The 10 Most Common STIs: What You Need to Know for Better Health

Sexually transmitted infections (STIs) are more common than most people realize, yet conversations about them often happen in whispers, if at all. That silence contributes to their continued spread. According to the latest CDC data, over 2.4 million cases of STIs were diagnosed in the United States alone, including more than 1.6 million cases of chlamydia, 600,000 cases of gonorrhea, and 209,000 cases of syphilis. Almost half (48.2%) of these cases occurred among young adults aged 15-24 years.

The reality is that most sexually active people will encounter an STI at some point in their lives. Understanding what these infections are, how they spread, and how to recognize and treat them is crucial for your health and the health of your partners.

In this comprehensive guide, we'll explore the ten most common STIs, their symptoms, testing options, and how to protect yourself and your partners.

1. Chlamydia: The Silent Infection

What It Is: Chlamydia is a bacterial infection caused by Chlamydia trachomatis that affects the genital tract, urinary tract, and sometimes the eyes.

How Common: Chlamydia is the most commonly reported STI in the United States. In 2023, over 1.6 million cases were reported, though the actual number is likely much higher since many cases go undiagnosed. Globally, the WHO estimated 129 million chlamydia infections in 2020.

Symptoms: Most people with chlamydia (about 70-80%) have no symptoms at all, which is why it's often called "the silent infection." When symptoms do appear, they typically include:

• Abnormal vaginal discharge
• Burning sensation during urination
• Pain or discomfort during sex
• Lower abdominal pain (particularly in women)
• Testicular pain or swelling (in men)

Testing: A simple urine test or swab can detect chlamydia. The CDC recommends annual screening for all sexually active women under 25 and older women with risk factors.

Treatment: Chlamydia can be treated and cured with antibiotics. However, if left untreated, it can lead to serious health problems, including pelvic inflammatory disease (PID) and infertility in women.

2. Gonorrhea: The Increasingly Resistant Threat

What It Is: Gonorrhea is caused by the bacterium Neisseria gonorrhoeae, which can infect the genitals, rectum, throat, and eyes.

How Common: Gonorrhea is the second most commonly reported STI in the U.S., with over 600,000 cases reported in 2023. While overall rates decreased by 7.7% from 2022 to 2023 with the most pronounced decreases among women (14.1% decrease), the infection remains a serious concern.

Symptoms: Like chlamydia, many people with gonorrhea don't have symptoms. When symptoms occur, they can include:

• Yellow or green discharge from the penis or vagina
• Painful or burning urination
• Sore throat (from oral sex)
• Rectal pain, discharge, or bleeding (from anal sex)
• Increased vaginal bleeding between periods

Testing: Gonorrhea can be detected through urine tests or swabs from the infected area (genitals, throat, or rectum).

Treatment: While gonorrhea is treatable with antibiotics, the bacteria has become increasingly resistant to many drugs. This growing antibiotic resistance makes gonorrhea a more significant public health threat than ever before.

3. Human Papillomavirus (HPV): The Most Widespread STI

What It Is: HPV is a group of more than 150 related viruses, some of which can cause genital warts while others can lead to various cancers, including cervical, anal, and throat cancers.

How Common: HPV is thought to be the most common STI overall, with studies suggesting around three-quarters of sexually active people acquire this incurable viral STI at some point in their live.

Symptoms: Most people with HPV never develop symptoms or health problems. Some types cause genital warts, while other high-risk types can lead to cancer over time.

Testing: There's no routine test for HPV in men. For women, HPV testing is often done alongside Pap tests during cervical cancer screening.

Prevention and Treatment: There's a vaccine to prevent HPV and genital warts. Healthcare providers advise children ages 11 to 12 to receive it because it's most effective before becoming sexually active. While there's no cure for HPV, warts can be treated, and regular screening can detect cervical cell changes before they become cancerous.

4. Genital Herpes: The Lifelong Companion

What It Is: Genital herpes is caused by two types of the herpes simplex virus: HSV-1 (which typically causes oral herpes but can cause genital herpes through oral sex) and HSV-2 (which primarily causes genital herpes).

How Common: Genital herpes affects about one out of every six people in the U.S. aged 14 to 49. Worldwide, more than 490 million people were estimated to be living with genital herpes in 2016.

