Preventing STIs comes down to a combination of barriers, medications, vaccines, and regular testing. No single method eliminates all risk, but layering several strategies together gets close. Here’s what actually works and how effective each approach is.
Condoms Remain the Foundation
External (male) condoms are still the most accessible and well-studied form of STI prevention. When used correctly and consistently, they reduce the risk of gonorrhea by about 90% and chlamydia by roughly 60%. For HIV, consistent condom use cuts transmission risk by approximately 85%. The key phrase is “correctly and consistently,” meaning every time, from start to finish, with no breakage or slippage.
Internal (female) condoms offer a similar type of protection and give the receptive partner more control. They’re less studied than external condoms, but research shows meaningful reductions in chlamydia, gonorrhea, and HIV risk. Internal condoms can also be inserted ahead of time, which some people find more practical.
For oral sex, dental dams create a barrier between the mouth and genitals or anus. In practice, very few people use them: only 10% to 15% of women receiving oral sex have ever tried one. There isn’t enough data to pin down exactly how much they reduce risk, partly because so few people use them consistently. Still, oral transmission of herpes and other infections is real, and dental dams are worth considering if you have multiple partners or a partner with an unknown STI history.
Vaccines That Prevent STIs
Two STIs are preventable with vaccines: HPV and hepatitis B.
The HPV vaccine is recommended at ages 11 to 12, but catch-up vaccination is available through age 26 for anyone who wasn’t vaccinated earlier. Adults 27 through 45 who haven’t been vaccinated can also get it after discussing their risk with a provider. HPV causes genital warts and is the primary driver of cervical, throat, and anal cancers, so this vaccine does double duty as both STI prevention and cancer prevention. If you started at age 15 or older, you’ll need three doses. Starting before 15 requires only two.
The hepatitis B vaccine is a routine childhood immunization, but many adults missed it. If you weren’t vaccinated as a child, the adult series is typically two or three doses depending on the specific vaccine used. Hepatitis B spreads through sexual contact and can cause chronic liver disease, so completing this series is straightforward and highly protective.
PrEP for HIV Prevention
Pre-exposure prophylaxis (PrEP) is a prescription medication that reduces the risk of getting HIV from sex by about 99% when taken as prescribed. For people who inject drugs, it reduces risk by at least 74%. PrEP is available as a daily pill or as a long-acting injection given every two months.
PrEP is designed for people who are HIV-negative but have an ongoing risk of exposure. That includes anyone with an HIV-positive partner, people who don’t consistently use condoms with partners of unknown status, and people who inject drugs. Your provider will test you for HIV before starting and periodically while you’re on it.
Emergency Options After Exposure
If you think you were exposed to HIV, post-exposure prophylaxis (PEP) can prevent infection, but timing is critical. PEP must be started within 72 hours of exposure, and the sooner the better. Every hour counts. The treatment lasts 28 days. PEP is available through emergency rooms, urgent care clinics, and sexual health clinics. It’s meant for emergencies like condom failure, sexual assault, or a known exposure, not as a routine prevention strategy.
For bacterial STIs, a newer option called doxy-PEP is now recommended by the CDC for certain groups. It involves taking a single dose of the antibiotic doxycycline within 72 hours after sex. In clinical trials, this reduced syphilis and chlamydia infections by more than 70% and gonorrhea infections by about 50%. The CDC currently recommends doxy-PEP specifically for gay and bisexual men and transgender women who have had at least one bacterial STI in the past year. If you fall into that category, it’s worth asking your provider for a prescription to keep on hand.
Testing Catches What Prevention Misses
Regular screening is a core part of STI prevention because many infections, especially chlamydia, gonorrhea, and HIV, often produce no symptoms at all. You can carry and transmit an infection for months without knowing it. Getting tested and treated breaks that chain.
The CDC recommends that everyone between ages 13 and 64 get tested for HIV at least once. Beyond that baseline, the frequency depends on your risk profile:
- Women under 25 who are sexually active should be tested for gonorrhea and chlamydia every year.
- Women 25 and older with risk factors (new partners, multiple partners, or a partner with an STI) should also test annually for gonorrhea and chlamydia.
- Gay and bisexual men should test for syphilis, chlamydia, and gonorrhea at least once a year, and for HIV at least annually. Those with multiple or anonymous partners should test every 3 to 6 months.
- Pregnant women should be tested for syphilis, HIV, hepatitis B, and hepatitis C early in pregnancy, with repeat testing if risk factors are present.
Many STI tests are simple urine samples or blood draws, and results typically come back within a few days. Free or low-cost testing is available at most public health departments and sexual health clinics.
Treating Partners Prevents Reinfection
One of the most overlooked parts of STI prevention is making sure your sexual partners get treated too. If you’re diagnosed with chlamydia or gonorrhea, your current partners need treatment even if they feel fine. Otherwise, you’ll likely get reinfected the next time you have sex with them.
Expedited Partner Therapy makes this easier. Your provider can give you a prescription or medication to bring directly to your partner, so they can be treated without a separate clinic visit. This is particularly useful when a partner is unlikely to seek care on their own. It’s legal in most states and is specifically endorsed by the CDC for chlamydia and gonorrhea.
Layering Methods for Maximum Protection
No single prevention method covers every STI. Condoms are excellent for gonorrhea and HIV but less effective against herpes and HPV, which spread through skin-to-skin contact in areas the condom doesn’t cover. PrEP only protects against HIV. Vaccines only cover HPV and hepatitis B. The most effective approach is combining several layers: consistent condom use, vaccination, PrEP if you’re at risk for HIV, regular testing, and prompt treatment when infections are found.
Reducing your number of concurrent sexual partners also lowers your overall exposure risk, though it’s not a substitute for the methods above. Mutual monogamy with a tested partner is highly protective, but only if both partners have actually been tested and confirmed negative before relying on that status.