A unilateral headache is a type of headache that occurs on one side of the head. This condition can be associated with various types of headaches, including migraines and cluster headaches. The pain can range from mild to severe and may be accompanied by other symptoms such as nausea or sensitivity to light. The exact cause of unilateral headaches can vary. In the case of migraines, they may be triggered by factors like stress, certain foods, or hormonal changes. Cluster headaches, on the other hand, often occur in cyclical patterns and can be extremely painful, typically affecting one side of the head around the eye area.