Health Topic

Sexually Transmitted Infections

Sexually transmitted infections (STIs) are passed from person to person during sexual contact. Testing, vaccines, and prevention behaviors can lower your risk.

Reviewed Reviewed by a registered pharmacistGeneral information

Also called: STDs · STIs · Sexually transmitted diseases · Venereal disease

Important: This page is general information, not medical advice. It does not recommend or prescribe any treatment. Always consult your doctor or pharmacist before starting, stopping or changing any medicine.

About Sexually Transmitted Infections

Sexually transmitted infections (STIs) are infections that are passed from one person to another through sexual contact. If not treated, an STI can develop into a sexually transmitted disease (STD).

STIs are usually spread during vaginal, oral, or anal sex. But sometimes they can spread through other sexual contact involving the penis, vagina, mouth, or anus. This is because some STIs, like herpes and HPV, are spread by skin-to-skin contact.

Some STIs can be passed to the fetus during pregnancy or childbirth. Other ways that some STIs may spread include while breastfeeding, through blood transfusions, or by sharing needles.

There are more than 20 types of STIs, including:

  • Chlamydia
  • Genital herpes
  • Genital warts
  • Gonorrhea
  • HIV
  • HPV
  • Pubic lice
  • Syphilis
  • Trichomoniasis

STIs can be caused by bacteria, viruses, and parasites.

Most STIs affect both men and women, but in many cases the health problems they cause can be more severe for women. If an STI is passed to a fetus during pregnancy or childbirth, it can cause serious health problems.

STIs don't always cause symptoms or may only cause mild symptoms. So, it is possible to have an infection and not know it. And even without symptoms, STIs can still be harmful and may be passed on during sex.

If you do have symptoms, they could include:

  • Unusual discharge from the penis or vagina
  • Sores or warts on the genital area
  • Painful or frequent urination (peeing)
  • Itching and redness in the genital area
  • Blisters or sores in or around the mouth
  • Abnormal vaginal odor
  • Anal itching, soreness, or bleeding
  • Abdominal (belly) pain
  • Fever

If you are sexually active, you should talk to your health care provider about your risk for STIs and whether you need to be tested. This is especially important since many STIs do not usually cause symptoms.

Some STIs may be diagnosed during a physical exam or through STI testing. Some tests involve a microscopic examination of a sore or fluid swabbed from the vagina, penis, or anus. Blood tests can diagnose other types of STIs.

Antibiotics can treat STIs that are caused by bacteria or parasites. There is no cure for STIs caused by viruses, but antiviral medicines can often help with the symptoms and lower your risk of spreading the infection.

It's important to get treatment if you have an STI. Some types of STIs can cause serious health problems if they are not treated. Talk to your provider about how long to not have sex after treatment to avoid passing the infection back and forth with your partner.

The surest way to protect yourself against STIs is to not have sex.

If you do decide to have sex, you can lower your risk of getting an STI by:

  • Having you and your partner tested for STIs before having sex.
  • Using a condom every time you have sex. Correct usage of latex condoms greatly reduces, but does not eliminate, the risk of catching or spreading STIs. If you or your partner is allergic to latex, you can use polyurethane condoms.
  • Reducing your number of sex partners. You might even consider "mutual monogamy" with just one partner. This means that you agree to be sexually active only with them, and they agree to be sexually active only with you. But first you should both get tested to make sure that you don't already have an STI.
  • Getting vaccinated against HPV and hepatitis B.

It sits within Women, Infections, Men, Sexual Health Issues, Female Reproductive System and Male Reproductive System.

The lead U.S. institute for this subject is the National Institute of Allergy and Infectious Diseases.

When to speak to someone. Reading about a topic cannot tell you whether it applies to you. Speak to a doctor or pharmacist if symptoms are severe, sudden, getting worse, or simply not going away — and seek emergency care immediately for chest pain, breathing difficulty, sudden weakness or confusion, or a serious allergic reaction.

Research on Sexually Transmitted Infections

7,853 studies areregistered for this condition on ClinicalTrials.gov, the U.S. National Library of Medicine's public registry. A selection is below — the links go straight to the registry entry, not to a summary of ours.

What a registered study does and does not mean. Registration means a study exists and has been declared publicly. It says nothing about whether the treatment being tested works, is safe, or is available to you. Many studies find no benefit — that is what research is for. Never seek out an experimental treatment on the strength of a registry entry alone.

Research currently under way

Research already completed

Study data from ClinicalTrials.gov, a service of the U.S. National Library of Medicine. Retrieved 2026-07-30. Registry entries are supplied by study sponsors and investigators; ClinicalTrials.gov does not verify their scientific validity. PocketsInfo is not affiliated with, and not endorsed by, the NLM or the NIH.

Where to read more

Rather than paraphrase, we point you to the primary sources. Every link below is to a government health agency, a national institute or a recognised medical body — grouped by what you are trying to find out.

Start Here

Symptoms

Diagnosis and Tests

Treatments and Therapies

Prevention and Risk Factors

Related Issues

  • CervicitisMayo Foundation for Medical Education and Research
  • Hepatitis BAmerican Academy of Family Physicians

Statistics and Research

Clinical Trials

Medical subject headings

Clinicians and researchers index this subject under Sexually Transmitted Diseases. These are the terms to use when searching medical literature.

This page is built from the MedlinePlus health topic record for Sexually Transmitted Infections, a service of the U.S. National Library of Medicine (NLM), National Institutes of Health. Information is from MedlinePlus.gov. PocketsInfo is not affiliated with, and is not endorsed by, the NLM or the NIH. Retrieved 30 July 2026.