Patient education: Sexually transmitted infections (The Basics)

Written by the doctors and editors at UpToDate

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What are sexually transmitted infections? —

Sexually transmitted infections ("STIs") are infections you can get through sex. They are also called sexually transmitted diseases ("STDs").

Most STIs are caused by bacteria or viruses. Some are caused by parasites.

The most common STIs include:

●Chlamydia

●Gonorrhea

●Mycoplasma genitalium

●Genital herpes, also called herpes simplex virus ("HSV")

●Genital warts, also called human papillomavirus ("HPV") – Some types of HPV can cause cancer of the cervix, penis, or anus.

●Hepatitis B

●Syphilis

●Trichomoniasis

●Human immunodeficiency virus ("HIV") – This is the virus that causes AIDS.

Many of these can be spread through any type of sex. That includes vaginal, anal, and oral sex, as well as other types of sex play. HIV and hepatitis B can be spread in other ways, too, such as exposure to body fluids.

Other infections can also be spread through sex. These include:

●Hepatitis A and hepatitis C – These are other types of hepatitis viruses. They are usually spread in other ways. But they can also be spread through sex.

●Zika virus – This is usually spread through mosquito bites. But it can also be spread through sex.

●Neisseria meningitidis – This can be spread during close contact, including through sex. It has caused small outbreaks of bacterial meningitis in males who have sex with males.

●Mpox (also known as monkeypox) – This is a viral infection that can be spread during close contact, including through sex.

What is STI screening? —

"Screening" means testing for STIs in a person who does not have symptoms. Screening is very important. That's because STIs often do not cause symptoms, so a person can have an STI and not know it.

Doctors recommend people who are at risk for STIs be screened even if they feel healthy. For example, you could be at risk for chlamydia if you had unprotected sex with a new partner. Screening for chlamydia will show if you have the infection, so you can get treatment. Treatment prevents the infection from getting worse and keeps you from infecting other people.

There are different types of tests that screen for different infections. Many STIs can be found through a blood or urine test. If you decide to get screened for STIs, your doctor or nurse can work with you to figure out which specific tests you need.

Who should be tested for STIs? —

If you think you might have an STI, or if you had sex with someone who has an STI, you should get tested.

For screening, different tests are appropriate for different people, depending on their sex and sex habits. Some general guidelines:

●All people (including teens) should get screened at least once for HIV.

●All females younger than 25 years who have had sex should be screened every year for gonorrhea and chlamydia.

●Females older than 25 who have sex with more than 1 partner and do not use condoms should be screened every year for gonorrhea and chlamydia.

●Males who have sex with males should be screened at least once a year for HIV, syphilis, chlamydia, and gonorrhea. This should include testing of any body parts that could be infected, including the rectum. Males who have sex with males should also be screened at least once for hepatitis A, B, and C.

●Pregnant people should be screened for syphilis, HIV, and hepatitis B. They should also be screened for chlamydia and gonorrhea if they are younger than 25 years or have more than 1 sex partner. Some pregnant people might also need to be screened for other infections, depending on their sex habits.

●All people who are infected with HIV should be screened at least once for hepatitis A, B, and C. They should also be screened at least once a year for syphilis, chlamydia, and gonorrhea. Females who are infected with HIV should be screened at least once a year for trichomonas. Males who are infected with HIV, and who have sex with males with HIV, should be screened at least once a year for hepatitis C.

●Transgender and gender-diverse people should be screened based on their anatomy and sex habits.

Some people might need other screening tests depending on their sex habits and other factors. If you are unsure whether you should be screened and for what, ask your doctor or nurse.

Where can I get an STI test? —

There are a few options:

●If you see a doctor or nurse regularly, they can test you.

●You can go to a clinic. To find a clinic near you, check with your local Department of Health or visit www.plannedparenthood.org. Some clinics let you get tested without giving your name (anonymously).

Be careful with any pharmacies or online stores that sell kits to use at home to screen for STIs. For some of these tests, you send in a sample, and then you get the results either by phone or online. For others, you do a test at home and get results within an hour. But it is not always clear which test kits you can trust. If you do use 1 of these kits and get a positive result, follow up with a doctor or nurse. If you get a negative result but think you might have an infection, see a doctor or nurse.

What symptoms should I watch for? —

Many STIs do not cause any symptoms, and some symptoms can come and go.

Some symptoms to watch for include:

●Genital itching, burning, sores, or discharge

●Pain or bleeding from sex

●New or unusual vaginal bleeding

●Swelling and pain in the testicles

The best way to know for sure if you have an STI is to be tested.

How are STIs treated? —

The right treatment depends on the type of STI. Treatment might include antibiotics or "antiviral" medicines, which fight viruses. Treatment can cure your infection or keep it from getting worse. It can also lower the chance of spreading the infection to others.

If you do have an infection, you might need to tell the people you could have infected. Your doctor or nurse can help you figure out which partners to tell based on when you last had sex with them.

Can STIs be prevented? —

There is no definite way to prevent all STIs. But there are things you can do to lower your chances of getting one:

●The most important thing you can do is to use a condom correctly every time you have sex:

•Doctors recommend external (male) condoms to protect against STIs (figure 1). Internal (female) condoms might also reduce the chances of getting an STI (figure 2). But internal condoms have not been tested as much as external ones.

•Condoms made out of "natural materials," such as sheep intestine, do not protect against STIs.

●Talk to any new partners about STIs before you have sex. Share when you were last tested and if you have any other partners.

●Do not have sex when you or your partner has symptoms that could be from an STI. This includes if either of you have herpes and are having an "outbreak." This is when there are blisters and open sores in the genital area.

●Ask your doctor if you should get any vaccines. If you are 26 years old or younger, you can get a vaccine to protect against HPV, the virus that causes genital warts and cervical cancer. Some older people can also get the HPV vaccine. If you do not have hepatitis A or B and have not already gotten the vaccine for hepatitis A or B, you can get those vaccines, too. Your doctor might also suggest a meningitis or mpox vaccine if you are at risk.

●If your partner has herpes, they can take a medicine called valacyclovir (brand name: Valtrex). This lowers the chances of passing the infection to you.

●If your partner has HIV, taking HIV medicines can lower the amount of virus in their blood. This can help prevent spreading HIV to you, but they must take the medicine exactly as instructed.

●If you are at very high risk for certain STIs, talk to your doctor about whether you should take medicines to lower the risk. For example:

•Taking an antiviral pill every day can lower the risk of getting HIV.

•For some people, taking an antibiotic pill after sex can lower the risk of getting chlamydia, syphilis, and gonorrhea. But this does not work for everyone.

If you use sex toys, it is best not to share them with anyone else and to wash them between each use. This might help prevent spreading some STIs.

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This topic retrieved from UpToDate on: May 11, 2025.

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Patient education: Sexually transmitted infections (The Basics)