Despite the fact that we’ve never known more about how to prevent the spread of sexually transmitted infections (STIs), rates of many STIs continue to rise.

While this overall trend is worrying experts, syphilis makes for an especially striking case study. The rates of primary and secondary syphilis (also called P&S syphilis, these are the most infectious stages of the disease) reached a historic low at the turn of the century. In 2000 and 2001, there were 2.1 cases of P&S syphilis per 100,000 people, according to the Centers for Disease Control and Prevention (CDC). But the national reported rate of this illness has climbed nearly every year since 2001, jumping 72.7 percent from 2013 to 2017, when the rate of syphilis reached 9.5 cases per 100,000 people.

To wrap our heads around these ballooning stats, we spoke to a couple of STI experts about why rates of syphilis are rising, who this condition is affecting, what’s being done to solve the issue, and how you can stay safe in the meantime.

What syphilis is and how it spreads

Syphilis is a bacterial sexually transmitted infection caused by the pathogen Treponema pallidum, according to the CDC. It can spread during vaginal, anal, and oral sex if someone makes direct contact with a syphilitic sore known as a chancre. Chancres can appear on or around the genitals or mouth. Also, in what’s called congenital syphilis, a pregnant person can pass the infection to their fetus.

The way syphilis presents and progresses can make it hard to catch without STI screenings, Peter Leone, M.D., M.P.H., adjunct professor at the UNC School of Medicine and adjunct associate professor of epidemiology at the Gillings School of Global Public Health, tells SELF. Read more via SELF