Syphilis is a sexually transmitted infection caused by bacteria called Treponema pallidum. There are different stages of syphilis, and each stage has different symptoms. Primary syphilis occurs 2 or 3 weeks after infection, with symptoms of 1 or more small, painless ulcers (chancres) in areas of sexual contact. Because the chancres are painless and go away on their own, many people do not seek treatment. This can lead to secondary syphilis a few weeks or months later. Symptoms of secondary syphilis include flulike symptoms, fever, a widespread rash, and swollen lymph nodes. If still left untreated, these symptoms disappear and a period of latent syphilis follows that can last for several years and during which people may have no symptoms. Symptoms of tertiary syphilis (or late-stage syphilis) can arise, which include serious damage to many organs such as the heart, brain, spinal cord, and bones.