Syphilis is an STI that can cause long-term complications and/or death if not treated correctly. It's a most common in people who are sexually active. Unprotected sex is usually how people get the infection, particularly if you have multiple sexual partners. Syphilis is common in men who have sex with other men.
It is estimated that people with syphilis are three to five times more likely to catch HIV.
Last updated August 12, 2016