Education, Epidemiology, Infectious Diseases, Wellness

The 10 Most Common Sexually Transmitted Diseases (STIs)

Author Chandana Balasubramanian , 12-Sep-2023

Sexually transmitted infections (STIs) are global public health concerns that demand serious attention. Despite advances in treatment, there are millions across the world who get infected each year.


Also known as STDs or sexually transmitted diseases, they can be spread from one person to another through sexual contact, including vaginal, anal, or oral sex and close skin-to-skin contact with an infected area.


If left untreated, STIs can cause serious health consequences. The impact of these infections extends far beyond each individual affected; they are a significant health concern for society as a whole. 


Have you ever wondered what the most common STIs are? From chlamydia to herpes, here are the 10 most common sexually transmitted infections – and what you need to know about them.



HIV (Human Immunodeficiency Virus) and Acquired Immunodeficiency Syndrome (AIDS)

An HIV epidemic blazed through the 1980s and 1990s, leaving devastation in its wake. At the time, the mention of HIV or AIDS often signaled severe illness and often, a death sentence.

  • According to the World Health Organization (WHO), HIV killed 40.4 million people.
  • WHO also reports that in 2022, 1.3 million people acquired HIV.

Thankfully, due to groundbreaking research and advanced therapies, people with HIV can now live long lives and manage their symptoms. 

What is HIV? 

HIV stands for the Human Immunodeficiency Virus. The virus spreads through the body fluids of an infected person, including semen, blood, vaginal fluids, and even breast milk. 

How does HIV infect the body?

Incubation period: Most people with HIV may experience symptoms similar to the flu within 2 to 6 weeks of contracting the HIV virus. After that, they may not have symptoms for years.  

The virus is relentless and attacks the immune system, weakening the body’s ability to fend off infections and diseases. So, apart from the effects of HIV itself, infected individuals are at the mercy of other infections and cancers as well.

How does HIV cause AIDS?

If left untreated, HIV can progress to AIDS, Acquired Immunodeficiency Syndrome. At this stage, the immune system is severely compromised. AIDS leaves individuals vulnerable to a variety of infections and cancers.

Is there a cure for HIV?

While there is no cure, antiretroviral therapy (ART) can manage the effects of HIV, allowing those affected to lead relatively healthy lives. 

Is there an AIDS vaccine?

The short answer is that no, there is no HIV vaccine. The biggest challenges include the fact that the HIV virus mutates rapidly, making it difficult to create an effective vaccine.

Also, the virus is quite wily and has many ways to evade our immune system. It can hide in long-lived reservoirs and has a host of other protective mechanisms that challenge vaccine development. 

However, there are over 20 HIV vaccine clinical trials underway, and hopefully, there may be a breakthrough. 

The best way to lower the risk of contracting HIV is preventive measures like PreP and safe sex practices including the use of condoms.

PrEP is pre-exposure prophylaxis – medication that lowers the risk of contracting HIV from either sex or injection drugs. PrEP has been highly effective at preventing HIV infections.


Human Papillomavirus (HPV)/Genital Warts

HPV is one of the most common STIs in the world:

  • According to the US Centers for Disease Control and Prevention, CDC, 85% of people will have contracted at least one type of HPV in their lifetime.
  • The biggest risk from HPV is cervical cancer. In fact, HPV causes more than 90% of all cervical cancers globally.


What is HPV?

The Human Papillomavirus (HPV) is actually a group of viruses that infect the skin and mucous membranes. There are more than a hundred different types of HPV, some of which can cause various health issues, including genital warts and certain cancers.

HPV is primarily spread through skin-to-skin contact, often during sex. It can also be transmitted through other forms of close contact like kissing or touching. 

Genital HPV is one of the most common STIs. 

How does HPV infect the body?

HPV infects the skin and mucous membranes, but most cause no symptoms, and often, the immune system is able to fight these infections off. However, high-risk versions can persist and lead to abnormal cell growth. 

High-risk HPVs can even lead to cervical, anal, and oropharyngeal cancers. 

Is there a cure for HPV? 

There is no cure for HPV, but most HPV infections can be cleared by our natural immune systems. There is no specific treatment for HPV, but therapy depends on the type of infection.

For example, if HPV causes genital warts, these warts may be treated through medication, cryotherapy, laser therapy, and other means. 

Is there an HPV vaccine?

The best way to prevent HPV infections is through vaccination.

