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If only sex were all fun and games. Even though it can result in many nice things—closeness, orgasms—it can also lead to sexually transmitted diseases. Although you shouldn’t feel ashamed if you contract one, ignorance is absolutely not bliss; some untreated STDs can lead to complications like infertility.

“Every person needs to be tested,” Edward W. Hook III, M.D., professor of medicine, epidemiology, and microbiology at the University of Alabama, tells SELF. “The question about how often people need to be tested for sexually transmitted infections once they’ve been tested the first time is a function of a number of things, like their number of partners, and their partners’ number of partners.”

What STDs should you be tested for? It can be a little tricky, but here are the basics. The two biggies are chlamydia and gonorrhea. Chlamydia is the most commonly reported STD in the United States, and gonorrhea is also incredibly common. What’s worse, they can both be asymptomatic, are both on the rise, and when left untreated, both can lead to pelvic inflammatory disease, which can cause infertility.

Ironically, doctors often don’t test for the two most common STDs—herpes and HPV (they’re reported less often than chlamydia because people often don’t realize they have them). The reason is just that: They’re so damn common that sometimes it’s not even worth finding out. Since 67 percent of the global population has HSV-1, the kind of herpes most likely to cause cold sores, and one out of every six Americans between 14 and 49 has HSV-2, the type that usually causes genital herpes, your doctor likely won’t test for them unless you specifically ask or have symptoms. Doctors don’t start screening for HPV, which can cause cervical cancer, until you turn 30, preferring to rely on routine Pap smears to detect signs of cervical cancer before then.

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When it comes to HIV, everyone between the ages of 13 and 64 should get tested at least once, the Centers for Disease Control and Prevention recommends. Beyond that, if you have risk factors, like having recently had sex with someone whose sexual history you don’t know, or having more than one sex partner since your last test, you should get an HIV test at least annually. Here’s a full list of potential risk factors.

If you’re experiencing any strange itching, burning, or other worrisome symptoms down below, you should see a doctor to figure out what’s up. But even if you’re symptom free, you should know how often you need to get tested (and then actually do it). It’s not always so clear—and that’s why we put together this handy guide to help you know when to go, based on what’s going on in your love life.

This is how often you need to get tested if…

...you’re in a dry spell but have had sex within the past year:

If you’re engaging in sexual activity at least once a year and you’re between the ages 21 and 25, you should be getting tested for chlamydia annually. “The prevalence of chlamydia up until age 25 is so high that it’s important to test for it,” board-certified ob/gyn Antonio Pizarro, M.D., tells SELF.

Since gonorrhea is also a common STD in people of that age range, your doctor will likely want to check you out for that as well, Hook explains. At this appointment, you and your doctor can discuss your sexual history and which other STD tests you might need.

If you're over 25, the standard guidelines say you should get tested for gonorrhea and chlamydia if you have a new partner or partners, or if you’ve had unprotected sex.

...you’re in a dry spell, but you got tested for all STDs soon after the most recent time you had sex.

Good job! But you might want to get tested again. It takes six months after infection for an HIV test to show up as positive, Hook explains. That means if you ran out and got tested right away, it would have been too soon for the disease to present.

...you’re currently having casual sex:

“If you have a new partner, ideally you both would be tested together ahead of time and have full disclosure,” Pizarro says. But it doesn’t always work that way in real life, which is why using barrier methods like condoms and dental dams is a must, he says.

So is getting tested more often than once a year. “If you have multiple partners, particularly if you’re not using [protection], you should consider more frequent testing,” Hook says. He recommends at least every six months.

...you’re just starting a relationship:

Honestly, if you’re serious about each other, you should go get tested tomorrow—or at least before you start having unprotected sex (and ideally before that, since there are some STDs condoms don’t protect against). “Getting tested is not a matter of distrust, it’s a matter of respect for one another,” Hook says. “It allows people to enter the relationship with confidence about their partner’s status, which is optimal if they want to move forward in a sexual relationship and not have to worry about things like condoms unless there are other reasons for doing so.”

It doesn’t need to happen the very day you define the relationship. But it’s good to have that information so that if either of you has an STD, you can get rid of it or start any necessary treatment early on in the relationship.

...you’re in a long-term relationship:

Doctors will offer testing based on the above recommended guidelines for your age, risk factors, and symptoms. What you do with that is up to you. You could decide to get tested three times in the relationship, and if nothing crops up, hold off on further testing unless your relationship status changes, Hook says. Or, when your doctor brings up testing, you can talk it out with them.

“If a patient’s in a relationship and feels like they haven’t been exposed and would rather not be tested—although plenty of patients have been exposed in committed relationships and end up with surprises—I would certainly have to respect that,” Pizarro says.

Keep in mind that if you’re polyamorous or in an open relationship, you may require more frequent testing depending on your specific situation. Your doctor can offer more guidance on that front.

And if you start to experience strange symptoms, you or your partner has cheated, or anything else makes you think you might have been exposed to an STD, you should definitely get tested, Pizarro says.

...you have previously tested positive for an STD, no matter your relationship status:

Your doctor will help you figure out a treatment plan, but you should also make a follow-up appointment six months after originally testing positive. “Any woman who has one STD diagnosed and treated is more likely to have an STD again within the next six months,” Hook says. Getting tested might be scary, but along with practicing safe sex, it’s one of the most empowered ways to take control of your health.