It can be caused by a variety of environmental irritants, including chemical fumes, wind, ultraviolet radiation and long-term topical medication; inflammation induced by microbial infection or a metamorphic reaction of the immune system that triggers conjunctival vasodilatation; and physiological or pathological factors that cause pressure on the conjunctival vessels, which can also produce symptoms of conjunctival congestion. Conjunctival congestion is a common manifestation of all types of conjunctivitis. Some conjunctival congestion is also due to other causes.
For example, trauma, high blood pressure, and increased intracranial pressure are common triggers of conjunctival congestion.