Preventing sexually transmitted infections comes down to a layered approach: barriers, vaccines, medication, testing, and honest communication with partners. No single method is perfect on its own, but combining several of them dramatically lowers your risk. Here’s what actually works and how well each strategy performs.
Condoms: Effective but Not Equal Against All STIs
External (male) condoms are the most widely available and well-studied barrier method. For HIV, consistent and correct use reduces transmission by about 85%, with overall protection exceeding 90%. For bacterial infections like chlamydia and syphilis, the picture is more nuanced. Consistent condom use reduces syphilis transmission by 50 to 71%, while one prospective study found zero chlamydia infections among condom users compared to a 6.3% infection rate among non-users.
The reason condoms work better against some infections than others has to do with how those infections spread. HIV transmits through bodily fluids, so a physical barrier over the main fluid exchange point is highly effective. Syphilis and herpes, on the other hand, can spread through skin-to-skin contact with sores or infected areas that a condom doesn’t cover. That’s why syphilis protection with typical (imperfect) use drops to around 29%. Condoms still help significantly, but they aren’t a complete shield for infections that live on exposed skin.
Internal (female) condoms offer a similar barrier and cover a slightly larger area, which may provide modestly better protection against skin-contact infections. They’re a good option when an external condom isn’t being used.
Why Lubricant Choice Matters
Oil-based lubricants, including baby oil, petroleum jelly, body lotion, and vegetable oil, weaken latex condoms. Lab testing has shown that mineral oil-based products cause significant degradation of latex, increasing the chance of breakage during sex. This applies to any latex or polyisoprene condom. If you’re using condoms, stick with water-based or silicone-based lubricants. Silicone-based lubes are fine with latex but can damage silicone toys, so water-based is the most universally compatible choice.
Barriers for Oral Sex
Dental dams are thin sheets of latex or nitrile placed over the vulva or anus during oral sex. The research on their effectiveness is limited, largely because so few people use them that studies can’t reach statistical significance. That said, since condoms clearly reduce STI risk for penetrative sex, public health experts reason that any physical barrier during oral sex likely offers meaningful protection too. Gonorrhea, syphilis, herpes, and chlamydia can all transmit through oral sex, so using a barrier (or a condom for oral sex performed on a penis) closes a gap many people overlook.
Vaccines That Prevent STIs
The HPV vaccine is the most impactful STI vaccine available. It protects against the nine strains of human papillomavirus responsible for the vast majority of cervical cancers, most anal and throat cancers, and genital warts. The vaccine is approved for people ages 9 through 45, though it works best when given before any HPV exposure, which is why it’s routinely recommended at ages 11 to 12. If you weren’t vaccinated as a teenager, getting it as an adult still offers substantial protection against strains you haven’t yet encountered.
Hepatitis B is another STI preventable by vaccination. Most people born in the U.S. after 1991 received it as infants, but if you’re unsure of your status, a simple blood test can check your immunity. Hepatitis A vaccination is also recommended for men who have sex with men and for anyone at elevated risk.
PrEP for HIV Prevention
Pre-exposure prophylaxis (PrEP) is a prescription medication that prevents HIV infection before exposure. Two forms are available: a daily pill and a long-acting injection given every two months. Both are highly effective, but the injectable version has an edge. In a head-to-head trial, HIV infection occurred in 0.57% of people receiving the injection compared to 1.7% of those taking the daily pill, a roughly threefold difference. The trial was stopped early because the injectable form was so clearly superior.
The daily pill works extremely well when taken consistently, but real-world adherence is the challenge. The injection removes that variable entirely, which is why infection rates were lower. PrEP is recommended for anyone at ongoing risk of HIV, including people with an HIV-positive partner, people who don’t consistently use condoms, and anyone who has had a bacterial STI in the past six months.
Post-Exposure Antibiotics for Bacterial STIs
A newer prevention tool called doxy-PEP uses a single dose of the antibiotic doxycycline taken within 72 hours after sex to prevent bacterial STIs like syphilis, chlamydia, and gonorrhea. The CDC released formal guidelines in 2024 recommending that providers offer doxy-PEP to men who have sex with men and transgender women who have had a bacterial STI in the past 12 months. You take 200 mg as soon as possible after sex, with a maximum of 200 mg in any 24-hour period.
This isn’t a blanket recommendation for everyone. It’s targeted at people with a recent history of bacterial STIs who are at high risk of reinfection. If that describes your situation, it’s worth discussing with a provider, as the evidence for reducing syphilis and chlamydia reinfection in this population is strong. Its effectiveness against gonorrhea is less certain due to rising antibiotic resistance.
How Often to Get Tested
Regular testing is a prevention strategy in itself because many STIs cause no symptoms. You can carry and transmit chlamydia, gonorrhea, or HIV for months without knowing. Catching an infection early means treating it before you pass it on.
CDC screening recommendations vary by risk level:
- All adults ages 13 to 64: At least one HIV test in your lifetime, with repeat testing based on risk.
- Sexually active women under 25: Annual screening for chlamydia and gonorrhea. Women 25 and older should screen if at increased risk.
- Men who have sex with men: HIV, syphilis, chlamydia, and gonorrhea testing at least once a year. Every 3 to 6 months if at higher risk, such as having multiple partners or inconsistent condom use. Gonorrhea and chlamydia testing should cover all sites of contact: throat, rectum, and urethra.
- Anyone with HIV: Screening for syphilis, gonorrhea, and chlamydia at your first evaluation and at least annually after that.
If you’re in a mutually monogamous relationship and both partners tested negative at the start, ongoing screening is less critical. But if either partner has other sexual contacts, the testing intervals above apply.
Telling Partners and Preventing Reinfection
One of the most overlooked parts of STI prevention is what happens after a positive test. If you’re treated for chlamydia or gonorrhea but your recent partner isn’t, reinfection is almost inevitable the next time you have sex with them. Studies show that people whose partners received treatment through expedited partner therapy were 29% less likely to be reinfected compared to those who simply told their partner to visit a clinic. Expedited partner therapy means your provider gives you a prescription or medication to pass directly to your partner, skipping the step where they need to make their own appointment. It’s legal in most U.S. states and worth asking about.
Layering Methods for Strongest Protection
No single method covers every infection. Condoms are excellent for HIV and good for bacterial STIs, but less protective against herpes and HPV. The HPV vaccine handles the strains condoms miss. PrEP covers HIV specifically. Testing catches what slips through. The people with the lowest STI rates aren’t relying on any one of these tools. They’re combining several: using condoms consistently, staying current on vaccines, testing at appropriate intervals, and communicating openly with partners about status and risk.
Reducing your number of concurrent sexual partners also lowers exposure, though it’s the consistency of protection within each encounter that matters most. One partner with an untreated infection and no condom use carries more risk than multiple partners with consistent barrier use and regular testing.