There are herpes simplex viruses of type I and type II. Most herpes simplex virus keratitis is caused by herpes simplex virus type I; type II infections are in the genitalia and occasionally in the eyes. Herpes simplex virus type I causes both primary and recurrent infections. The vast majority of adults have been exposed to herpes simplex virus and most are asymptomatic. After primary infection, the herpes simplex virus is latent in the trigeminal ganglion. When the body’s resistance decreases or is stimulated, the latent virus activates and travels retrogradely along the nerve axons to the sensory nerve endings, causing recurrent infection and disease. Therefore, it is transmitted after human contact. Herpes simplex virus type I is transmitted by adults kissing their children or by close contact between children, by kissing between adolescents and adults, and by occasional sexual intercourse. Herpes simplex virus is highly contagious to people, and most people are infected, with a seropositivity rate of 90% and molecular biology tests reaching 55% to 94% of people being infected. type II is mainly sexual contact, and can also cause eye infection due to sexual intercourse, and newborns can be infected through the birth canal.