Risk factors are certain elements that increase the likelihood of a person developing a disease or condition. However, not everyone with risk factors will develop syphilis. Likewise, some people who have no risk factors develop the disease. Some risk factors associated with syphilis include:

• Age. Syphilis is most common among sexually active young people, with most cases occurring among men ages 35 to 39 and women ages 20 to 24.
  
  
• Sexual activity. People who have unprotected sex, have multiple sex partners or high-risk or infected sex partners are at greater risk.
  
  
• HIV infection. People with HIV are at greater risk of developing syphilis.
  
  
• Location. Approximately 79 percent of counties in the United States reported no cases of primary or secondary syphilis to the Centers for Disease Control and Prevention (CDC) in 2004. According to the CDC, most of the counties in the United States with primary or secondary syphilis were in the South. People who have any risk factors for sexual activity listed above and who live in areas with reported cases of syphilis are at greater risk.