What type of headache is characterized by unilateral, severe periorbital pain with tearing and conjunctival erythema?

The type of headache characterized by unilateral, severe periorbital pain with accompanying symptoms such as tearing and conjunctival erythema is indeed a cluster headache. Cluster headaches are known for their distinctive symptoms, which often occur in episodes or "clusters." These headaches typically present as very intense, sharp pain around or behind one eye, and they can be associated with autonomic signs such as nasal congestion, rhinorrhea, and particularly, lacrimation (tearing) as well as conjunctival injection (erythema of the conjunctiva).

The unilateral nature of the pain and the specific location—around the eye—are key features that help differentiate cluster headaches from other headache types. Unlike migraines, which can cause unilateral or bilateral pain with photophobia and aura symptoms, cluster headaches present with clearly defined one-sided pain that is often described as "like a hot poker in the eye."

In contrast to tension headaches, which are typically bilateral and characterized by a dull, aching pain and a tightness in the head or neck rather than the severe pain associated with cluster headaches, and thunderclap headaches, which are sudden, severe headaches that reach peak intensity within minutes and may indicate serious underlying conditions like subarachnoid hemorrhage, cluster headaches