The Most Common Sexually Transmitted Infections

A sexually transmitted infection (STI, formerly known as a sexually transmitted disease, or STD) is any disease that is spread primarily by sexual contact. One person passes the infection to another during oral, vaginal, or anal sex.

STIs are some of the most difficult diseases to catch. You have to be up close and personal to spread them. So why are STIs so common? The answer may be that people don't know how to recognize, treat, or prevent them. Or when they do, they often don't do so effectively.

An illustration with most common sexually transmitted diseases

Verywell / Brianna Gilmartin

This article explores some of the most common sexually transmitted infections in the United States. It also discusses their causes and symptoms.

Not all diseases that affect the sex organs are considered STIs. In fact, some are not related to sex at all. Others aren't transmitted during sex but occur as a result of it.

Here are some common STIs and diseases associated with sex, along with their symptoms.


Chlamydia is the most common curable bacterial STI. It infects the cervix, which is the opening to the uterus or womb. It can also infect the urethra in a penis.

Many women remain asymptomatic. When there are symptoms, they include pain during sex and discharge from the penis or vagina.

The Centers for Disease Control and Prevention (CDC) recommends that you be screened for chlamydia and other sexually transmitted infections if you are under 25 years old and sexually active. The CDC also recommends screening if you have any of these risk factors:

  • You have a new sex partner.
  • You have a sex partner with an STI.
  • You have more than one sex partner.
  • You have a sex partner who is having sex with other people.

Chlamydia can do a lot of damage to your body in the long run. It can cause infertility by blocking the reproductive tract in men and women. Latex condoms can prevent the spread of this disease.


Gonorrhea, sometimes referred to as "the clap," is another common bacterial STD. It often infects the same organs as chlamydia and has similar long-term effects.

If you have gonorrhea, you may experience a burning sensation when you urinate. The disease can also cause white, yellow, or green discharge from the penis or vagina. It's important to know that many people, especially women, with gonorrhea don't have symptoms.

The CDC estimates that in 2018 there were approximately 1.6 million new gonococcal infections in the U.S.—with more than half occurring in persons aged 15 to 24 years.

Be aware, too, that gonorrhea can also infect your throat if you get it by having oral sex.

Gonorrhea does not always go away when it's treated by antibiotics. There is a growing problem of antibiotic-resistant gonorrhea, which means it no longer dies off with antibiotic drugs that used to kill it.


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primary syphilis

DermNet / CC BY-NC-ND

Syphilis is a common STI with a long history. It's caused by the bacterium Treponema pallidum and can lead to serious health problems if left untreated.

Syphilis is transmitted when you come into direct contact with syphilis sores, which are usually found on the outside or inside of sex organs. They can also appear on your mouth or rectum.

That means it can be transmitted by oral, vaginal, or anal sex. In fact, some scientists think that oral sex is responsible for the rise of syphilis in men who have sex with men.

Syphilis sores can appear on areas not covered by a condom. Condoms lower your risk of getting syphilis, but they don't eliminate it.

At first, syphilis sores (ulcers called chancres) are small and painless. They may heal by themselves, but that doesn't mean the disease is gone. It's just become harder to spot and treat.

Mycoplasma Genitalium (MG)

Mycoplasma genitalium (MG) is starting to emerge as a major cause of infections in the cervix. MG also causes inflammation of the urethra in the penis.

MG can cause the same kinds of symptoms as gonorrhea and chlamydia. In 2007, a well-known study of U.S. teens found that MG infected more people than gonorrhea.

Why did it take so long to recognize MG's importance? Because most cases don't cause symptoms. It was hard to identify until new technology became available. Microbiologic testing is the diagnostic tool of choice for detection of M. genitalium. These are called NAATs (Nucleic Acid Amplification Tests). In the United States, two NAATs have been cleared by the Food and Drug Administration (FDA) for this purpose.

More research on MG is needed. Current research has found a link between MG and serious long-term health problems such as infertility from pelvic inflammatory disease.


Trichomoniasis is the most common nonviral STI worldwide. It affects more women than men. This infection can seem like a yeast infection (fungal infection of the vagina and vulva) or bacterial vaginosis (BV, caused by an overgrowth of bacteria in the vagina) since the symptoms are similar. Symptoms include:

Men with trichomoniasis don't usually have symptoms. If you have been diagnosed with the disease, make sure your partner gets treated. Even if trichomoniasis does not seem to be affecting your partner much, they can still give it back to you, no matter what their sex.

Human Papillomavirus (HPV)

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genital warts

DermNet / CC BY-NC-ND

Human papillomavirus (HPV) may be the most common STI. Studies from before the HPV vaccine was available showed that around three-quarters of sexually active people had HPV at some point. One quarter of women were infected at any given time.

