The most common sexually transmitted infections range from extremely widespread viruses that most sexually active people encounter at some point to bacterial infections that are fully curable with antibiotics. In the United States alone, more than 2.2 million cases of just three reportable STIs (chlamydia, gonorrhea, and syphilis) were documented in 2024. When you factor in infections that aren’t routinely reported, like HPV, herpes, and trichomoniasis, the total number of STIs acquired each year is far higher. Here are the 10 most significant sexually transmitted infections, ranked roughly by how common they are.
1. Human Papillomavirus (HPV)
HPV is the single most common sexually transmitted infection in the world. Nearly all sexually active people will contract at least one strain at some point in their lives. Most of the time, the immune system clears the virus within a year or two without any symptoms or lasting effects. The trouble comes from a handful of high-risk strains that persist and can cause cancer. These strains are responsible for virtually all cervical cancers, most anal cancers, and a share of throat, vaginal, vulvar, and penile cancers.
The HPV vaccine is highly effective against the strains most likely to cause cancer and genital warts. It’s recommended for preteens but can be given through age 26, and in some cases up to 45. Routine cervical screening (Pap tests or HPV tests) catches precancerous changes early, which is why cervical cancer rates have dropped significantly in countries with strong screening programs.
2. Genital Herpes (HSV-1 and HSV-2)
Genital herpes is caused by two related viruses. HSV-2 is the traditional cause, infecting an estimated 520 million people aged 15 to 49 worldwide, roughly 13% of that age group. But HSV-1, long associated with cold sores on the mouth, now accounts for a growing share of genital infections. Globally, about 376 million people in the same age range have genital HSV-1, meaning nearly 900 million people worldwide are living with some form of genital herpes.
Many people with herpes never develop noticeable sores, or they mistake mild symptoms for something else. When outbreaks do occur, they typically involve painful blisters or ulcers around the genitals or rectum that heal within a few weeks. The first outbreak tends to be the worst, and recurrences usually become less frequent over time. Herpes can’t be cured, but daily antiviral medication reduces outbreaks and lowers the chance of passing the virus to a partner.
3. Chlamydia
Chlamydia is the most frequently reported bacterial STI in the United States, with over 1.5 million cases documented in 2024 at a rate of about 446 per 100,000 people. The real number is higher because most infections produce no symptoms at all, especially in women. When symptoms do appear, they typically include painful urination and unusual discharge.
Left untreated, chlamydia can silently damage the reproductive system. In women, it can spread to the uterus and fallopian tubes, causing pelvic inflammatory disease, chronic pain, and infertility. In men, it can lead to infection of the tube that carries sperm, though this is less common. The good news: a simple urine test or swab detects it, and a short course of antibiotics clears it completely. Annual screening is recommended for sexually active women under 25.
4. Gonorrhea
Gonorrhea is the second most reported STI in the U.S., with 543,409 cases in 2024. Like chlamydia, it often flies under the radar. Most women with gonorrhea have no symptoms, and rectal infections in both sexes are frequently silent. When symptoms do show up, men typically notice a burning sensation while urinating and a yellow or green discharge from the penis. Women may experience increased vaginal discharge, painful urination, or bleeding between periods.
Untreated gonorrhea carries the same risks as chlamydia for reproductive health, and it can also spread to the bloodstream and joints. A growing concern is antibiotic resistance. Several first-line treatments have become less effective over the years, narrowing the options for reliable treatment. Current guidelines call for a specific injectable antibiotic, but resistance surveillance remains critical.
5. Trichomoniasis
Trichomoniasis, often called “trich,” is caused by a tiny parasite rather than a bacterium or virus. It’s one of the most common STIs worldwide, yet it gets relatively little attention because about 70% of infected people have no symptoms whatsoever. When symptoms do occur, women may notice itching, burning, or a frothy, foul-smelling discharge. Men occasionally experience irritation inside the penis or mild discharge after urination.
Trich matters more than its mild reputation suggests. It causes genital inflammation that makes it easier to acquire or transmit HIV. Pregnant women with trich face a higher risk of preterm delivery and having a baby with low birth weight. A single dose of oral antibiotic cures the infection, but both partners need treatment at the same time to avoid passing it back and forth.
