Facts About 6 Common STIs

Mackenzie Flynn and Kristine Chin, National Center for Health Research

Sexually transmitted infections (STIs) are infections or diseases passed from one person to another through sexual activity. Although the terms sexually transmitted diseases (STDs) and STIs are often used interchangeably, STI is becoming the more common description because many individuals do not experience any symptoms that would typically indicate a disease.

Each year there are roughly 20 million new cases of STIs in the United States.[1] While some STIs are not obvious, others can cause a wide variety of symptoms, ranging from rashes to liver failure. Here is a list of the most common STIs, their symptoms, the treatment options available, and some ways to prevent infection in the first place.



Chlamydia is one of the most common bacterial STIs. It can cause inflammation in the urethra, rectum, and anus of men and women. Women can also experience swelling of the cervix (Figure 2). Most people with chlamydia do not have any symptoms, but some infected individuals experience a burning feeling when they urinate or have an abnormal discharge from the vagina or penis. The infection can cause chronic pelvic pain. It can also eventually cause pelvic inflammatory disease (PID) or block the fallopian tubes, either of which can cause permanent infertility. Chlamydia can also increase the chances of an ectopic pregnancy, which is fatal to the fetus and potentially life threatening to the life of the mother.[2]

Chlamydia is contagious and is typically spread during oral, vaginal, or anal sex as well as from mother to baby during childbirth. Antibiotics can cure chlamydia, but they cannot reverse the damage that the bacteria have already caused to the body, such as scarring.[3]


Gonorrhea, aka “The Clap,” is caused by bacteria that infects mucous membranes, affecting the urethra, rectum or throat in both males and females. It can also affect the uterus, fallopian tubes, and cervix in females (Figure 2).

The infection is spread during oral, vaginal, or anal sex and from mother to baby during childbirth. Gonorrhea does not usually cause symptoms, but some patients experience a painful, burning sensation during urination and/or have an unusual discharge. It can also cause vaginal bleeding between periods, abdominal pain, and pelvic pain in females. Gonorrhea, like chlamydia, can cause pelvic inflammatory disease (PID).[4]

Antibiotics can successfully treat the infection but will not reverse any damage that the bacteria caused before treatment.[5]

Hepatitis B (HBV)

Hepatitis B is a virus that infects the liver. The virus is passed through body fluids, such as blood and semen. The infection is spread through sex, sharing needles, or from mother to child during childbirth.

Many individuals with HBV never have symptoms. Those who do may experience fever, fatigue, vomiting, dark urine, and jaundice—all of which could be easily confused for other illnesses. This happens if the infection is not treated or if the treatment is not effective and the virus remains in the body for longer than 6 months.[6]

Children are typically vaccinated for HBV at age 11-15. Vaccinations can protect both men and women from HBV. There is no treatment for acute or chronic HBV, but it usually goes away on its own. It is recommended that a person with an acute infection gets enough fluids and nutrition. If an acute infection becomes chronic, treatments are available that reduce the amount of virus in the blood and the risk of developing liver disease. Such treatments include antiviral medications, interferon alfa-2b injections, and a liver transplant in serious cases.[7] If someone is diagnosed with chronic HBV, they should see a doctor to develop a treatment plan.


Genital herpes is an STI caused by two viruses, called Type 1 and Type 2.  Both kinds of herpes can infect the genital area and the mouth. Type 1 usually causes oral herpes, while Type 2 usually causes genital herpes. The herpes viruses can be inactive for weeks, months, or even years, but they can keep coming back as an active infection throughout life. It is possible for both types of herpes to infect individuals at the same time.

Even if an infected individual has no symptoms, they can still infect others.[1] Symptoms include painful bumps and blisters or sores at the site of infection (mouth, genitals, or anus). Herpes is passed through direct skin-to-skin contact, often during kissing, sex, and contact with the genital area or fluids of someone who is infected.

There is currently no cure for herpes. However, antiviral drugs can shorten outbreaks, decrease symptoms, and make the virus less contagious to others.[8]

Human Papillomavirus (HPV) Infection

HPV is the most common sexually transmitted infection in the United States. HPV is a virus passed through skin-to-skin contact during vaginal and anal sex, and sometimes through oral sex. Most individuals with HPV don’t have any symptoms, which is why it often spreads when a person has more than one sexual partner. Some individuals get warts on the genitals or surrounding skin, which can go away and come back.

In most cases, HPV goes away on its own. But when it does not go away, it can result in genital warts and conditions such as cancer. HPV can cause cervical and other cancers such as cancer of the vulva, vagina, penis, anus and oropharynx (back of the throat).[9]

There is no cure for HPV, but The HPV vaccine helps protect you against certain types of HPV that can lead to cancer or genital warts. Children are typically vaccinated for HPV at 11 or 12 years of age, but vaccinations can be given anywhere between 9 to 26 years of age.


Syphilis is a bacterial infection that can infect the lips, mouth, genital area, or anus.[10] It is mainly spread by vaginal and anal sex, and sometimes through oral sex. Syphilis has four stages—primary, secondary, latent, and tertiary.

