Sexually Transmitted Infections (STIs): Testing, Results and Prevention

How STIs spread

STIs spread through semen, vaginal fluids, blood and direct contact with infected skin or mucous membranes. Oral and anal sex can transmit most of them, and some (herpes, HPV, syphilis, mpox) spread through skin contact even when a condom is used. Several also pass from mother to baby in pregnancy or birth, and HIV, hepatitis B and syphilis spread through shared needles.

You cannot catch an STI from toilet seats, swimming pools, cutlery or hugging.

Common STIs at a glance

For a symptom-by-symptom overview, see our page on STDs.

When to get tested after possible exposure

Tests only detect an infection after a window period, the time the body or the test needs to show it. Testing too early can give a false negative. If you have symptoms, test right away regardless.

A negative test before the end of the window should be repeated. Test all sites you have had sex with: throat and rectal swabs pick up infections that a urine test misses.

Who should be tested routinely

Based on CDC and USPSTF recommendations:

• Everyone aged 13 to 64: HIV test at least once; all adults should have a hepatitis C and hepatitis B test at least once.
• Sexually active women under 25: chlamydia and gonorrhea every year, and older women with new or multiple partners.
• Gay, bisexual and other men who have sex with men: at least yearly syphilis, chlamydia, gonorrhea and HIV tests at all exposed sites, every 3 to 6 months if higher risk.
• Pregnant people: syphilis, HIV and hepatitis B early in every pregnancy, hepatitis C, and chlamydia and gonorrhea if under 25 or at risk. Syphilis testing is repeated later in pregnancy in many areas.
• People on HIV PrEP: every 3 months.
• People with HIV: at least yearly STI testing.

STI symptoms to watch for

• unusual vaginal discharge or bleeding between periods or after sex
• discharge from the penis, burning or itching
• pain on urination
• sores, blisters, ulcers or warts on the genitals, anus or mouth
• pelvic pain or pain during sex
• testicular pain or swelling
• rectal pain, discharge or bleeding
• a rash on the body, palms or soles, fever and swollen glands

What to do if your STI test is positive

1. Take all treatment as prescribed. Most bacterial STIs are cured with a single injection or a short course of tablets.
2. Avoid sex for 7 days after single-dose treatment or until a course is complete and symptoms have gone.
3. Tell your partners from the last 60 days (90 days for syphilis or longer depending on stage) so they can be tested and treated. Health departments and clinics can notify partners anonymously. In many US states, your clinician can give you medicine to pass to your partner (expedited partner therapy).
4. Get retested for chlamydia, gonorrhea and trichomoniasis about 3 months later, because reinfection is common.
5. Test for other STIs, including HIV and syphilis, since they often occur together.

Untreated STIs can cause pelvic inflammatory disease, infertility, ectopic pregnancy, chronic pain, complications in newborns, nerve and heart damage from syphilis, cervical and other cancers from HPV, and a higher risk of acquiring or passing on HIV.

How to prevent STIs

• Condoms and dental dams: used correctly every time, they greatly reduce the risk of most STIs.
• Vaccines: HPV vaccine (routinely at 11 to 12, recommended up to 26, and possible up to 45 after discussion) and hepatitis B vaccine for all adults up to 59, and older adults at risk. Hepatitis A vaccine and mpox vaccine for those at risk.
• HIV PrEP: daily tablets or long-acting injections for people at increased risk, which prevent HIV very effectively.
• HIV PEP: a 28-day course of HIV medicines started within 72 hours after a possible exposure.
• Doxy-PEP: a single dose of the antibiotic doxycycline taken within 72 hours after sex, recommended by CDC for gay and bisexual men and transgender women who have had a bacterial STI in the past year. It lowers syphilis and chlamydia risk substantially, and gonorrhea to a lesser degree.
• U=U (undetectable equals untransmittable): people with HIV who keep an undetectable viral load on treatment do not transmit HIV sexually.
• Regular testing and open conversations with partners about testing.
• Fewer partners and mutual monogamy with a tested partner reduce risk.

Frequently asked questions

How soon after unprotected sex should I get tested?

For chlamydia and gonorrhea, test about 2 weeks after. For syphilis and HIV, test at about 6 weeks and again at 3 months to be sure. If you have symptoms, get tested immediately. If HIV exposure was in the last 72 hours, ask urgently about PEP.

Can you have an STI without symptoms?

Yes. Most chlamydia, many gonorrhea and trichomoniasis infections, and early HIV, hepatitis B and HPV cause no symptoms. You can still pass them on and develop complications, which is why regular testing is recommended for sexually active people.

Are STIs curable?

Chlamydia, gonorrhea, syphilis and trichomoniasis are curable with antibiotics or antiparasitic medicine. Herpes, HIV and chronic hepatitis B are not curable but are controlled with medicine. HPV is usually cleared by the immune system within 2 years.

What is the difference between an STI and an STD?

They mean much the same thing. STI (infection) is the preferred medical term because many infections cause no symptoms or disease. STD (disease) is still widely used, especially in the US.

Can you get an STI from oral sex?

Yes. Gonorrhea, chlamydia, syphilis, herpes and HPV can all be spread through oral sex. Throat infections are often symptomless, so ask for a throat swab if you have oral sex. Condoms and dental dams reduce the risk.

What is doxy-PEP?

Doxy-PEP is a single dose of the antibiotic doxycycline taken within 72 hours after condomless sex to prevent bacterial STIs. CDC recommends it for gay and bisexual men and transgender women who have had syphilis, chlamydia or gonorrhea in the past 12 months.