The syphilis spirochete is caused by the invasion of the syphilis spirochete into the human body. After the syphilis spirochete invades the human body, after an incubation period of 2-3 weeks, skin damage occurs, and the typical damage is hard chancre, which is the first stage of syphilis, and after the occurrence of skin damage, the body produces antibodies. From experiments, it is proved that the histological characteristics of the initial stage of syphilis are mononuclear cells, infiltration on the 6th day of infection, that is, lymphocyte infiltration. At this time, syphilis spirochetes are seen in the interstitial epithelial cells in the hard chancre, as well as in the invagination or phagocytosis of epithelial cells, or in fibroblasts, plasma cells, small capillary endothelial cells, and lymphatic vessels and peripheral lymph nodes. The syphilis spirochete is rapidly eliminated from the lesion due to the action of immunity. After the 24th day of infection, the presence of syphilis spirochetes is not detected by immunofluorescence testing, and the spirochetes are mostly killed and enter the asymptomatic latent phase, which is stage I latent syphilis.