Primary syphilis causes a small sore (a chancre) at the infected spot. There is usually only one sore, but some people have more than one. The sores appear between 3 weeks and 3 months after infection, and typically go away on their own within 3 to 6 weeks.

Secondary syphilis usually begins several weeks after that sore heals. During this stage, rashes occur on the palms of one’s hands, soles of the feet, or other parts of the body.[11] The rash could either disappear completely in a few weeks or come and go for as long as 2 years. These rashes often lead individuals to seek care, become diagnosed, and get treated. However, if an infected person has not received treatment, the infection can progress into latent or tertiary syphilis.

Latent syphilis is when there are no symptoms for months or years (or a latent period), but individuals still need to get treatment. The disease will either never come back or move onto the tertiary stage.

When the infection returns after a latency period of no symptoms, it is called tertiary syphilis. This can result in damage to the brain, nerves, eyes, heart, liver, bones and joints. This can lead to neurosyphilis, which can cause impaired balance, chronic pain, lack of muscle coordination, and nausea.[12]

If treated at its early stages, syphilis can be cured by a single penicillin injection. Latent syphilis can potentially be treated with multiple injections of penicillin every week. The number of weeks for treatment varies because the bacteria can become dormant at different times for different people.

People who have been cured of syphilis are still at risk of getting a new syphilis infection if they are exposed again.

Diagnosis and Prevention

A physician can diagnose most of these STIs with either a urine test or a swab test of the affected areas. In some cases of HBV, doctors may want a liver sample to determine how much liver damage there is.

Getting information about STIs is more important than ever, since there are more than 1 million sexually transmitted infections acquired every day worldwide.[13] The most effective way to avoid getting STIs is abstinence. Vaccines are also available to help prevent HBV and another viral STI, Human papillomavirus (HPV) infection. When used correctly and consistently, male and female condoms and dental dams provide a physical barrier that can protect individuals from getting an STI. However, some STIs, such as herpes, can spread if a condom/dental dam does not cover blisters.

Having only one sex partner or a small number of sex partners also decreases one’s chances of getting STIs.[14] Even so, individuals should get tested regularly. If someone is diagnosed with an STI, they should tell their partner or partners to help prevent spreading the disease to others.


All articles are reviewed and approved by Dr. Diana Zuckerman and other senior staff.

The National Center for Health Research is a nonprofit, nonpartisan research, education and advocacy organization that analyzes and explains the latest medical research and speaks out on policies and programs. We do not accept funding from pharmaceutical companies or medical device manufacturersFind out how you can support us here.

  1. Sexually Transmitted Diseases – Adolescents and Young Adults (2017 December 7). Retrieved November 1, 2019 from https://www.cdc.gov/std/life-stages-populations/adolescents-youngadults.htm
  2. Chlamydia- CDC Fact Sheet (Detailed) (2016 October 4). Retrieved November 1, 2019 from https://www.cdc.gov/std/chlamydia/stdfact-chlamydia-detailed.htm
  3. ePublications Chlamydia (2019 April 1). Retrieved November 1, 2019 from https://www.womenshealth.gov/a-z-topics/chlamydia
  4. Pelvic Inflammatory Disease (PID) – CDC Fact Sheet (2017 January 25). Retrieved November 1, 2019 from https://www.cdc.gov/std/pid/stdfact-pid-detailed.htm
  5. ePublications: Gonorrhea (2019 April 1). Retrieved November 1, 2019 from http://www.womenshealth.gov/publications/our-publications/fact-sheet/gonorrhea.html
  6. Hepatitis B FAQs for Health Professionals (2019 Oct 25). Retrieved on November 1, 2019, from http://www.cdc.gov/hepatitis/hbv/hbvfaq.htm#treatment
  7. Treatment Options (2019). Retrieved November 1, 2019 from https://www.hepb.org/treatment-and-management/treatment/
  8. WHO Herpes simplex virus (2017 January 31). Retrieved November 1, 2019 from https://www.who.int/news-room/fact-sheets/detail/herpes-simplex-virus
  9. Cancers Associated with Human Papillomavirus (HPV) (2018 August 22). Retrieved November 6, 2019 from https://www.cdc.gov/cancer/hpv/basic_info/cancers.htm
  10. Syphilis – CDC Fact Sheet (Detailed) (2017 January 30). Retrieved November 1, 2019 from http://www.cdc.gov/std/syphilis/stdfact-syphilis-detailed.htm
  11. Syphilis: What Is It? (2019 March). Retrieved on November 1, 2019 from https://www.health.harvard.edu/a_to_z/syphilis-a-to-z
  12. NINDS Neurosyphilis Information Page (2019 March 27). Retrieved November 1, 2019, from https://www.ninds.nih.gov/Disorders/All-Disorders/Neurosyphilis-Information-Page
  13. Sexually Transmitted Infections (STIs) (2019 June 14). Retrieved November 1, 2019 from https://www.who.int/news-room/fact-sheets/detail/sexually-transmitted-infections-(stis)
  14. How You Can Prevent Sexually Transmitted Diseases (2016 January 21). Retrieved November 1, 2019 from http://www.cdc.gov/std/prevention/