Cluster headaches affect one side of the head (unilateral) and may involve tearing of the eyes and a stuffy nose. The headaches occur repeatedly every day at the same time for several weeks and then go away.

Cluster headaches are a fairly common form of chronic, recurrent headache. Unlike migraines, they affect men more often than women. They can affect people of any age but are most common between adolescence and middle age. There does not seem to be a pattern among families in the development of cluster headaches.

A cluster headache begins as a severe, sudden headache. No specific cause has been found for the disorder, but it appears to be related to a sudden release of histamine or serotonin by body tissues.

The onset is sudden, and it happens most commonly during the dreaming (REM) phase of sleep. Cluster headaches may occur daily for months, alternating with periods without headaches (episodic), or they can recur for a year or more without stopping (chronic). A person may experience alternating chronic and episodic phases.

Some people who experience cluster headaches are heavy smokers. Alcohol use may trigger attacks. Glare, stress, or certain foods may trigger an attack.

• Swelling under or around the eyes (usually one eye, on the same side as the head pain)
• Excessive tears (on the affected side)
• Red eye (on the affected side)
• Rhinorrhea (runny nose) or nasal congestion (typically occurs on only one side of the nose, the same side as the head pain)
• Red, flushed face
• Headache
  • Begins suddenly
  • Commonly begins 2 to 3 hours after falling asleep
  • Steady, sharp pain
  • Burning or boring pain
  • Characteristically occurs on one side of the head
  • May occur in and around one eye
  • May involve one side of the face from neck to temples
  • Pain quickly gets worse, peaking within 5 to 10 minutes
  • Peak pain may last one-half to 2 hours

Cluster headaches may be diagnosed by your health care provider based on the symptoms and a physical examination. Tests may be required to rule out other causes of the symptoms. Examination usually shows no specific neurologic effects except for Horner's syndrome (one-sided eyelid drooping or small pupil) during an attack that is not present between episodes. This can evolve into persistent Horner's syndrome.

An MRI of the head may be done to rule out other pathology.