Syphilis is an STI more common among men than women. Syphilis used to be more debilitating and even fatal, but thanks to the rise of antibiotics and safer sex practices, the infection is much rarer today. Untreated, syphilis can enter the bloodstream and affect other parts of the body.
Syphilis actually unfolds in as many as five stages. At some stages, the infection is contagious, at others it is not. Not all people with syphilis experience all five stages.
In the first stage, the only symptom may be the painless sore. If the syphilis advances, though, symptoms can include headache, fatigue, and fever.
The best way to avoid syphilis is to practice safer sex. Condoms are one option, but keep in mind that syphilis can be spread through mouth-to-genital or sometimes mouth-to-mouth contact.
If you think you may have syphilis, see a doctor to be sure. Notify your sexual partner(s), as they would need to be tested for the infection as well.