Cluster headaches are a type of severe headache that occur in cyclical patterns or clusters. They are characterized by intense, burning pain, usually on one side of the head, often around the eye. These headaches can last from 15 minutes to three hours and may occur multiple times a day during a cluster period, which can last weeks to months. The exact cause of cluster headaches is not fully understood, but they may be related to changes in the body's biological clock or hypothalamus activity. Triggers can include alcohol, smoking, and certain foods. Treatment options include medications for pain relief and preventive therapies.