HPV vaccines are recommended for both females and males before they become sexually active. These vaccines can protect against high-risk HPV infections including those that cause genital warts and cancers. 

There are several types of HPV vaccines available and the most well-known ones are Gardasil 9 (by Merck), and Cervarix (by GlaxoSmithKline). The HPV vaccines are often administered as a series of shots, over a few months.


3. Chlamydia

Chlamydia is often called a ‘silent infection’ because most infected people may not know they have it. 

  • According to WHO, in 2020, there were 128.5 million new cases of chlamydia around the globe in people aged 15 – 49. 
  • WHO recognizes chlamydia as an important public health issue and aims to reduce the global burden by 50% by 2030.
  • Young, sexually active people are most at risk of getting infected with chlamydia. 


What is chlamydia?

Chlamydia is a common STI caused by the bacteria chlamydia trachomatis. It affects both men and women and can lead to serious reproductive health problems if left untreated.  

Chlamydia is spread through sexual contact, including vaginal, anal, and oral sex with an infected person. It can also be transmitted from a mother to a child during childbirth. However, it cannot be transmitted by kissing, hugging, or touching. 

Most people who get chlamydia may not have symptoms. Even if symptoms appear, it may take weeks, months, or even years to appear. If people do not know they have an infection, there is a greater risk of spreading it. 

How does chlamydia infect the body?

Chlamydia infects the cells of the genital and urinary tract:

  • In females, it can cause inflammation of the cervix (cervicitis) and the urethra.
  • In males, it can cause inflammation in the urethra (urethritis).

Without treatment, the infection can spread to other reproductive organs, and there is a risk of causing more serious health problems. These include pelvic inflammatory disease (PID), infertility, or chronic pain.

Is there a cure for chlamydia?

The good news is that chlamydia can be cured, usually with antibiotics. The most commonly prescribed antibiotics for Chlamydia are azithromycin and doxycycline. 

On the plus side, due to more screenings for chlamydia, more cases are being detected. But there’s a catch. Since infections are detected early, antibiotics are often prescribed before the natural immune system has a chance to fight the infection. This may increase the risk of catching chlamydia again (reinfection).

Is there a chlamydia vaccine?

There is no vaccine to prevent chlamydia. However, research is underway to find one. For now, the best way is to practice safe sex, wear condoms, and practice hand hygiene.  



Gonorrhea is a common bacterial STI. People who are most at risk of getting gonorrhea are men who have sex with men (MSM), sex workers, transgender women, and young people in countries with a higher disease burden. 

  • WHO reports that in 2020, there were approximately 82.4 million new gonorrhea infections worldwide (among adults).
  • According to the CDC, gonorrhea is the second most commonly reported bacterial STI in the United States.


What is gonorrhea?

Gonorrhea is an STI caused by the bacteria neisseria gonorrhoeae. The disease mainly affects the genital tract but also infects the throat, rectum, and eyes. Like other STIs, if left untreated, it can lead to more severe health complications. 

Gonorrhea is primarily spread through sexual contact, including vaginal, anal, and oral sex. It can also be passed from an infected mother to her newborn during childbirth.

How does gonorrhea infect the body?

Incubation period: 1-14 days. Males may see symptoms within 2 to 5 days after infection but in females, symptoms may appear within 10 days.

Gonorrhea infects the mucous membranes of the reproductive and urinary tracts.

  • In females, it can cause cervicitis (inflammation of the cervix), pelvic inflammatory disease (PID), and other reproductive health issues.
  • In males, it can lead to urethritis (inflammation of the urethra).

The infection can also affect the throat and rectum.

Is there a cure for gonorrhea?

Yes, gonorrhea can be cured with the right antibiotics. However, lately, gonorrhea strains have developed antimicrobial resistance (AMR) to nearly every antibiotic used to treat the infection. This makes treatment more complicated. 

As a result, treatment often includes dual therapy with two different antibiotics. 

Is there a gonorrhea vaccine?

There is no vaccine for gonorrhea because the bacteria mutates quite often and develops resistance to antibiotics. In fact, the CDC estimates that there are 1.6 million new cases of gonorrhea each year with 50% of them resistant to at least one antibiotic!

Vaccine research is underway, but the best way to protect from gonorrhea is preventive measures. These include safe sex practices, regular screenings, and limiting the number of sexual partners. 



Syphilis is an STI caused by the bacteria treponema pallidum. The disease is spread primarily through direct contact with syphilis sores that can be found on the genitals, anus, lips, or mouth.

