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Cluster headaches are an extremely painful type of headache in which attacks appear in ‘clusters’, or cyclically. During a cluster cycle, excruciatingly severe attacks recur anywhere from 1 to 8 times per day, and cycles can last for weeks or even months.

It’s a rare condition that affects only 0.1 to 0.2% of the population and is 5 to 6 times more common in men than women, the latter of which describe the pain as worse than childbirth.

While treatment is tricky, walking or mobilizing do at least seem to provide temporary relief. Due to the severity of the pain, cluster headaches have been termed ‘suicide headaches’ and are often described as burning or like a hot poker in the eye.

As with most types of headaches, cluster headaches are divided into chronic and episodic. Chronic cluster headaches are defined as either having very brief remissions which last less than 1 month, or having no remissions at all for a period of 1 or more years. Episodic cluster headaches, on the other hand, are separated by periods of remission lasting weeks or even months in which the patient experiences no pain. Less than 20% of cluster headache sufferers have the chronic variety, but those who do are significantly impacted by the disorder.

Cluster headaches are classified as a primary headache disorder, meaning they are not caused by an underlying medical condition, and fall into the group of headache disorders known as trigeminal autonomic cephalalgias (TACs).

Headaches in this category are characterized by moderate to severe unilateral pain over the eye, the temple area, or the forehead and are accompanied by so-called autonomic symptoms, such as redness of the eyes, sensitivity to light, a runny nose, and the secretion of tears.

While scientists have been unable to identify exactly what causes cluster headaches, they are most often linked to disruptions in the body’s biological clock and frequently develop during sleep. Headaches also tend to appear at the same time every day and occur more often in the spring and fall.

Unlike migraine and other types of headaches, food, stress, and hormones are not thought to be triggers, but drinking alcohol and smoking can increase the likelihood of an attack. Even though the underlying cause is unknown, the pain can be explained by the dilation of blood vessels which creates pressure on the trigeminal nerve. The hypothalamus is also believed to be involved, since this is the part of the brain that’s responsible for circadian rhythms.

The onset of cluster headaches usually occurs between the ages of 20 and 40, although misdiagnosis is cited as a real problem and proper diagnosis can therefore take 5 to 7 years. This is because there are a number of primary headache disorders that mimic cluster headaches, such as migraine with prominent autonomic features, paroxysmal hemicrania, and hemicrania continua.

In terms of gender differences, although cluster headaches affect males more than females, the former 2 to 1 ratio seems to have evened out over the years.