Sudden congestion of the eyes may be related to non-disease factors, disease factors, the former includes individual or environmental factors; the latter includes non-infectious or infectious diseases, etc. 1. Non-disease factors (1) Individual factors: When using the eyes for a long time, or when the body is inverted for a long time, it will lead to the manifestation of bloodshot eyes. (2) Environmental factors: physical factors such as heat radiation and mosquito bites may also lead to eye congestion. 2. Disease factors (1) Non-infectious diseases: keratitis, corneal ulcers, etc. lead to congestion of blood vessels around the corneal limbus; eyelid congestion caused by cavernous sinus thrombosis, sinus tumor compression, etc.; acute angle-closure glaucoma, etc. (2) Infectious diseases: including conjunctival congestion caused by bacterial conjunctivitis, viral conjunctivitis, immune conjunctivitis, etc.; ciliary congestion caused by bacterial keratitis, etc.; and mixed conjunctival congestion and ciliary congestion. It is recommended that people with sudden eye congestion should consult a doctor promptly after excluding non-disease factors, and standardized treatment should be carried out after clarifying the cause of the disease.