It can also be transmitted through blood transfusion or infected mothers to their babies during childhood.

  • WHO estimates that there were 7.1 million new adult syphilis infections in 2020.
  • Syphilis is known as ‘The Great Pretender’ because symptoms can mimic many other diseases, making it difficult to identify without specific antibody tests. 


How does syphilis infect the body?

Incubation period: The average time for syphilis symptoms to appear after getting infected is an average of 21 days but can range from 10 to 90 days.

Syphilis progresses through several stages:

  • Primary: Painless sores develop at the site of infection. 
  • Secondary: A rash and other symptoms may appear.
  • Latent: If untreated at the secondary stage, it may progress to the latent stage where there are no symptoms.
  • Tertiary: This is the most severe stage which may damage the heart, brain, and nervous system. 


Is there a cure for syphilis?

Syphilis can be cured if the proper treatment is administered in a timely manner. Antibiotics are the standard of care, and the type of medication depends on the stage of infection.

In the early stages, a long-acting shot of Benzathine penicillin G may be enough. In more severe stages, a longer course of treatment may be necessary. 

The Tuskegee Study controversy: There is a dark history associated with finding a cure for syphilis. In 1932, the US Public Health Service partnered with the Tuskegee Institute to study syphilis in 600 Black men, and almost 400 of them had syphilis.

The study is deeply controversial because even though penicillin became the preferred treatment for syphilis in the mid-1940s, the men in the study were not informed or provided treatment.

Also, the researchers did not get informed consent from their participants and told them they were being treated for “bad blood” instead.

Is there a syphilis vaccine?

There is no vaccine for syphilis. Preventive measures such as safe sex practices and the use of condoms are the best way to avoid getting infected. Regular screenings can also help detect infections early, if present. 


Hepatitis B

Hepatitis B is a sexually transmitted disease that has no cure. It is caused by the hepatitis B virus (HBV) and can cause short-term or chronic liver disease.   

  • WHO estimates that there are 1.9 million new hepatitis B infections each year.
  • The Hepatitis B vaccine is almost 100% effective in protecting against infection.


Hepatitis B can spread from infected mothers to their children at birth or through exposure to infected blood. HBV can also be transmitted through infected needles, tattooing, piercings, and exposure to body fluids like semen, vaginal fluids, and saliva.

How does hepatitis B infect the body?

Incubation period: Hepatitis B symptoms take an average of 90 days to appear but can take anywhere from 60 to 150 days.

HBV enters the body and targets the liver cells where it uses the cell’s machinery to replicate and create more virus particles. As its viral load increases, the body’s immune system begins to fight back. However, this response can cause inflammation in the liver (hepatitis). 

If the immune system cannot get rid of the virus completely, it can lead to a chronic infection where the virus can cause long-term liver damage. 

Is there a cure for hepatitis B?

Acute (short-term) hepatitis B can resolve in six months, and may not need treatment. However, chronic hepatitis B does not have a cure. It can be a lifelong issue, and in some instances, even fatal.

Is there a hepatitis B vaccine?

There is a highly effective hepatitis B vaccine that protects against both acute and chronic HBV infections and offers long-lasting immunity.

The vaccine is administered in a series of three doses. For healthcare workers and others at high risk of getting infected with HBV, booster shots are available.


Genital Herpes

Genital herpes is a common viral infection that is sexually transmitted and caused by the herpes simplex virus (HSV). There are two types of herpes simplex virus, HSV-1 and HSV-2. Both can cause genital herpes, but genital herpes by HSV-2 is the most common.

Genital herpes infections by HSV-1 are also on the rise because of changing sexual practices. The infection can be transmitted from the mouth of an infected person to the genitals.

Genital herpes is highly contagious, and HSV-2 can be transmitted through direct contact with the skin of infected individuals during sexual activity. The virus can spread even if there are no symptoms, making it harder to contain.

  • WHO estimates that 491 million people aged 15-49 have a herpes simplex virus type 2 infection.


There is a link between genital herpes and HIV. Herpes infections can cause sores or breaks in the skin, leaving an entryway for HIV. Plus, to fight herpes, more immune cells may accumulate near the genitals, making them soft targets for the HIV virus.

How does the herpes simplex virus HSV-2 infect the body?

Incubation period: The average is 4 days, but the range is 2 to 12 days after exposure. However, sometimes infected people may not notice symptoms even months or years after contracting the virus.

