11 Common Sexually Transmitted Infections (STIs)

Worldwide, there are over 20 sexually transmitted infections (STIs) caused by bacteria, viruses, and parasites. Several like gonorrhea, chlamydia, genital herpes, HPV, and syphilis are widespread, causing hundreds of thousands of new infections in the United States annually. In 2023 alone, an estimated 2.4 million new STI cases occurred.

Some STIs are curable while others are not. Similarly, some can cause overt symptoms (like sores and ulcers) while others remain asymptomatic (without symptoms). If left untreated, an STI can not only lead to serious illness but allow the spread of infection to others. Even with condoms and other forms of safer sex, some STIs are hard to avoid.

An illustration with most common sexually transmitted diseases

Verywell / Brianna Gilmartin

A Note on Gender and Sex Terminology

Verywell Health acknowledges that sex and gender are related concepts, but they are not the same. To accurately reflect our sources, this article uses terms like “male," "female," “man,” and "women" as the sources use them.

Chlamydia

Chlamydia is the most common bacterial STI in the United States, resulting in over 1.6 million infections in 2023. Caused by the bacterium Chlamydia trachomatis, this curable STI mainly affects the cervix in females and the urethra of the penis of males.

A great many women with chlamydia remain asymptomatic. When there are symptoms, they often include pain during sex and discharge from the penis or vagina.

Untreated chlamydia can damage the reproductive tract, causing infertility by blocking structures like the epididymis in males and fallopian tubes in females. Chlamydia can be cured with antibiotics like azithromycin or doxycycline.

Trichomoniasis

Trichomoniasis is the most common non-viral STI in the United States, affecting women four times more often than men. An estimated 1 million new trichomoniasis infections occur each year.

Caused by the parasite Trichomonas vaginalis, this curable STI often causes symptoms like vaginal itching, a frothy discharge, a strong vaginal odor, and pain with sex in females. Trichomoniasis in males is usually asymptomatic.

The biggest concern about untreated trichomoniasis is the risk of pregnancy complications, such as miscarriage and premature birth. Trichomoniasis will often clear on its own within months or years but can be treated with one large dose of an antibiotic like Flagyl (metronidazole).

Gonorrhea

Gonorrhea, also known as "the clap," is another common bacterial STI that accounts for around 600,000 new infections in the U.S. every year. Caused by the bacterium Neisseria gonorrhoea, this curable STI affects the same organs as chlamydia with similar effects. It can also infect the throat if you have oral sex.

As with chlamydia, gonorrhea often causes no symptoms, especially in women. If you get symptoms, you may experience a burning sensation when you pee. Gonorrhea can also cause a white, yellow, or green discharge from the penis or vaginal, or a cough and sore throat if you get oral gonorrhea.

Gonorrhea is commonly treated with a single shot of the antibiotic ceftriaxone. With that said, there is a growing problem of antibiotic-resistant gonorrhea in which the bacterium no longer responds to antibiotics commonly used to kill it. In such cases, other drugs may be needed.

Mycoplasma Genitalium

Mycoplasma genitalium (MG) is a sexually transmitted bacteria that causes symptoms similar to gonorrhea in men and women. It is a common cause of pelvic inflammatory disease (PID) in females and nongonococcal urethritis (NGU) in males.

While NG is less well-known than gonorrhea, it causes more infections year on year. In 2022, between 640,000 and 1.6 million new MG infections were thought to have occurred in the U.S.

MG is usually curable with a single dose of azithromycin, but high rates of antibiotic resistance often require other drugs to fully clear the infection. If left untreated, MG can cause infertility or pregnancy complications like ectopic pregnancy in those with PID.

Human Papillomavirus

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genital warts

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Human papillomavirus (HPV) is thought to be the most common STI overall. Studies suggest that around three-quarters of sexually active people acquire this incurable viral STI at some point in their lives. Most are asymptomatic.

There are many different types of HPV, most of which are low-risk strains that may cause genital warts or no symptoms at all. At least 16 are high-risk strains that have the potential to cause cervical cancer and other types of cancer. The types that cause warts rarely cause cancer.

It is often hard to prevent HPV infection because condoms are only nominally effective. With that said, there is an HPV vaccine typically given at ages 11 or 12 before a child is sexually active that can help prevent the most common high-risk strains.

Genital Herpes

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genital herpes

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Genital herpes is an incurable viral STI mainly caused by herpes simplex virus type 2 (HSV-2). It can also be caused by herpes simplex virus type 1 (HSV-1), the type associated with cold sores that can be passed to the genitals through oral sex.

Over 570,000 new genital herpes infections are reported annually in the U.S. among people ages 14 to 49.

Most people with HSV-1 or HSV-2 have no symptoms but can still pass the virus to others whenever the virus reactivates. In those with symptoms, reactivation can cause an episodic outbreak of painful blisters and sores that can last for one to three weeks. Antiviral drugs can help shorten or prevent such attacks.

Syphilis

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primary syphilis

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Syphilis is a curable bacterial STI caused by the bacterium Treponema pallidum that accounted for roughly 209,000 new cases in 2023.

Syphilis develops in stages. It often starts with a painless sore called a chancre on the penis or labia (although those in the rectum or vagina may be unseen). Left untreated, syphilis can cause a whole-body rash during the secondary stage and severe heart and brain complications if it progresses to the tertiary stage.

Syphilis is transmitted when you come into direct contact with a sore, usually found in and around sex organs. A single large injection of penicillin can usually clear the infection.