6. Syphilis
Syphilis has been surging. In 2024, the U.S. reported 190,242 total syphilis cases, with 41,496 in the most infectious primary and secondary stages. The crisis is especially stark in newborns: congenital syphilis cases have risen nearly 700% since 2015, when just 495 cases were reported. In 2024, 3,941 babies were born with the infection.
Syphilis progresses through distinct stages if untreated. The first sign is a painless sore (called a chancre) at the site of infection, which heals on its own within a few weeks. Months later, a secondary stage can bring rashes, fever, and swollen lymph nodes. After that, the infection goes quiet for years before potentially advancing to a late stage that damages the brain, heart, and other organs. Early syphilis is easily cured with a penicillin injection. Testing requires a blood draw, and the detection window is two to six weeks after exposure, so testing too soon can produce a false negative.
7. HIV
An estimated 1.3 million people worldwide acquired HIV in 2024. While that number has dropped dramatically from its peak, HIV remains one of the most serious STIs because, without treatment, it destroys the immune system and leads to AIDS. Modern antiretroviral therapy, however, has transformed the prognosis. People diagnosed early who take daily medication can expect a near-normal lifespan and reach a viral load so low that they effectively cannot transmit the virus to sexual partners.
Prevention has also advanced. Pre-exposure prophylaxis (PrEP), a daily pill or a long-acting injection given every two months, reduces the risk of acquiring HIV through sex by more than 99% when used consistently. The testing window for HIV is three to four weeks after exposure, so an initial negative result after a recent encounter should be followed up with a second test once that window has passed.
8. Hepatitis B
Hepatitis B is a viral liver infection spread through blood and body fluids, including semen and vaginal secretions. Among reported cases with known risk information, roughly 23% involved having multiple sex partners, making sexual contact one of the leading routes of transmission. Most adults who contract hepatitis B clear the virus on their own within a few months, but about 5% develop a chronic infection that can lead to liver scarring, liver failure, or liver cancer over decades.
A highly effective vaccine has been available since the 1980s and is now part of the routine childhood immunization schedule. Despite this, adult vaccination coverage remains low. As of 2018, only about 30% of adults 19 and older had completed the full vaccine series. Universal vaccination is now recommended for all adults through age 59, and for older adults with risk factors.
9. Mycoplasma Genitalium
Mycoplasma genitalium is a lesser-known bacterial STI that has gained attention in recent years as testing has become more widely available. It causes 15% to 20% of non-gonococcal urethritis cases in men and can be found in 10% to 30% of women with cervical inflammation. In women, it’s also linked to pelvic inflammatory disease. Many infections are asymptomatic, which allows the bacteria to spread undetected.
The biggest challenge with this infection is antibiotic resistance. Resistance to the most commonly used antibiotic class has risen sharply, with markers of resistance found in 44% to 90% of tested samples across the U.S., Canada, Western Europe, and Australia. This means treatment often requires resistance-guided testing, where the lab checks which antibiotics the specific strain is still susceptible to before prescribing. Without this approach, failed treatments can actually make the bacteria more resistant.
10. Hepatitis C
Hepatitis C is primarily transmitted through blood-to-blood contact, most commonly via shared needles. Sexual transmission is less efficient but does occur, particularly among men who have sex with men and during sexual activities that involve blood exposure. It’s included among STIs because sexual contact is a recognized transmission route, even if it’s not the dominant one.
Chronic hepatitis C was once a lifelong condition with limited treatment options. That changed dramatically with the development of direct-acting antiviral medications, which now cure more than 95% of infections in about 8 to 12 weeks of oral treatment. Many people with hepatitis C have no symptoms for years or even decades, so screening is important. The CDC recommends that all adults be tested at least once in their lifetime.
How Testing Timelines Work
One practical detail that trips people up is timing. Every STI has a “window period,” the gap between exposure and when a test can reliably detect the infection. For chlamydia and gonorrhea, a test taken too soon after exposure (under two weeks) may miss a new infection. For syphilis, the window is two to six weeks. For HIV, it’s three to four weeks. If you’re tested within days of a potential exposure and everything comes back negative, those results may not be accurate. A follow-up test after the window period gives you a more reliable answer.
Routine screening, even without symptoms, is the single most effective way to catch infections early. Most of the STIs on this list are either curable or highly manageable with treatment, but only if they’re actually detected. The fact that so many of these infections are frequently asymptomatic makes regular testing essential for anyone who is sexually active.