HPV is sometimes called "the cervical cancer virus," but only a few types of HPV can cause cancer. There are other cancers linked to HPV, including penile and anal cancer. Other HPV types cause genital warts, other warts, or no symptoms at all.

There is no cure for HPV, but its symptoms can be treated. Infections can sometimes resolve on their own. It is recommended that 11- to 12-year-olds get the HPV vaccine to protect them from the most common strains of the virus.

The CDC also recommends the HPV vaccine for adults up to age 26 if they were not vaccinated earlier. Some people may receive the vaccine up to age 45.


This photo contains content that some people may find graphic or disturbing.

genital herpes

DermNet / CC BY-NC-ND

Herpes (HSV) is an STI caused by a virus. It comes in two forms: HSV1 and HSV2. HSV1 is often associated with cold sores, and HSV2 is often associated with genital sores. However, it is possible to pass herpes from the mouth to the genitals and vice versa.

Herpes cannot be cured. But its symptoms can be treated with antiviral drugs. You can pass the virus to someone else even if you do not have any sores or other symptoms.

Using a condom lowers the risk of spreading herpes. You can still get herpes even if you use a condom, though.

Herpes can be spread by having sex, but it can also be passed through skin-to-skin contact.


Human immunodeficiency virus (HIV) is the virus that can cause AIDS. It can only be spread by an exchange of bodily fluids. HIV can be spread through:

  • Semen
  • Vaginal fluids
  • Breast milk
  • Blood

HIV cannot be passed by casual contact.

Today, most people with HIV are treated with a combination of drugs known as highly active antiretroviral therapy (HAART), or combined antiretroviral therapy (cART). These therapies cannot cure the disease, but they can reduce the chances of HIV leading to AIDS.

HIV is no longer considered a terminal illness. Many people with the virus are living long and healthy lives.


There are several types of hepatitis. Different viruses are spread through various routes, but they all damage the liver. The type of hepatitis most often spread by sexual contact is hepatitis B (HBV). However, in rare cases, it's also possible to get hepatitis C by having sex with an infected person.

Over time, hepatitis B and C can lead to scarring of the liver, cirrhosis, and liver cancer. Fortunately, there is a vaccine that can protect you from hepatitis B. The hepatitis B vaccine is recommended for all infants and children and many groups of adults—however, anyone who wants to be protected can get it. While there isn't a vaccine for hepatitis C, there are very effective treatments that can cure the infection.

Approximately 1.25 million people in the United States have a chronic HBV infection.

Bacterial Vaginosis (BV)

Bacterial vaginosis (BV) is a condition in which the healthy bacteria in the vagina are replaced by different organisms. Symptoms include burning and itching around the vagina, white or gray discharge, and a strong fishy odor that is more noticeable after sex.

Some people question whether BV is an STD, but there is a link between BV and having a new sex partner or multiple sex partners. You can take antibiotics to get rid of BV, but it can show up again.

Bacterial vaginosis can increase the risk of HIV, pelvic inflammatory disease, and preterm birth (babies born too early).


This photo contains content that some people may find graphic or disturbing.


DermNet / CC BY-NC-ND

Chancroid is a disease caused by the bacterium Haemophilus ducreyi. Chancroid infections raise the risk of getting HIV. This STI isn't as common in the United States as it is in other parts of the world.

The ulcers caused by chancroid are often larger than those caused by syphilis. They can be more painful, too. Early on, it can be hard to tell these two infections apart.

Lymphogranuloma Venereum (LGV)

Lymphogranuloma venereum (LGV) is an STI caused by bacteria. At one time, LGV mostly affected people in developing countries. However, it is now on the rise worldwide.

In 2003, an LGV outbreak happened among men who have sex with men (MSM) in the Netherlands. Since then, it has been found in some groups of MSM across western Europe, North America, and Australia.

LGV is caused by a type of Chlamydia trachomatis. It can raise the risk of getting or spreading HIV.

Nongonoccocal Urethritis (NGU)

Nongonoccocal urethritis (NGU) causes urethritis. Urethritis is an inflammation of the tube that carries urine from your bladder to the outside of your body. NGU is inflammation caused by something other than gonorrhea. NGU can be caused by chlamydia and MG, however 50% of cases don't have an identifiable organism. Symptoms of NGU include burning when you urinate and discharge from the head of the penis. However, it is important to know that most people with NGU have no symptoms at all.

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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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Additional Reading

By Elizabeth Boskey, PhD
Elizabeth Boskey, PhD, MPH, CHES, is a social worker, adjunct lecturer, and expert writer in the field of sexually transmitted diseases.