Syphilis is a contagious, sexually transmitted infectious disease caused by Treponema pallidum. Currently, syphilis is classified into early syphilis—which includes primary-secondary syphilis and latent syphilis lasting less than one year in Anglo-Saxon countries or two years in the United States—and late syphilis, which includes latent syphilis lasting more than one or two years and tertiary syphilis. One of the clinical characteristics of primary-secondary syphilis is its spontaneously regressive course, with a risk of the infection spreading if left untreated. Finally, due to obvious locations (e.g., vaginal, anal, tonsillar), the diagnosis of primary syphilis is often overlooked, leading to a delay in diagnosis and a high risk of transmission to new partners. (R.A.)