Syphilis is a sexually transmitted infection caused by the bacterium Treponema pallidum. It often starts with a painless sore, known as a chancre, at the site of infection. If left untreated, syphilis can progress through different stages, leading to serious health issues affecting the heart, brain, and other organs. The infection is primarily spread through sexual contact, but it can also be transmitted from an infected mother to her baby during pregnancy, resulting in congenital syphilis. Early diagnosis and treatment with antibiotics, usually penicillin, can effectively cure syphilis and prevent complications. Regular testing is important for sexually active individuals.