150x150px 150x150px 150x150px Positron emission tomography (PET) shows brain areas being activated during pain 150x150px 150x150px 150x150px Voxel-based morphometry (VBM) shows brain area structural differences The cause of<unk>  is unknown.<unk> s were historically described as vascular headaches, with the belief that intense pain was caused by dilation of blood vessels which in turn, was thought to create pressure on the trigeminal nerve. The vascular theory has been called into question and other mechanisms are being considered. The Third Edition of the International Classification of Headache disorders classifies CH as belonging to the trigeminal autonomic cephalalgias. Nerves Two nerves are thought to play an important role in CH: the trigeminal nerve and the facial nerve. Genetics<unk>  may run in some families in an autosomal dominant inheritance pattern. People with a first degree relative with the condition are about 14–48 times more likely to develop it themselves, and around 8 to 10% of persons with CH have a positive family history. Several studies have found a higher number of relatives affected among female. Others have suggested these observations may be due to lower numbers of females in these studies. Possible genetic factors warrant further research, current evidence for genetic inheritance is limited. Genes that are thought to play a role in the disease are the hypocretin/orexin receptor type 2 (HCRTR2), alcohol dehydrogenase 4(ADH4), G protein beta 3 (GNB3), pituitary adenylate cyclase-activating polypeptide type I receptor (ADCYAP1R1), and membrane metalloendopeptidase (MME) genes. Tobacco smoking About 65% of persons with CH are, or have been, tobacco smokers. Stopping smoking does not lead to improvement of the condition and CH also occurs in those who have never smoked (e.g. children); it is thought unlikely that smoking is a cause. People with CH may be predisposed to certain traits, including smoking or other lifestyle habits. Hypothalamus A review suggests that the suprachiasmatic nucleus of the hypothalamus, which is the major biological clock in the human body, may be involved in<unk> s, because CH occurs with diurnal and seasonal rhythmicity. Positron emission tomography (PET) scans indicate the brain areas which are activated during attack only, compared to pain free periods. These pictures show brain areas that are active during pain in yellow/orange color (called "pain matrix"). The area in the center (in all three views) is specifically activated during CH only. The bottom row voxel-based morphometry (VBM) shows structural brain differences between individuals with and without CH; only a portion of the hypothalamus is different.
Cluster headache
Migraine
Lupus headache
Trigeminal neuralgia
Vascular headache
Trigeminal autonomic cephalgia
Tension headache
Medication overuse headache