Also Known As
Sexually Transmitted Infections
Venereal Diseases
This article was last reviewed on
This article waslast modified on August 10, 2020.
What are sexually transmitted diseases?

Sexually transmitted diseases (STDs), also called sexually transmitted infections (STIs) or venereal diseases, are infections caused by organisms that can be transmitted from one person to another through sexual activity and intimate contact. The U.S. Centers for Disease Control and Prevention (CDC) estimates that there are almost 20 million new STD cases each year in the U.S. Half of cases occur in young people between the ages of 15 and 24 years.

Since many STDs have few or no symptoms, it is possible for a person to have an infection and to infect others without either of them knowing it. For this reason, screening for these infections is important to ensure early detection and prompt treatment. Tests for STDs are recommended as part of routine health screens for sexually active teens and young adults as well as older adults who may be at risk.

Untreated STDs have significant long-term consequences. They can lead to sterility in both sexes. In women, STDs can result in pelvic inflammatory disease (PID), which increases the risk of infertility and ectopic pregnancies. One STD in particular, HPV, can increase risk of cervical cancer in women. In addition, women who are pregnant or planning a pregnancy should be aware that untreated STDs can cause complications for their newborn. Screening tests for several of these STDs are now part of routine prenatal care.

Accordion Title
About Sexually Transmitted Diseases
  • Types

    The most common STDs are listed below:

    • Chlamydia. According to the CDC, chlamydia is the most frequently reported bacterial STD in the U.S. In 2014, roughly 1.4 million cases of chlamydia represented the highest number of annual cases of any condition ever reported to the CDC. Infection is caused by the bacterium Chlamydia trachomatis and is often called "the silent epidemic" because infections are common yet many people do not realize that they are infected. It is easily cured with antibiotics but can have serious health consequences if left untreated, including PID.
    • Gonorrhea. Neisseria gonorrhoeae causes the bacterial STD gonorrhea. It may not cause symptoms, especially in women, but can lead to PID, infertility, and other complications if not treated with antibiotics.
    • Syphilis. Syphilis is another bacterial infection that can be easily missed. The first symptom is a painless chancre (an ulceration of the skin) at the site of exposure that will disappear on its own, giving the impression that the infection has resolved when, in fact, the infection persists for a period of time without symptoms. Syphilis can be treated with antibiotics. However, if left untreated, the disease can spread throughout the body over the course of many years and cause considerable organ damage.
    • Trichomonas. Trichomonas vaginalis is a microscopic parasite that causes trichomoniasis, a common STD, especially among sexually active young women. It can be treated with a single dose of antibiotic medication.
    • Human papillomavirus (HPV). One of the most common STDs in the United States, this virus can infect the genital area as well as the mouth and throat. There are over 100 types of HPV. Low-risk types can cause genital warts (condyloma) while high-risk types can lead to cervical cancer and other genital cancers. Early detection can reduce the risk of cancer. Vaccines are available that protect against certain types of HPV. 
    • Genital herpes. The herpes simplex virus (HSV) causes recurrent, periodic outbreaks of sores in the genital region and remains in an infected person's body for life. However, there are anti-viral therapies available that can shorten the duration of symptoms.
    • Hepatitis B and Hepatitis C. These are viral infections that can cause liver inflammation. They can be transmitted through sexual contact although hepatitis C is spread more often through sharing of contaminated needles or other equipment used to inject drugs. Both viruses can cause acute forms of the disease that usually result in a few mild symptoms or no symptoms, but they can also progress to a chronic form that causes severe and/or lasting liver damage. Treatment of chronic hepatitis with antiviral medications is available. There is a vaccine to prevent hepatitis B, but currently no vaccine is available for hepatitis C, although one is in the early stages of testing. Read more on these types of viral hepatitis.
    • Human Immunodeficiency Virus (HIV). HIV is the virus that causes AIDS. It attacks and destroys certain white blood cells (T-helper lymphocytes) that are an important part of the immune system. As the number of these cells is reduced, the ability of the body to fight off infections also decreases. Although there is no cure, early detection allows for treatment with anti-retroviral therapies (ART) that can help to prolong life.
  • Tests
  • Treatment

    For any sexually transmitted disease, if you are infected, you should inform your sexual partner(s) so that they may be tested and treated as well. In some states, public health workers will contact those with recently reported gonorrhea, chlamydia, or syphilis infections (the three nationally reported STDs) to be sure that they were treated and to get the names of their sexual partner(s) to notify them to get tested and treated as well.

    Correct use of latex condoms greatly reduces the chances of becoming infected or spreading STDs, but it does not completely eliminate the risk. For more on how to reduce your risk and prevention tips, visit the American Sexual Health Association web site.

View Sources

Sources Used in Current Review

CDC Fact Sheet. Reported STDs in the United States. 2014 National Data for Chlamydia, Gonorrhea, and Syphilis. Available online at Accessed November 2015.

MedlinePlus. Sexually Transmitted Diseases. Available online at Accessed November 2015.

MedlinePlus. HPV. Available online at Accessed November 2015.

American Sexual Health Association. Hepatitis. Available online at Accessed November 2015.

American Sexual Health Association. Hepatitis C. Available online at Accessed November 2015.

Sources Used in Previous Reviews

National Institute of Allergy and Infectious Diseases (NIAID, NIH). Sexually Transmitted Infections. Available online at with additional information (Key points about STIs in the United States) at Accessed February 12, 2009.

Barclay, Laurie. CDC Issues Annual Report on Sexually Transmitted Diseases. Medscape Today. Available online at Accessed February 2009.

CDC – NPIN. STDs – Today. Available online at Accessed February 2012.

Information on GARDASIL. Available online at Accessed February 2012.

CDC. Sexually Transmitted Diseases (STDs), Trichomoniasis - CDC Fact Sheet. Available online at Accessed February 2012.

Sinnema, J. University of Alberta researchers move closer to hepatitis C vaccine. Postmedia News. February 15, 2012. Available online at Accessed February 2012.