Arguably worse than contracting a sexually transmitted infection (STI): passing it on to someone else.

The best way to prevent that from happening is to get screened for STIs. Since most of them are asymptomatic-meaning there’s nothing you’ll see or feel that will tip you off to your infection-screening is the only way to know for sure you’re STI-free. So how often should you get screened?

Scenario 1: Once a Year

If you’re sexually active and not in a monogamous relationship, you should be screened at least once a year, according to the CDC. But that’s the minimum. There are many scenarios that demand more frequent screening.

Scenario 2: Every Time You Have a New Sexual Partner

“Whenever you have sex with a new partner, after that is a good time to consider being screened,” says Christine Johnston, MD, an associate professor of infectious disease at the University of Washington. She says that’s doubly true if you’re engaged in unprotected sex-including unprotected oral or anal sex.

Scenario 3: If You Have Multiple Partners

If you're engaged with multiple partners, Johnston recommends going in for an STI screening every three months. And that recommendation is in line with the CDC’s screening guidelines.

But let’s say you’re going out every weekend and spending the night with a new partner. Shouldn’t you get screened a lot more than once every three months? You’ve got a point, Khalil Ghanem, MD, PhD, an associate professor of medicine at Johns Hopkins University School of Medicine, says. More-frequent screening would be the safest route-and the only way to ensure you’re not putting your partners at risk.

“I’ve had high-risk patients that I’ve screened every month,” he says. “But that’s tough.”

By tough, he means expensive, plus time- and resource-consuming. If you’re having unprotected sex with new partners all the time, your odds of contracting and spreading around an STI are dangerously high. You need to wear some protection if you’re going to play the field that way.

Deciding the Right Testing Schedule for You

Different types of sex demand different screening procedures. If you’re engaged in unprotected oral and vaginal sex on a regular basis and with unfamiliar partners, you may need a blood test, a pee test, and both urethral and throat swabs, Ghanem explains. If you’re also engaged in anal sex, you can add anal swabs to the list of screening measures.

Again, going through all this after every sexual encounter isn’t reasonable-both for you and for America’s health care system. So use some protection.