Symptoms: Many people with herpes never have symptoms or have very mild symptoms that go unnoticed. When symptoms do occur, they typically include:

• Painful blisters or sores on the genitals, rectum, buttocks, or thighs
• Itching or tingling in the genital area
• Flu-like symptoms during the first outbreak (fever, body aches, swollen lymph nodes)

Testing: Blood tests can detect herpes antibodies, or a healthcare provider can take a sample from an active sore.

Treatment: While there's no cure for herpes, antiviral medications can reduce the frequency and severity of outbreaks and lower the risk of transmission to partners.

5. Trichomoniasis: The Underrecognized Parasite

What It Is: Trichomoniasis (often called "trich") is caused by a parasite that infects the genital tract.

How Common: Trichomonas is the most common STI globally, with 156 million new cases yearly, yet it often goes undiagnosed.

Symptoms: About 70% of infected people don't have any symptoms. When symptoms do occur, they can include:

• Abnormal vaginal discharge with a strong odor
• Genital itching or irritation
• Burning during urination
• Discomfort during sex

Testing: Trichomoniasis can be diagnosed with a laboratory test of a genital swab or urine sample.

Treatment: Trichomoniasis is easily cured with a single dose of prescribed antibiotic medication, typically metronidazole or tinidazole.

6. Syphilis: The Great Imitator

What It Is: Syphilis is a bacterial infection caused by Treponema pallidum that develops in stages and can affect multiple body systems.

How Common: Syphilis rates have been increasing alarmingly in recent years. In 2023, 209,253 cases of syphilis were reported, the highest number since 1950.

Symptoms: Syphilis is known as "the great imitator" because its symptoms resemble many other diseases. The stages include:

• Primary stage: A painless sore or chancre at the site of infection
• Secondary stage: Skin rash, mucous membrane lesions, fever, sore throat, and swollen lymph nodes
• Latent stage: No visible symptoms
• Tertiary stage: Severe damage to organs, including the brain, nerves, eyes, heart, and other tissues

Testing: Blood tests can detect antibodies that the body creates to fight the infection.

Treatment: Syphilis can be cured with the right antibiotics, typically penicillin. However, treatment cannot undo damage already done by the infection.

7. HIV: The Immune System Attacker

What It Is: Human Immunodeficiency Virus (HIV) attacks the body's immune system, specifically CD4 cells (T cells), reducing the body's ability to fight off infections and disease.

How Common: Worldwide, about 38 million people are living with HIV. In the United States, approximately 1.2 million people are HIV-positive, with about 13% unaware of their status.

Symptoms: Many people experience no symptoms when first infected with HIV. Others may develop flu-like symptoms within 2-4 weeks, including:

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

Testing: HIV tests look for antibodies, antigens, or the virus itself in blood or oral fluid. Regular testing is recommended for those at risk.

Treatment: While there's no cure for HIV, antiretroviral therapy (ART) can control the virus effectively. People with HIV who take ART as prescribed can live long, healthy lives and prevent transmitting the virus to their sexual partners.

8. Mycoplasma Genitalium: The Emerging Concern

What It Is: Mycoplasma genitalium (MG) is a bacterial infection that can cause inflammation of the urethra, cervix, and reproductive organs.

How Common: In 2022, between 640,000 and 1.6 million new MG infections were thought to have occurred in the U.S. 

Symptoms: Many people with MG have no symptoms. When symptoms do occur, they can include:

• Painful urination
• Abnormal discharge
• Painful intercourse for women
• Pain and swelling of the testicles for men

Testing: Specialized nucleic acid amplification tests (NAATs) can detect MG.

Treatment: MG can be treated with antibiotics, but resistance to common treatments is increasing. Healthcare providers may need to adjust treatment if initial therapy fails.

9. Hepatitis B: The Liver Attacker

What It Is: Hepatitis B is a viral infection that attacks the liver and can cause both acute and chronic disease.

How Common: Updated WHO estimates indicate that 254 million people were living with hepatitis B in 2022.

Symptoms: Many people with acute hepatitis B don't experience symptoms. When symptoms appear, they can include:

• Fatigue
• Nausea and vomiting
• Abdominal pain
• Jaundice (yellowing of the skin and eyes)
• Dark urine
• Light-colored stools

Testing: Blood tests can detect hepatitis B virus infections.

