Have unprotected sex (do not use condoms or do not use them correctly). This risk is especially high among men who have sex with other men (MSM).
Have multiple sex partners, particularly if you live in an area of the country where syphilis is more common.
Have a sex partner who has syphilis.
Have sex with a partner who has multiple sex partners.
Exchange sex for drugs or money.
Have human immunodeficiency virus (HIV) infection and engage in any of the behaviors listed above.
Syphilis is contagious whenever an open sore or skin rash is present. The risk of being infected with syphilis from a single sexual encounter with an infected partner is approximately 3% to 10%.4
Infection with syphilis also increases a person's risk of being infected with HIV. Syphilis causes open sores on the genitals that allow the HIV infection to enter the body easily. Syphilis is in general more common in people who are also infected with HIV.