Syphilis, which the bacterium Treponema pallidum causes, is a form of sexually transmitted infection. There are four stages of syphilis. The infection can be serious or cause severe complications without treatment.
Primary syphilis includes the first sign of syphilis, which is typically a small and painless sore near the genitals, anus, or mouth, near the site of infection.
If a person does not seek treatment after noticing these first signs appear, syphilis may progress to the second stage.
According to one 2016 study that appeared in the journal Head and Neck PathologyTrusted Source, around 25 percent of people who have an infection of the Treponema pallidum bacterium will develop secondary syphilis.
At the secondary stage of the disorder, syphilis is still curable with medication. If the person does not work to treat the condition, however, it may progress to further stages, where medical treatment is more difficult or impossible.
The most common sign of secondary syphilis is a rash that does not itch or cause pain. The rash may appear on one part of the body or be more widespread.