Prevention and Treatment: Safe and highly effective vaccines are available for hepatitis B, representing a major advance in STI prevention. Antiviral medications can help manage chronic hepatitis B,

10. Pubic Lice ("Crabs"): The Unwelcome Visitors

What It Is: Pubic lice (Pthirus pubis), commonly known as "crabs," are tiny parasitic insects that attach to pubic hair and other coarse body hair, including chest hair, eyebrows, and eyelashes.

How Common: While exact numbers are hard to determine, pubic lice affect approximately 3 million people in the United States each year. They're one of the most easily transmissible STIs.

Symptoms: The primary symptoms of pubic lice include:

• Intense itching in the genital area
• Visible lice or eggs (nits) at the base of pubic hair
• Small blue or gray spots on the skin (caused by lice bites)
• Irritation and inflammation in the affected area

Testing: A healthcare provider can diagnose pubic lice through a visual examination, sometimes using a magnifying glass to identify the lice or their eggs.

Treatment: Pubic lice are treated with over-the-counter or prescription medications specifically designed to kill lice and their eggs. Treatment usually involves washing the affected area with a medicated shampoo or lotion. Clothing, bedding, and towels should be washed in hot water to prevent reinfestation.

Protecting Yourself: Prevention Strategies That Work

While the statistics may seem daunting, there are effective ways to protect yourself from STIs:

1. Practice safer sex: Use condoms or dental dams consistently and correctly. While not 100% effective against all STIs (particularly those spread through skin-to-skin contact), condoms have had a significant impact on preventing STIs, including averting approximately 117 million new HIV infections since 1990.
2. Get tested regularly: Many STIs don't cause symptoms, so regular screening is essential, especially if you have new or multiple partners. Knowing your status empowers you to get proper treatment and prevent spreading infections to others.
3. Communicate openly: Nearly 95% of young people surveyed stated they would share their STI results with their partners, recognizing the importance of disclosure to prevent spread. Have honest conversations with partners about sexual health before becoming intimate.
4. Get vaccinated: Vaccines are available for HPV and hepatitis B, offering powerful protection against these infections and their long-term consequences.
5. Consider PrEP for HIV prevention: If you're at high risk for HIV, pre-exposure prophylaxis (PrEP) can significantly reduce your risk of infection.
6. Limit your number of sexual partners: Fewer partners means fewer opportunities for exposure to STIs.

The Importance of Testing and Treatment

Many people avoid getting tested for STIs due to embarrassment, fear, or the misconception that they would definitely know if they had an infection. However, as we've seen, many STIs cause no symptoms at all, especially in the early stages.

Regular testing is the only way to know for sure if you have an STI. If you do test positive, remember:

• Most STIs are easily treatable, especially when caught early
• Prompt treatment prevents complications and reduces transmission to partners
• Getting treated is an act of care for yourself and others
• Having an STI is incredibly common and isn't a reflection of your worth or character

How Twentyeight Health Can Help

At Twentyeight Health, we're committed to making STI testing and treatment accessible, affordable, and judgment-free. Our services include:

• Convenient online consultations: Skip the waiting room and connect with our healthcare providers from the comfort of your home.
• Comprehensive STI testing: We offer testing for all common STIs, with clear guidance on which tests may be right for your situation.
• Discreet treatment options: If you test positive for an STI, our providers can prescribe appropriate medications that are delivered right to your door in unmarked packaging.
• Ongoing support: Our healthcare team is available to answer your questions and provide support throughout your treatment.
• Insurance and Medicaid accepted: We accept more Medicaid plans than any other healthcare platform, along with most major insurance carriers, to ensure care is affordable for everyone.
• Self-pay options: Don't have insurance? Our Standard Care Plan provides unlimited provider messaging and affordable medication options starting at just $12.99/month.

Your sexual health is an important part of your overall wellbeing, and you deserve care that's accessible, affordable, and free from judgment or stigma. Whether you're experiencing symptoms, want routine screening, or just have questions about sexual health, Twentyeight Health is here to help you take control of your health journey.

Ready to take the first step? Visit twentyeighthealth.com today to schedule an online consultation or STI screening with one of our compassionate healthcare providers.

This article was reviewed by Twentyeight Health's medical team.

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