Cluster headaches are recurring headaches whose attacks last 15 minutes to three hours and several times a day for weeks or even months and years. The pain arrives with little, if any, warning and it has been described as the most severe and intense of any headache type, with severe pain on one side of the head, usually in and around the eye. The pain is so intense that sufferers have considered suicide during attacks. It is associated with tearing, red eye, stuffy nose, facial sweating or other changes in the eye. Clusters often occur during spring or autumn and thus are often incorrectly associated with allergies.
Cluster headaches affect about 1% of the population, usually men between the ages of 20 and 45 (about 80% of the victims are men). Around 20% of patients seem not to respond to any treatments; surgery may be recommended. Triggers include alcohol, smoking, sleep deprivation, excessive exercise, volatile chemicals and changes in barometric pressure.