The most common sexually transmitted infections in the United States are chlamydia, gonorrhea, syphilis, HPV, herpes, HIV, and trichomoniasis. In 2024 alone, over 1.5 million chlamydia cases and more than 540,000 gonorrhea cases were reported to the CDC. Many of these infections cause no symptoms at all, which is why they spread so easily and why routine screening matters.
Chlamydia
Chlamydia is the most frequently reported bacterial STI in the country, with roughly 1.5 million cases reported in 2024. It’s also one of the sneakiest: 70 to 80% of women and up to 50% of men with chlamydia have no symptoms whatsoever. When symptoms do appear, they typically include painful urination, unusual discharge from the penis or vagina, and pain during sex.
Left untreated, chlamydia can cause serious problems. About 10 to 15% of women with untreated chlamydia develop pelvic inflammatory disease (PID), an infection of the uterus and fallopian tubes that can lead to chronic pain and infertility. Chlamydia can also silently damage the fallopian tubes without ever causing noticeable symptoms, making permanent reproductive harm possible even in people who feel perfectly fine. The infection is curable with a short course of antibiotics, typically taken over seven days.
Gonorrhea
Gonorrhea was responsible for more than 543,000 reported cases in 2024. Symptoms overlap with chlamydia: burning during urination, discharge, and in women, bleeding between periods. Up to 50% of women and about 10% of men with gonorrhea show no symptoms. Like chlamydia, untreated gonorrhea is a major cause of PID and infertility.
What makes gonorrhea increasingly concerning is antibiotic resistance. The bacteria that cause it have gradually developed resistance to many of the drugs once used to treat it, narrowing the options. Current first-line treatment is a single injection of a powerful antibiotic. If you’re diagnosed, your provider will likely want a follow-up test to confirm the infection cleared.
Syphilis
Syphilis is less common than chlamydia or gonorrhea, with about 190,000 total cases reported in 2024, but it progresses through distinct stages that become increasingly dangerous over time.
In the primary stage, a firm, round, painless sore appears at the site where the bacteria entered your body. This sore lasts three to six weeks and heals on its own, which tricks many people into thinking the problem resolved. It hasn’t. In the secondary stage, a rash develops, often on the palms of your hands or soles of your feet. It can be rough or reddish-brown, and it usually doesn’t itch. You might also experience fever, swollen glands, sore throat, patchy hair loss, and fatigue.
After the secondary stage, syphilis enters a latent period where there are no visible signs at all. This can last years. If still untreated 10 to 30 years after the original infection, tertiary syphilis can damage the heart, blood vessels, brain, and nervous system, and it can be fatal. Syphilis is treatable with penicillin at any stage, but the damage done in later stages can be permanent. Congenital syphilis, passed from mother to baby during pregnancy, is also rising sharply, with nearly 4,000 cases reported in 2024.
HPV (Human Papillomavirus)
HPV is the single most common sexually transmitted infection. It spreads through intimate skin-to-skin contact during vaginal, anal, or oral sex, and a person can carry it for years without knowing. There are many strains. Low-risk strains cause genital, anal, or oral warts. High-risk strains can lead to cervical, anal, penile, vaginal, vulvar, and throat cancers.
The HPV vaccine is the most effective prevention tool available. It’s recommended as a routine vaccination at age 11 or 12, can be given as early as age 9, and catch-up vaccination is recommended for everyone through age 26. Adults between 27 and 45 who weren’t vaccinated earlier can still receive it after discussing it with a healthcare provider. Condoms offer little protection against HPV because the virus transmits through skin contact in areas a condom doesn’t cover.
Herpes (HSV)
Genital herpes is caused by herpes simplex virus, most often type 2 (HSV-2), though type 1 (the strain that typically causes cold sores) can also infect the genitals through oral sex. The hallmark symptom is painful blisters or sores around the genitals or rectum that break open, scab over, and heal. Many people with herpes experience mild or no symptoms and don’t realize they carry the virus.
There is no cure for herpes. Outbreaks tend to become less frequent and less severe over time, and antiviral medications can shorten outbreaks and reduce transmission to partners. Condoms reduce herpes transmission by roughly 40%, a lower figure than for many other STIs, because herpes can spread from skin not covered by a condom.
HIV
HIV attacks the immune system’s infection-fighting cells, gradually weakening the body’s ability to defend itself against disease. Without treatment, HIV progresses to AIDS. With modern treatment, people with HIV can live long, healthy lives and reduce the amount of virus in their body to undetectable levels, which also prevents sexual transmission.
HIV spreads through sexual contact, shared needles, and from mother to child during pregnancy or breastfeeding. Condoms, when used correctly and consistently, reduce HIV transmission by about 85%. Pre-exposure prophylaxis (PrEP), a daily pill or injectable medication, offers additional protection for people at higher risk. The CDC recommends that everyone between ages 13 and 64 be tested for HIV at least once, with more frequent testing for those at increased risk.
Trichomoniasis
Trichomoniasis is caused by a parasite rather than a bacterium or virus, making it unique among common STIs. Between 70 and 85% of people with the infection have minimal or no symptoms, and untreated infections can persist for months to years. When symptoms do occur, women may notice a yellow-green, foul-smelling vaginal discharge and vulvar irritation. Men sometimes experience symptoms related to urethral or prostate inflammation.
Trichomoniasis is curable with oral medication. Traditional diagnostic methods like wet-mount microscopy miss a significant number of cases, detecting only 44 to 68% of infections. Newer molecular tests are far more accurate, with sensitivity above 96%, so it’s worth asking for one of these if trichomoniasis is a concern.
Why Many STIs Go Undetected
The thread running through nearly all of these infections is how often they produce no symptoms. Chlamydia, gonorrhea, trichomoniasis, HPV, herpes, and even early HIV can all be present without any obvious signs. This means you can’t rely on how you feel to know your status. Screening is the only reliable way to catch these infections early, before they cause complications or get passed to someone else.
Current guidelines recommend annual chlamydia and gonorrhea screening for all sexually active women under 25. Women 25 and older should be screened if they have risk factors like new or multiple partners. Men who have sex with men should be screened at least annually, and every three to six months if at higher risk. HIV screening is recommended at least once for all adults aged 13 to 64.
How Well Condoms Protect Against Each STI
Condoms are highly effective against some STIs and less so against others, depending on how the infection spreads. For HIV and hepatitis B, which transmit through bodily fluids, consistent and correct condom use reduces transmission by roughly 85 to 90%. For gonorrhea, studies show a 49 to 75% risk reduction. For chlamydia, one study found about a 33% reduction with consistent use, and for syphilis, consistent correct use reduces transmission by 50 to 71%.
Condoms are less effective against infections that spread through skin-to-skin contact. Herpes transmission drops by only about 40% with condom use, and condoms provide no significant reduction in HPV transmission. This doesn’t mean condoms aren’t worth using. They remain one of the most important tools for reducing STI risk overall. But for HPV specifically, vaccination is the far more effective strategy.