Sexually transmitted diseases (STDs) are caused by sexually transmitted infections (STIs). They are spread mainly by sexual contact. STIs are caused by bacteria, viruses or parasites. A sexually transmitted infection may pass from person to person in blood, semen, or vaginal and other bodily fluids.

Sometimes sexually transmitted infections are spread in ways other than sexual contact. For example, STIs can spread to infants during pregnancy or childbirth. STIs also can spread through blood transfusions or shared needles.

STIs don't always cause symptoms. A person can get sexually transmitted infections from another person who seems healthy and may not even know they have an infection.


STDs can have a range of symptoms, including no symptoms. That's why sexually transmitted infections may go unnoticed until a person has complications or a partner is diagnosed.

STI symptoms might include:

  • Sores or bumps on the genitals or in the oral or rectal area.
  • Painful or burning urination.
  • Discharge from the penis.
  • Unusual or odorous vaginal discharge.
  • Unusual vaginal bleeding.
  • Pain during sex.
  • Sore, swollen lymph nodes, particularly in the groin but sometimes more widespread.
  • Lower abdominal pain.
  • Fever.
  • Rash over the trunk, hands or feet.

Sexually transmitted infection symptoms may appear a few days after exposure. But it may take years before you have any noticeable problems, depending on what's causing the STI.

When to see a doctor

See a health care professional immediately if:

  • You are sexually active and may have been exposed to a sexually transmitted infection.
  • You have symptoms of a sexually transmitted infection.

Make an appointment with a health care professional:

  • When you're considering becoming sexually active or by age 21, whichever comes first.
  • Before you start having sex with a new partner.

More Information

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Sexually transmitted infections can be caused by:

  • Bacteria. Gonorrhea, syphilis and chlamydia are examples of STDs that are caused by bacteria.
  • Parasites. Trichomoniasis is an STD caused by a parasite.
  • Viruses. STDs caused by viruses include human papillomavirus (HPV), the herpes simplex virus, and the human immunodeficiency virus (HIV), which causes AIDS.

Risk factors

Anyone who is sexually active risks getting or spreading an STD.

Factors that may increase the risk of getting an sexually transmitted infection include:

  • Having unprotected sex. Vaginal or anal sex with an infected partner who isn't wearing a condom (latex or polyurethane) greatly increases the risk of getting an STD. Condoms made from natural membranes aren't recommended because they're not effective at preventing some STIs. Not using condoms properly or not using them each time also can increase risk.

    Oral sex may be less risky. But sexually transmitted infections can still spread if a person doesn't use a condom (latex or polyurethane) or a dental dam. That is a thin, square piece of rubber made with latex or silicone.

  • Having sexual contact with many partners. The more people you have sexual activity with, the greater your risk.
  • Having a history of STIs. Having one sexually transmitted infection makes it much easier for another STI to take hold.
  • Being forced to engage in sexual activity. See a health care professional as soon as possible to get screening, treatment and emotional support.
  • Misuse of alcohol or use of recreational drugs. Substance misuse can inhibit your judgment, making you more willing to take part in risky behaviors.
  • Injecting drugs. Sharing a needle while injecting drugs can spread many serious infections. Examples are human immunodeficiency virus (HIV), hepatitis B and hepatitis C.
  • Being young. People age 15 to 24 report high levels of STIs compared to those who are older.

Spread from mothers to infants

During pregnancy or delivery, some sexually transmitted infections can be passed from mother to infant. Examples are gonorrhea, chlamydia, HIV and syphilis. STIs in infants can cause serious problems or even death. All pregnant women should be screened for STI infections and treated as needed.


Many people in the early stages of an STD have no symptoms. That's why screening is important to prevent complications.

Possible complications of sexually transmitted infections include:

  • Pelvic pain.
  • Pregnancy complications.
  • Eye inflammation.
  • Arthritis.
  • Pelvic inflammatory disease.
  • Infertility.
  • Heart disease.
  • Certain cancers, such as HPV-associated cervical and rectal cancers.


There are many ways to avoid or lower your risk of getting an STD.

  • Avoid sex or sexual activity. The most effective way to avoid STDs is to not have sex.
  • Stay with one uninfected partner. Staying in a long-term relationship in which both people have sex only with each other and neither partner is infected can be one way to avoid an STD.
  • Wait and test. Avoid vaginal and anal sex or sexual activity with new partners until you have both been tested for sexually transmitted infections. Oral sex may be less risky. But STIs can still spread if a person doesn't use a condom (latex or polyurethane) or a dental dam. These barriers prevent skin-to-skin contact between the oral and genital mucous membranes.
  • Get vaccinated. Getting vaccinated before having sex can prevent certain types of sexually transmitted infections. Vaccines are available to prevent STDs caused by human papillomavirus (HPV), hepatitis A and hepatitis B.
  • Use condoms and dental dams consistently and correctly. Use a new latex or polyurethane condom or dental dam for each sex act, whether oral, vaginal or anal. Never use an oil-based lubricant, such as petroleum jelly, with a latex condom or dental dam. Also, these types of barriers give less protection for STDs involving exposed genital sores, such as HPV or herpes.

    Nonbarrier forms of contraception, such as birth control pills or intrauterine devices (IUDs), don't protect against STIs.

  • Don't drink alcohol excessively or use illegal drugs. If you're under the influence of these substances, you're more likely to take sexual risks.
  • Talk to your partner. Before any sexual contact, talk to your partner about practicing safer sex. Be sure you clearly agree on what activities will and won't be OK.
  • Think about male circumcision. For men, evidence has found that circumcision can help lower the risk of getting HIV from a woman with HIV by as much as 60%. Male circumcision may also help prevent spread of genital HPV and genital herpes.
  • Think about using preexposure prophylaxis (PrEP). The U.S. Food and Drug Administration (FDA) has approved two combination medicines to lower the risk of HIV infection in people who are at very high risk. The medicines are emtricitabine plus tenofovir disoproxil fumarate (Truvada) and emtricitabine plus tenofovir alafenamide fumarate (Descovy). These medicines must be taken every day, exactly as prescribed.

Your health care professional will prescribe these medicines for HIV prevention only if you don't already have HIV. You'll need an HIV test before you start taking PrEP and then every three months as long as you're taking it.

Your health care professional also will test your kidney function before prescribing Truvada. They will then test your kidney function every six months. If you have hepatitis B, see an infectious disease specialist or liver specialist before starting therapy.

According to the CDC, if you use Truvada daily, you can lower your risk of getting HIV from sex by about 99%. And you can lower your risk of getting HIV from injection drug use by more than 74%.

Research suggests that Descovy is also effective in lowering the risk of getting HIV from sex. But Descovy hasn't been studied in people who have receptive vaginal sex. Using added prevention, such as condoms, can lower your risk even more and prevent other STIs.

Sept. 08, 2023
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