What Are Sexually Transmitted Diseases?

Sexually transmitted diseases, also known as STDs, are illnesses that are transmitted through sexual contact. That usually means vaginal, oral, or anal sex, though certain STDs can also be transmitted through intimate skin-to-skin contact. Bacteria, viruses, and parasites cause STDs, and they can infect anyone. Bacteria, viruses, and parasites cause STDs, and they can infect anyone--male, female, nonbinary, intersex, cisgender, transgender, gay, straight, bisexual, pansexual, etc. If you’re sexually active, you could be at risk of contracting an STD. What’s more, many STDs don’t cause any symptoms (or only mild symptoms), so you could be infected and not know it.

The good news is that all STDs are treatable with medicine, and many can be completely cured. In addition, these diseases are preventable, and you can take steps to protect yourself and your partners.

The first step in reducing the risk of spreading an STD is finding out if you have an STD, which is why getting tested is so important.

Now, let’s take a closer look at some of the more common STDs


Chlamydia is a bacterial infection that is transmitted through unprotected vaginal, anal, and oral sex. Nearly four million Americans contracted chlamydia in 2018, and it is the most frequently reported sexually transmitted infection in the United States. It is most common among females between the ages of 15 and 24.

Chlamydia — Rates of Reported Cases by Age Group and Sex, United States, 2019

*Per 100,000
Source: CDC

Luckily, chlamydia can be cured with antibiotics. However, the disease can cause serious damage to a woman’s reproductive system if it is left untreated, potentially leading to infertility or causing fatal ectopic pregnancies.


Sometimes known as “the clap,” gonorrhea is a common bacterial STD. The CDC estimates that there were 1.6 million new infections in 2018, with more than half occurring in people ages 15-24.

Gonorrhea — Rates of Reported Cases by Sex, United States, 2010–2019

*Per 100,000
Source: CDC

People often show no symptoms when they have gonorrhea. When there are symptoms, they may include:

  • Painful urination
  • Discharge from the penis or vagina
  • Pain or swelling in one testicle
  • Vaginal bleeding between periods

A pregnant woman can pass gonorrhea onto her baby during delivery, which can cause blindness or even a fatal blood infection.

Fortunately, gonorrhea can be cured with proper treatment.


Hepatitis is an inflammation of the liver that is often caused by a viral infection. Three types of the virus—hepatitis A, B, and C—can be transmitted via sexual contact, though hepatitis B is the most likely to be spread through sex. Fortunately, rates of hepatitis B infection have been declining, which is attributed to more young people being vaccinated against that virus type.

Rates of Reported Acute Hepatitis B Virus Infection, by Age Group — United States, 2004–2019

Source: CDC

Vaccines are available and recommended to protect against hepatitis A and B. There is currently no vaccine against hepatitis C, though there are treatments available if the infection becomes chronic.


Herpes is a very common STD in the United States. It is usually divided into two types: genital and oral. According to CDC estimates, there were 572,000 new genital herpes infections among adults aged 14 to 49 in the United States in 2018.

Prevalence of Herpes Simplex Virus Type 1 in the U.S. in 2015-2016, by Age

Source: Statista

The most common symptom of genital and oral herpes is sores, though it is possible to have and transmit the disease without them. Treatments are available for herpes, but there is no cure; it stays with you for life when you are infected with the virus.


The human immunodeficiency virus, better known as HIV, attacks the body’s immune system. If untreated, the virus can cause acquired immunodeficiency syndrome or AIDS According to the CDC, approximately 1,189,700 million people aged 13 and older had HIV in the United States at the end of 2019.

Within two to four weeks of infection, some—but not all—people experience the following flu-like symptoms:

  • Fever
  • Chills
  • Rash
  • Night sweats
  • Muscle aches
  • Sore throat
  • Fatigue
  • Swollen lymph nodes
  • Mouth ulcers

Source: CDC


Syphilis is a sexually transmitted disease that can be cured, though it can cause serious health issues if left untreated. There are four stages of the disease—primary, secondary, latent, and tertiary—each with different symptoms. In the primary stage, syphilis leads to genital sores called chancres. These sores are often painless and may not even be noticeable, but contact with an infected person’s chancres can spread the disease. Syphilis can also be transmitted from a pregnant woman to her baby. This potentially fatal condition is called congenital syphilis and reported cases have been increasing since 2015.

Congenital Syphilis — Reported Cases by Vital Status and Clinical Signs and Symptoms* of Infection, United States, 2015–2019

*Infants with signs/symptoms of congenital syphilis have documentation of at least one of the following: long bone changes consistent with congenital syphilis, snuffles, condyloma lata, syphilitic skin rash, pseudoparalysis, hepatosplenomegaly, edema, jaundice due to syphilitic hepatitis, reactive CSF-VDRL, elevated CSF WBC or protein, or evidence of direct detection of T. Pallidum.

NOTE: Of the 5,269 congenital syphilis cases reported during 2015–2019, 22 (0.4%) did not have sufficient information to be categorized.

Source: CDC

When syphilis spreads to the brain and nervous system—a condition called neurosyphilis —it can cause paralysis, numbness, and dementia. Syphilis is treatable and curable with antibiotics, but treatment may not undo the damage that has already been done while someone was infected.


Also known as “trich,” trichomoniasis is a common STD that’s caused by a parasite. The CDC estimates that more than two million people were infected in 2018. Roughly 30% of those people show symptoms, which include itching, burning, and discharge. Unlike many STDs, trichomoniasis is more common in older women.

Prevalence of STDs Among Women

In the United States, there were an estimated 2.6 million trichomoniasis infections in 2018. Trichomoniasis can increase the risk of getting or spreading HIV, and pregnant women with the infection are more likely to have their babies too early (preterm delivery) and with a low birth weight.

Source: CDC

If you are diagnosed with trichomoniasis, you can be cured with prescribed medication. To prevent reinfection, your sexual partner(s) should get treated as well.

Now that you know the basics of these common STDs, you may be curious if you are infected with any. To find out, click here and learn more about various tests you can request from Enzo.

Reference to specific commercial products, manufacturers, companies, or trademarks does not constitute its endorsement or recommendation by the U.S. Government, Department of Health and Human Services, or Centers for Disease Control and Prevention; This material is otherwise available on the agency website for no charge.