms.
A small group of people develop a chronic form of the disorder, characterized by bouts of cluster headaches that can go on for years with only brief periods (2 weeks or less) of remission.
Last updated: 4/1/2016
What causes cluster headaches?
Scientists aren't sure what causes cluster headaches, although there are currently several theories. The tendency of cluster headaches to occur during the same time(s) from day to day, and more often at night than during the daylight hours, suggests they could be caused by irregularities in the body’s circadian rhythms
, which are controlled by the brain and a family of hormones that regulate the sleep-wake cycle. The development of cluster headaches may additionally be related to the body's release of histamine
(chemical released in the body during an allergic response) or serotonin
(chemical made by nerve cells). It is also possible that a problem in a part of the brain called the hypothalamus
may be involved. 
Alcohol (especially red wine) provokes attacks in more than half of those with cluster headaches, but has no effect once the cluster period ends. Cluster headaches are also strongly associated with cigarette smoking.
Glare, stress, or certain foods may also trigger an attack.
An increased familial risk of these headaches suggests that there may be a genetic cause, though more studies are needed to confirm this suspicion and identify specific genetic changes associated.
Last updated: 4/1/2016
Are cluster headaches related to Horner's syndrome?
Horner's syndrome, a rare condition that affects the nerves to the eye and face, may present during a cluster headache attack. The condition is not present between episodes. However, this fleeting presentation can evolve into persistent Horner's syndrome.
Horner's syndrome can be caused by any interruption in the sympathetic nerve fibers, which start in the part of the brain called the hypothalamus and run to the face. Sympathetic nerve fiber injuries can result from migraine or cluster headaches.
To read more about the association between cluster headaches and Horner's syndrome, you can visit PubMed, a searchable database of medical literature. Information on finding an article and its title, authors, and publishing details is listed here. Some articles are available as a complete document, while information on other studies is available as a summary abstract. To obtain the full article, contact a medical/university library (or your local library for interlibrary loan), or order it online using the following link. Using "cluster headaches AND Horner syndrome" as your search term should locate articles. Click here to view a search.
The National Library of Medicine (NLM) Web site has a page for locating libraries in your area that can provide direct access to these journals (print or online). The Web page also describes how you can get these articles through interlibrary loan and Loansome Doc (an NLM document-ordering service). You can access this page at the following link http://nnlm.gov/members/. You can also contact the NLM toll-free at 888-346-3656 to locate libraries in your area.
Last updated: 3/6/2012
How might cluster headaches be treated?
Treatment does not cure cluster headaches. The goal of treatment is to relieve symptoms. Spontaneous remission may occur, or treatment may be required to prevent headaches.
There are medications available to lessen the pain of a cluster headache and suppress future attacks. Oxygen inhalation and triptan drugs
(such as those used to treat migraine) administered as a tablet, nasal spray, or injection can provide quick relief from acute cluster headache pain. Lidocaine nasal spray, which numbs the nose and nostrils, may also be effective. Ergotamine
and corticosteroids such as prednisone
may be prescribed to break the cluster cycle and then tapered off once headaches end. Verapamil
may be used preventively to decrease the frequency and pain level of attacks. Lithium
, valproic acid
, and topiramate
are sometimes also used preventively.
More detailed information on medications can be found in the treatment
sections of Medscape Reference's article on cluster headache.
Last updated: 11/1/2013
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