Syphilis spreads through unprotected sex with an infected person. It first shows up as a small, painless sore called a chancre on your genitals, rectum, or mouth. If it’s inside your body, you may not notice it. As it worsens, you can get a rash all over your body, even your palms and the soles of your feet. It doesn’t itch. If you don’t treat syphilis, it can damage your heart, brain, and nervous system. You can also spread it to others.