HIV

Human immunodeficiency virus (HIV) is a sexually transmitted virus that causes illness by killing defensive immune cells called CD4 T-cells. As more and more of these cells are destroyed, the body becomes less able to defend itself against otherwise harmless infections (known as opportunistic infections).

If left untreated, HIV can lead to the most advanced stage of infection, called acquired immunodeficiency syndrome (AIDS). There are currently 1.2 million people living with HIV in the United States, with over 30,000 new infections reported each year.

HIV cannot be cured, but treatment with antiretroviral drugs can keep the virus fully suppressed so that the immune system remains intact and normal to near-normal life expectancy can be achieved. Antiretrovirals can also protect you from getting infected in a strategy known as pre-exposure prophylaxis (PrEP).

Hepatitis B

Hepatitis B is a viral STI affecting the liver caused by the hepatitis B virus (HBV). HBV is also the one form of viral hepatitis that is sexually transmitted, unlike hepatitis A or hepatitis C.

Most people infected with HBV will spontaneously clear the virus, but those who don't will develop chronic hepatitis B which is not curable. If left untreated, chronic HBV can progress, causing cirrhosis and liver failure in some people.

To date, between 880,000 and 1.89 million people are chronically infected with HBV in the United States. Due to widespread HBV vaccination, the rate of new chronic infections has dropped to around 14,000 per year.

Lymphogranuloma Venereum (LGV)

Lymphogranuloma venereum (LGV) is a curable bacterial STI caused by strains of Chlamydia trachomitis. Although rare, sporadic outbreaks of LGV are seen mainly among men who have sex with men (MSM), with 345 cases reported in the U.S. in 2022.

Unlike chlamydia, LGV causes an initial outbreak of painless ulcers on the genitals, not unlike those seen with syphilis. After 10 to 30 days, the infection will spread through the lymphatic system, causing enlarged painful lymph nodes known as buboes mainly in the groin.

LGV is readily treated with antibiotics. If left untreated, LGV can progress and lead to permanent, irreversible lymphedema (the overload of lymph fluid in tissues).

Chancroid

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Chancroid

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Chancroid is a curable STI caused by the bacterium Haemophilus ducreyi which leads to the formation of painful sores on the genitals. Swollen lymph nodes in the groin (inguinal lymphadenopathy) and a heavy pus discharge are also common.

Chancroid is mainly seen in parts of the Caribbean and Africa, with less than 10 cases reported annually in the U.S. Even so, the formation of an open ulcer can increase the risk of HIV transmission in the same way as herpes or syphilis.

Chancroid is readily treated with non-penicillin antibiotics like cephalosporin, ceftriaxone, azithromycin, and erythromycin.

Summary

The most common sexually transmitted infections (STIs) in the United States are chlamydia, trichomoniasis, human papillomavirus (HPV), genital herpes, mycoplasma genitalum (MG), syphilis, HIV, and hepatitis B. Rare ones include lymphogranuloma venereum (LGV) and chancroid.

Those that are curable are bacterial or parasitic STIs like chlamydia, trichomoniasis, MG, syphilis, LGV, and chancroid. Those that are incurable but treatable include viral STIs like HPV, genital herpes, HIV, and hepatitis B.

22 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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  2. Centers for Disease Control and Prevention. Chlamydia: CDC fact sheet (detailed).

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  4. Centers for Disease Control and Prevention. Trichomoniasis.

  5. Centers for Disease Control and Prevention. Gonorrhea.

  6. Centers for Disease Control and Prevention. Gonorrhea - CDC fact sheet (detailed version).

  7. Centers for Disease Control and Prevention. Mycoplasma genitalium.

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  9. Centers for Disease Control and Prevention. About HPV.

  10. Centers for Disease Control and Prevention. Vaccinating boys and girls.

  11. Centers for Disease Control and Prevention. Genital herpes.

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  13. Centers for Disease Control and Prevention. Syphilis - CDC fact sheet (detailed).

  14. Department of Health and Human Services. What are HIV and AIDS?.

  15. HIV.gov. U.S. statistics.

  16. Trickey A, Sabin CA, Burkholder G, et al. Life expectancy after 2015 of adults with HIV on long-term antiretroviral therapy in Europe and North America: a collaborative analysis of cohort studiesLancet HIV. 2023 May;10(5):e295–e307. doi:10.1016/S2352-3018(23)00028-0

  17. HIV.gov. Pre-exposure prophylaxis.

  18. Department of Health and Human Services. Hepatitis B basic information.

  19. Ceovic R, Gulin SJ. Lymphogranuloma venereum: diagnostic and treatment challengesInfect Drug Resist. 2015;8:39–47. doi:10.2147/IDR.S57540

  20. Gupta AK, Lyon B, Hunter I, et al. The resurgence of lymphogranuloma venereum: changing presentation of lymphogranuloma venereum in the era of HIV preexposure prophylaxis, 2004 to 2022. Sex Transm Dis. 2024 Apr 1;51(4):233-238. doi:10.1097/OLQ.0000000000001944

  21. Centers for Disease Control and Prevention. Chancroid.

  22. Ogale YP, Ridpath AD, Torrone E, Quilter LAS, Grey JA. A sore subject? An examination of national case-based chancroid surveillance. Sex Transm Dis. 2023 August 01;50(8):467–471. doi:10.1097/OLQ.0000000000001814

Additional Reading
Elizabeth Boskey, PhD

By Elizabeth Boskey, PhD
Boskey has a doctorate in biophysics and master's degrees in public health and social work, with expertise in transgender and sexual health.