Syphilis is a sexually transmitted infection (STI). It's usually spread through sexual contact. But it can also spread to the fetus of a person who has syphilis during pregnancy. The most common symptom is a painless sore on the genitals, rectal area, or mouth. Later symptoms may include rash, hair loss, and flu-like symptoms.
Early symptoms may go away on their own, but the infection is still there and can spread if it isn't treated. Antibiotics can treat syphilis and help prevent serious health problems, like problems with the heart or brain.