Primary sore or ulcer at the site of entry of a pathogen; specifically, the typical skin lesion of primary infectious syphilis. In women it is often internal and may go unnoticed. This single red papule (bump), usually occurring about three weeks after infection, and painless regional lymph-node swelling are the major signs of early-stage syphilis. Identification of Treponema pallidum in its fluid makes the diagnosis. The chancre heals in two to six weeks, but syphilis progresses unless treated with penicillin.