Syphilis is a sexually transmitted infection (STI) caused by the bacteria Treponema pallidum. If it's not treated by a doctor, it can get worse over time and cause serious health problems.

The infection can be active at times and not active at other times. When the infection is active, you have symptoms. When it's not active, you don't have symptoms, even though you still have syphilis. But even when you don't have symptoms, you can pass syphilis to others.

You don't have to have sexual intercourse to get syphilis. Just being in close contact with an infected person's genitals, mouth, or rectum is enough to expose you to the infection.