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Sexually Transmitted Infections (STIs)

What are sexually transmitted infections (STIs)?

STIs are infections passed from person to person through sexual contact. They may also be called STDs for sexually transmitted diseases. Millions of new cases are diagnosed every year in the U.S. According to the CDC, 15- to 24-year-olds make up half of all new STIs.

How can you protect yourself from STIs?

The best way to prevent getting an STI is to not have sex, including oral, vaginal, or anal sex. But you can take steps to lower your risk for an STI if you decide to become sexually active or are currently sexually active. These include:

  • Use a male latex condom the correct way every time you have sex. Or use a female polyurethane condom plus medicine that kills sperm (topical spermicide).

  • Prevent and control other STIs. Having one STI may increase your risk for others.

  • Get the HPV vaccine before having sex for the first time or as soon as possible after becoming sexually active.

  • Delay having sexual relationships as long as you can. The younger you are when you start having sex, the more likely you are to get an STI.

  • Limit the number of sexual partners you have. As an example, some couples decide to be "mutually monogamous," meaning only being sexually active with each other while dating or living together. This greatly lowers the risk of STIs to either of you.

  • Talk to your partners about your and their past STIs and HIV testing status, and whether either of you have any current STIs or genital symptoms. If you're in an ongoing relationship with someone, consider both going for STI and HIV testing now. Share your results with each other when they return. Some people decide to do rapid at-home HIV saliva tests together, although these are not as accurate as having blood HIV tests.

  • Have regular checkups for HIV and STIs.

  • Learn the symptoms of STIs and seek medical help as soon as possible if any symptoms develop.

  • Don't have sexual intercourse during your monthly period.

  • Don't have anal intercourse. Or if you do, use a latex condom and medicine that kills sperm.

  • Don't douche.

  • Talk with your healthcare provider if you have had an STI or have multiple sexual partners. Ask your provider about preventing HIV infection by taking a preventive medicine. This is called PREP (pre-exposure prophylaxis).

  • Start taking PEP medicines as soon as possible after sex if you had unprotected sex with a partner who is HIV-positive or you don't know their HIV status. PEP is a combination of antiviral medicines. The medicines should be taken no later than 72 hours after sex. They can help to prevent you from getting HIV. If your partner is HIV-positive, but taking their antiretroviral medicine regularly and their virus is undetectable, you are at little risk for HIV. You would not need to take PEP.

  • If you have been exposed or diagnosed with an STI, ask your healthcare provider if your partner should be tested and treated as well and what precautions you should be taking. Your provider may talk with you about expedited partner therapy (EPT). With EPT, you may be given a prescription or medicines to give to your partner without your partner needing to be seen by the provider. EPT is available in many states for some STIs (mainly chlamydia and gonorrhea). State laws vary, so talk to your provider.

What to do when diagnosed with an STI?

  • Begin treatment right away. Take the full course of medicines and follow your healthcare provider's advice.

  • Tell your recent sexual partners so that they can get tested and treated, too.

  • Tell your local health department about all recent sexual partners, so that they can be informed even if you haven't been able to tell them. The health department will tell them in a confidential manner, without revealing your identity.

  • Don't have sexual activity while getting treatment for an STI. Ask your healthcare provider when it is safe to have sex again.

What are some common types of STIs?

Common STIs are listed below.


HIV is a virus that destroys the body's ability to fight infection. People who have HIV may not look or feel sick for a long time after infection. If you are not diagnosed early and treated, you are at high risk of developing many life-threatening diseases and certain forms of cancer. The virus is passed on most often during sexual activity. It can also be passed on by sharing needles used to inject drugs. HIV can be passed to your baby during pregnancy, and labor and delivery, and through breastfeeding. If you know before becoming pregnant or early in your pregnancy that you are HIV-positive, you can get treatment that greatly lowers your chance of passing on the virus to your child. Someone who is HIV-positive but takes their antiretroviral medicine regularly and their virus is undetectable in the blood continuously for 6 months or more can't spread HIV to their partner.

