DefinitionA cluster headache is one-sided head pain that may involve tearing of the eyes and a stuffy nose. Attacks occur regularly for 1 week to 1 year, separated by long pain-free periods that last at least 1 month, possibly longer.See also:HeadacheMigraine headacheTension headacheAlternative NamesHistamine headache; Headache - histamine; Migrainous neuralgia; Headache - clusterCauses, incidence, and risk factorsCluster headaches are a fairly common form of chronic, repeated headaches. They are more common in men than women. The headaches can occur at any age but are most common in adolescence and middle age. The tend to run in families.Scientists do not know exactly what causes cluster headaches, but they appear to be related to the body's sudden release of histamine or serotonin.The fo