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How is syphilis usually transmitted between people?

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Scanning electron micrograph of Treponema pallidum, the spirochete bacterium that is the causative agent of syphilis. — syphilis Scanning electron micrograph of *Treponema pallidum*, the spirochete bacterium that is the causative agent of syphilis.

Syphilis is primarily a sexually transmitted disease, with sexual intercourse being the most common method of transmission. Because the causative bacterium, Treponema pallidum, requires a moist environment to survive, continuous moisture is necessary for the microorganism to transfer from one person to another.1

During the primary and secondary stages of the disease, the infection can be easily passed to others through direct contact with open sores or lesions. While sexual contact is the standard route, the disease can occasionally be acquired through direct nonsexual contact with an infected person.21

Additionally, syphilis can be transmitted from an infected mother to her unborn fetus during pregnancy. This can lead to serious health complications for the infant, though timely treatment with penicillin can effectively prevent this transmission.123

It is important to note that a related group of infections known as nonvenereal syphilis (or treponematosis) is not spread through sexual contact but is instead transmitted via direct contact, typically among children and young adults in regions with crowded conditions and poor health care.12