Syphilis is caused by the pale spirochete, the syphilis spirochete, which is a very complex microorganism containing many antigenic substances. Electron microscopically the outermost layer of the syphilis spirochete is the outer membrane, inside the outer membrane is the cytoplasmic membrane, and between the two is the flagellum. After entering the body from intact mucous membranes and abraded skin, syphilis spirochetes invade the nearby lymph nodes after a few hours and spread throughout the body via blood circulation in 2-3 days. After the onset of the disease, which is known as stage 1 syphilis, the external manifestation is a mucocutaneous rash. The specific pathogenesis of syphilis is as follows: After 2-3 weeks of incubation period (called the first incubation period), skin damage (typical damage is hard chancre) occurs after syphilis invades the body. The first stage of syphilis is characterized by mononuclear cell infiltration, with lymphocyte infiltration on the 6th day of infection, reaching a peak on the 13th day, followed by the appearance of macrophages. In this case, syphilis spirochetes are found in the interstitial space of epithelial cells in the sclerosing chancre, as well as in the invaginations of epithelial cells or within the phagocytes, or between fibroblasts, plasma cells, small capillary endothelial cells and in lymphatic vessels and local lymph nodes. As a result of immunization, syphilis spirochetes are rapidly eliminated from the lesion, and after the 24th day of infection, no syphilis spirochetes are detected by immunofluorescence testing. Most of the spirochetes are killed, the hard chancre disappears naturally and enters the asymptomatic latent phase, which is known as stage I latent syphilis. In the past, latent syphilis was mainly detected by serologic tests, but now genetic diagnosis can be applied to detect it quickly and accurately.