You don't need another doctor telling you about the dangers of unprotected sex. If you're reading this, you've probably been primed: infections contracted through sex, if left untreated, can cause health problems ranging from infertility to chronic pain to cancer. But in many (if not most) circles, talking about sexually transmitted infections is still taboo, and so many women have no idea if, when, and how they should be screened.
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First, let's straighten out some terminology. We're talking about infections - some asymptomatic, many curable, and virtually all treatable - so let's move away from the term "sexually transmitted diseases" and start calling them sexually transmitted infections, or STIs. Keep in mind, though, that the terms tend to be interchangeable and what you consider an STD may actually be an STI, so it's the more correct term we should actually be using.
Another clarification: I'm talking about screening, which by definition is a test performed in someone without evidence of disease. If you have any symptoms concerning a possible STI (things like changes in urination, bleeding, discharge, pelvic pain, or painful sex), then these rules don't apply to you - talk to your doctor right away. But if you're asymptomatic, the following is a rough guide for if and when you should get yourself checked for each major type of STI.
Chlamydia and Gonorrhea
Because these two are so common - over 1.5 million cases of chlamydia and half a million cases of gonorrhea were reported in the US last year - the CDC recommends that all women 25 and under get tested annually. If you're older than 25, how often you get tested will depend on your unique risk factors. Women at higher risk should also be tested every year. If you've recently had a new sexual partner, have multiple sexual partners, have a partner with a recently diagnosed STI, or have a partner with other concurrent partners, you fall into this high-risk category - especially if you don't use barrier protection consistently.
Everyone should be tested at least once for HIV during adolescence or adulthood. Although there are no formal guidelines on repeat screening for women, those who are higher risk based on the factors above should be tested more frequently. Some doctors will screen "highest-risk" women, including those who have multiple sexual partners who do not use barrier protection, every six months. Because it can take up to 12 weeks for the usual screening test for HIV to show as positive, if you're getting tested soon after having sex with a new partner, make sure to discuss alternative testing options or get retested after a few months.
Even though it's on the rise, unlike HIV, screening for syphilis is only recommended if you fall into a higher-risk category based on your sexual history. Because syphilis is often found in the setting of other sexually transmitted infections, if you do get diagnosed with an STI, your doctor should test you for syphilis as well.
Screening for HPV, or human papillomavirus, is done with your pap smear starting at age 30. HPV is prevalent in sexually active women in their 20s, but the vast majority of cases are asymptomatic and cleared spontaneously, so it's not worth checking until you're a bit older. Many of us grew up in a time when pap smears were performed annually, but according to new guidelines, you actually only need one every three years. If you test positive for certain strains of HPV - those known to be associated with cervical cancer - your doctor may recommend more frequent paps.
Doctors rarely screen for the herpes viruses HSV-1 and HSV-2 because they're so overwhelmingly common that it's probably not worth finding out if you have it unless you have symptoms. About half of women test positive for antibodies to HSV-1 or HSV-2 (indicating they've been exposed at some point), but unless you get hallmark breakouts of bothersome genital sores, there is no indication for treatment, so you're probably better off being blissfully ignorant.
Hepatitis B and C
All women born between 1945 and 1965 should have a one-time screening for Hepatitis C. Everyone else should be tested for Hepatitis B and C depending on risk factors. If you're at an elevated risk based on the factors mentioned above, you should be checked at least once and probably yearly for as long as you remain in a higher-risk category.