The HSV-2 virus enters the body through tiny breaks in the skin barrier. After that, it travels down nerve pathways to the nerves near the spinal cord and causes a lifelong infection. 

What’s more dangerous is that the virus can lay dormant in these nerve cells for a long period of time and reactivate at periodic intervals, leading to lifelong outbreaks. 

Is there a cure for genital herpes?

Unfortunately, there is no cure for genital herpes. Once someone is infected, the virus stays in the body for life.

Antiviral medication can help manage the symptoms of disease, and reduce the recurrence of outbreaks. The medicine also lowers the risk of transmitting the virus to sexual partners.

Is there a vaccine for genital herpes?

 There are no licensed vaccines against genital herpes. However, research is underway. 


Bacterial Vaginosis (BV)

Bacterial vaginosis (BV) is not a sexually transmitted infection but increases the risk of getting chlamydia and other STIs.

It is a condition where there is too much of a certain bacteria in the vagina. The exact cause of bacterial vaginosis is not known, but it is associated with lower lactobacilli bacteria in the vagina. 

What does a BV infection do to the body?

The overgrowth of certain bacteria may upset the delicate balance of bacteria in the vagina. This can lead to pH changes and altered vaginal discharge.

While half of women with BV do not have symptoms, symptoms include unusual vaginal discharge with a strong “fishy” smell, and it may be greyish-white and thicker in consistency.

Is there a cure for BV?

Usually, BV can resolve on its own. But common antibiotics can also help alleviate symptoms. 

Is there a vaccine for bacterial vaginosis?

No, there is no vaccine for bacterial vaginosis. 



Trichomoniasis is a common STI caused by a protozoan parasite called trichomonas vaginalis. It is commonly known as “trich,” and affects the genital and urinary tract in both males and females.

Trichomoniasis is usually transmitted through sexual contact, including vaginal, anal, and oral sex. The parasite is hardy and can survive in moist environments outside the body for a short time. This means it can be transmitted through shared wet towels or swimsuits. 

How does trichomoniasis infect the body?

The trichomonas vaginalis parasite attaches to the cells lining the genital and urinary tracts.

In females, it can cause inflammation, leading to a change in vaginal discharge to a thin, frothy, greenish-yellow or grey color. It may also have an unpleasant odor. This inflammation is often accompanied by itching and redness in the vaginal area. There may be a burning sensation during urination and pain during sex.

Males may have a clear or white discharge through their penis and discomfort or burning when urinating. 

Is there a cure for trichomonas?

Trichomoniasis is curable. Antibiotics like metronidazole are most commonly used. 

Is there a trichomonas vaccine? 

There is no vaccine developed for trichomoniasis. 


Pubic lice or 'crabs'

Pubic lice, commonly known as ‘crabs,’ are tiny parasites called pthirus pubis that infect the pubic area.

They are lumped in with STIs but are not really an infection or disease; they are more like an infestation. 

How do pubic lice affect the body?

Pubic lice are ectoparasites, which means they live outside the body and feed on blood. They attach their eggs to the base of the hair shafts and feed on the host’s blood. They can cause itching and discomfort in the area.

Although they are called pubic lice, they can infest armpits, chest, abdomen, and even beards. 

What is the treatment for pubic lice?

Over-the-counter medicated shampoos, creams, or lotions with insecticides can help get rid of pubic lice



STIs are a major public health concern, and it is important to increase awareness about their prevention, transmission, and treatment.

Sexually transmitted infections can be serious and have long-lasting health effects, on people who are infected as well as our entire global community. While there are vaccines to help prevent some of them, other preventive measures include safe sex practices, the use of condoms, and regular screenings for early detection. 


The GIDEON difference

GIDEON is one of the most well-known and comprehensive global databases for infectious diseases. Data is refreshed daily, and the GIDEON API allows medical professionals and researchers access to a continuous stream of data. Whether your research involves quantifying data, learning about specific microbes, or testing out differential diagnosis tools, GIDEON has you covered with a program that has met standards for excellence.

Get the latest on infectious diseases on the GIDEON platform.


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Chandana Balasubramanian

Chandana Balasubramanian is an experienced healthcare executive who writes on the intersection of healthcare and technology. She is the President of Global Insight Advisory Network, and has a Masters degree in Biomedical Engineering from the University of Wisconsin-Madison, USA.

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