Human papillomavirus (HPV)

HPV is one of the most common STIs. Some types of HPV can cause genital warts. These can happen on the inside or outside areas of the genitals. They may spread to the surrounding skin or to a sexual partner. Many other types of HPV cause no symptoms, so you may not know that you are infected. In most cases, the virus goes away and doesn't cause more health problems. But if the virus lasts, normal cells can change and become abnormal. Women with an HPV infection with high-risk types, such as HPV 16 and 18, have an increased risk of getting cervical cancer. Pap tests can find HPV infection, as well as abnormal cervical cells. An HPV vaccine protects against the types of HPV that cause most cervical cancers. It also protects against most genital warts in both men and women, and against anal cancer in men. Even with treatment for genital warts, the virus remains in the body and warts can reappear. Certain types of HPV can also cause warts on other body parts, such as the hands. These are called common warts. These don't generally cause health problems. If a pregnant woman has a large number of genital warts, the growths can complicate a vaginal delivery. If the warts block the birth canal, the woman may need a cesarean section. 


Chlamydia is the most commonly reported STI in the U.S. It can affect both men and women. It often causes no symptoms. If symptomatic, the infection may cause an abnormal genital discharge and burning with urination. In women, untreated chlamydia may lead to pelvic inflammatory disease (PID). Chlamydia can be treated with antibiotics. The most common and serious complications occur in women. In addition to PID, these include tubal (ectopic) pregnancy and infertility. Chlamydia can also be carried in and affect the rectum and throat. If you are pregnant and have chlamydia, the infection can be passed to your baby at birth. This can cause eye infections or pneumonia in your baby. With chlamydia, you are also more likely to have your baby too early. 


Gonorrhea may be present but cause no symptoms. Or it can cause a discharge from the vagina, penis, or rectum, painful or difficult urination or bowel movements, or a sore throat that doesn't go away. The most common and serious complications happen in women. They include PID, tubal pregnancy, and infertility. Men can also get infection of the prostate or epididymis. Gonorrhea can be treated with antibiotics. Gonorrhea at the time of childbirth can spread to the baby and cause severe eye infection. 

Genital herpes

Genital herpes infections are caused by the herpes simplex virus (HSV). Symptoms may include painful blisters or open sores in the genital, buttock, or rectal area. Tingling or burning sensation in the legs, buttocks, or genital area may happen just before the blisters show up. The herpes sores usually disappear within a few days. The virus stays in the body for life, and the sores may return from time to time. There is no cure for HSV. But medicine can shorten an outbreak and ease symptoms. It can also be used to prevent outbreaks and lower the risk of spreading HSV to your sexual partners. HSV can be passed on from the mouth to the genitals, or from the genitals to the mouth, during oral sex. The virus can be passed on to sexual partners even if the person has no visible blisters. This is from so-called asymptomatic shedding of the infection. HSV can also be spread to a baby at the time of childbirth. This causes a very severe infection in the baby. 


The first symptom of syphilis is a painless open sore that usually shows up on the penis, in the vagina or mouth, or on the skin around the rectum or genitals. Untreated syphilis may go on to more advanced stages. These include a rash. Over time it can cause problems with the heart and central nervous system. Syphilis can be treated with antibiotics. If a pregnant woman has untreated syphilis, the disease can cause dangerous, even fatal, problems for the baby. The way congenital syphilis affects the baby depends on how long the woman has had the disease and if or when she was treated for the infection. This form of syphilis can cause miscarriage, stillbirth, or death of the baby shortly after birth. Untreated babies that do survive will likely develop serious multiple organ problems of the brain, heart, eyes, and ears.

Other infections

Other infections that may be sexually transmitted include:

  • Bacterial vaginosis

  • Chancroid

  • Molluscum contagiosum

  • Pubic lice

  • Scabies

  • Trichomoniasis

  • Vaginal yeast infections

What are the facts about STIs and teens?

STIs affect men and women of all backgrounds and economic levels. But nearly half of all STIs in the U.S. happen in people younger than age 25.

STIs are on the rise. This may be because more sexually active people have multiple sex partners during their life.

Many STIs cause no symptoms at first. Also, many STI symptoms may look like those of other diseases not transmitted through sexual contact. This is especially true in women.  STIs without symptoms can still be spread to other people.

Women suffer more severe symptoms from STIs:

  • Some STIs can spread into the womb (uterus) and fallopian tubes and cause PID. This can lead to both infertility and tubal pregnancy.

  • STIs in women, especially HPV infection, also may lead to cervical and anal cancer. Men can also get penile and anal cancer from HPV infection.

  • STIs can be passed from a mother to her baby before or during birth. Some infections of the newborn may be successfully treated. Others may cause a baby to be permanently disabled or even die.

Many STIs can be successfully treated when diagnosed early.

Online Medical Reviewer: Barry Zingman MD
Online Medical Reviewer: L Renee Watson MSN RN
Online Medical Reviewer: Melinda Murray Ratini DO
Date Last Reviewed: 5/1/2023
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