I. Acquired syphilis is divided into early syphilis and late syphilis. Early syphilis occurs less than two years after infection and includes stage I syphilis and stage II syphilis, while late syphilis occurs more than two years after infection, i.e. stage III syphilis. Stage I syphilis occurs 3 weeks (between 10 and 30 days) after infection. A hard, painless, round nodule appears at the site of infection. It is flushed and moist at first, and gradually breaks down and erodes, forming an ulcer, known as a stage I syphilis chancre. The main damage is the hard chancre, where the syphilis spirochete first invades and multiplies. The typical chancre is a painless red nodule that is hard and cartilage-like to the touch, with a clean base and a vesicular surface covered with a little exudate or a thin crust, with neat edges. The number of lesions is mostly single, but can be multiple. The lesions tend to occur on the external genitalia. In men, the lesions occur on the foreskin, coronal sulcus, glans or tether of the penis. In homosexual men, the lesions often occur in the anorectal area. In women, it is more likely to occur on the inner part of the labia majora and labia minora, and may also occur on the cervix. The lymph nodes in the groin are enlarged bilaterally, but are not painful. In women, the chancre is usually found on the inner part of the labia minora, or on the cervix. The hard chancre of stage I syphilis contains many syphilis spirochetes and is often accompanied by enlarged local lymph nodes. It is highly contagious. The chancre lasts for 2-6 weeks and then resolves on its own without scarring. However, because of the hidden location of the female chancre and the lack of symptoms, it is often overlooked and increases the chance of transmission. If stage I syphilis is not treated or not treated properly, the spirochete can spread throughout the body via bloodstream and lymph nodes, and then develop into stage II syphilis in a few weeks.