A venereal disease is an infection spread through sexual contact. The term comes from Venus, the Roman goddess of love, and was the standard medical label for decades. Today, health agencies including the CDC use “sexually transmitted infection” (STI) instead, because most of these infections can be detected and treated before they ever cause noticeable disease. The shift in language reflects a shift in priorities: catching infections early, before they do damage. Regardless of which term you encounter, they all describe the same group of conditions.
Why the Name Changed
There’s a meaningful distinction behind the newer terminology. An STI is the initial infection itself: a virus, bacterium, fungus, or parasite that enters the body through sexual contact. An STD (sexually transmitted disease) is what can develop when that infection progresses far enough to cause symptoms or organ damage. “Venereal disease” made no such distinction. Because the whole point of modern screening is to find and treat infections before they become diseases, the CDC and most medical organizations now default to “STI.” You’ll still see “STD” in older data sets and some public health reports, but all three terms refer to the same core group of infections.
The Most Common Types
STIs fall into a few categories based on what causes them.
Bacterial infections include chlamydia, gonorrhea, and syphilis. These are curable with antibiotics when caught early. Chlamydia is by far the most commonly reported, with roughly 1.5 million cases documented in the U.S. in 2024 alone. Gonorrhea accounted for about 543,000 cases, and syphilis (all stages combined) added another 190,000.
Viral infections include HIV, genital herpes, hepatitis B and C, and human papillomavirus (HPV). Viral STIs generally can’t be cured, but they can be managed with medication or, in the case of HPV and hepatitis B, prevented with vaccines. HPV is so common that most sexually active people will encounter it at some point in their lives.
Parasitic infections like trichomoniasis are caused by a tiny organism rather than a bacterium or virus. Trichomoniasis is curable with prescription medication.
How These Infections Spread
Some STIs travel through body fluids like semen, vaginal secretions, or blood. HIV, gonorrhea, chlamydia, and hepatitis B spread this way. Others, including herpes, HPV, and syphilis, spread through direct skin-to-skin contact with an infected area, which means they can be transmitted even when a condom covers the most common sites of exposure but not all of them.
Oral, vaginal, and anal sex can all transmit STIs. A few can also pass from a pregnant person to their baby during pregnancy or delivery. Congenital syphilis, for example, affected nearly 4,000 newborns in the U.S. in 2024.
Many Infections Have No Symptoms
One of the most important things to understand about STIs is that the majority of cases produce no obvious symptoms, at least initially. Research estimates that roughly 61% of chlamydia infections, 53% of gonorrhea infections, and 57% of trichomoniasis infections in women are completely asymptomatic. People with these infections feel fine, look fine, and have no reason to suspect anything is wrong without a test.
This is exactly why the old term “venereal disease” was misleading. It implied that you’d know something was wrong. In reality, the infections most likely to cause long-term damage are often the ones you never feel.
What Happens If an STI Goes Untreated
Left alone, bacterial STIs can cause serious complications. About 10 to 15 percent of women with untreated chlamydia develop pelvic inflammatory disease (PID), an infection of the uterus, fallopian tubes, and surrounding tissue. Chlamydia can also silently damage the fallopian tubes without ever triggering symptoms. The resulting scarring can lead to infertility or life-threatening ectopic pregnancies.
Untreated syphilis progresses through stages over months and years, eventually affecting the heart, brain, and nervous system. Untreated gonorrhea can spread to the bloodstream and joints. And untreated viral infections carry their own risks: certain strains of HPV cause cervical and other cancers, while unmanaged HIV progressively destroys the immune system.
How Testing Works
Testing is straightforward and varies by infection. Chlamydia and gonorrhea are typically detected through a urine sample or a swab of the genital area (and sometimes the throat or rectum, depending on sexual history). HIV and syphilis require a blood test, though HIV can also be screened with an oral swab. Herpes testing uses a combination of physical examination, swabs of active sores, and blood tests that reveal past exposure. HPV is detected through Pap smears and related cervical tests. Trichomoniasis can be identified by urine, swab, or physical exam.
One important caveat: infections don’t show up on tests immediately after exposure. Each has a window period, so if you test too early after a potential exposure, you may need to retest a few weeks or months later to get an accurate result.
Who Should Get Screened
National screening recommendations are more aggressive than many people realize. All sexually active women aged 24 and younger are recommended to be screened annually for chlamydia and gonorrhea. Women 25 and older should be screened if they have risk factors like new or multiple partners. All adolescents and adults aged 15 to 65 are recommended to be screened for HIV at least once, with more frequent screening for those at higher risk. Syphilis screening is recommended for anyone at increased risk and universally for all pregnant people, ideally early in pregnancy. Hepatitis C screening is recommended for all adults aged 18 to 79.
Prevention
Consistent condom use significantly reduces transmission for most STIs. In studies of couples where one partner had HIV, consistent condom use lowered the uninfected partner’s risk by 71 to 80 percent in heterosexual relationships and by 70 to 91 percent in male same-sex relationships. Condoms also reduce the risk of chlamydia, gonorrhea, hepatitis B, trichomoniasis, and, when the infected area is covered, HPV, herpes, and syphilis.
Vaccination is even more effective for the infections it covers. The HPV vaccine and hepatitis B vaccine are among the most reliable ways to prevent those specific infections. HPV vaccination is routinely given starting around age 11 or 12 but can be given through age 26, and in some cases up to 45. Hepatitis B vaccination is part of the standard childhood schedule and is also recommended for unvaccinated adults at risk.
Reducing your number of partners, having open conversations about testing, and getting screened at recommended intervals all lower your cumulative risk. The combined total of reported chlamydia, gonorrhea, and syphilis cases in the U.S. dropped 9 percent from 2023 to 2024, marking a third consecutive year of decline, but more than 2.2 million cases were still reported. These are common infections, and routine screening remains the most practical way to catch them before they cause harm.