Sexually transmitted diseases fall into three main categories based on what causes them: bacteria, viruses, and parasites. This matters because bacterial and parasitic STDs can be cured with medication, while viral STDs are treatable but stay in your body long-term. In 2024, more than 2.2 million cases of just chlamydia, gonorrhea, and syphilis were reported in the United States, and most STDs cause no obvious symptoms, which means many more cases go undetected.
Bacterial STDs
Bacterial STDs are caused by bacteria that pass between partners during sexual contact. The key thing to know: all of them are curable with antibiotics when caught early. The three most common are chlamydia, gonorrhea, and syphilis.
Chlamydia
Chlamydia is the most frequently reported STD in the U.S., with roughly 1.5 million cases in 2024. It usually causes no symptoms at all, which is why routine screening matters so much. When symptoms do appear, they show up a few days to several weeks after infection and often get mistaken for a urinary tract infection. You might notice unusual discharge, painful urination, bleeding between periods, or rectal pain. A single course of antibiotics clears it up, but untreated chlamydia can lead to pelvic inflammatory disease and fertility problems.
Gonorrhea
Gonorrhea accounted for over 543,000 reported cases in 2024. Like chlamydia, it frequently produces no symptoms, especially in women. When symptoms do develop, they typically include burning during urination and unusual discharge. Gonorrhea is curable with antibiotics, though antibiotic-resistant strains have become a growing concern, which is why follow-up testing is important. Untreated gonorrhea can also cause pelvic inflammatory disease and can spread to the blood or joints.
Syphilis
Syphilis is less common than chlamydia or gonorrhea, with about 190,000 total cases reported in 2024, but it’s more dangerous if left untreated because it progresses through distinct stages over years.
In the primary stage, a firm, round, painless sore appears where the bacteria entered your body, typically on the genitals, anus, rectum, or mouth. Because it doesn’t hurt, many people never notice it. The sore heals on its own within three to six weeks, but the infection isn’t gone.
The secondary stage brings skin rashes, often on the palms of your hands or soles of your feet, along with fever, swollen lymph nodes, sore throat, patchy hair loss, and fatigue. After this, syphilis enters a latent stage with no visible signs, sometimes lasting years. If still untreated 10 to 30 years later, tertiary syphilis can damage the heart, blood vessels, brain, and nervous system, potentially causing death. At any stage, syphilis can also spread to the eyes (causing vision changes or blindness), ears (causing hearing loss or vertigo), or brain (causing confusion, memory problems, and personality changes). Syphilis is fully curable with antibiotics, especially when treated early.
Viral STDs
Viral STDs are treatable but not curable. The virus remains in your body after infection, though medication can control symptoms and reduce transmission. Two of the most common viral STDs now have vaccines available.
Human Papillomavirus (HPV)
HPV is the most common STD overall. There are many strains: some cause genital warts (flat or raised growths on the genitals), while others cause no visible symptoms but can lead to cervical, anal, or throat cancers over time. Most HPV infections actually clear on their own without treatment. When genital warts are present, they can be treated, but the treatment targets the warts themselves rather than eliminating the virus.
The HPV vaccine is recommended for everyone starting at age 11 or 12, though it can be given as early as 9 and is recommended through age 26 for anyone not previously vaccinated. Adults aged 27 to 45 may still benefit and can discuss vaccination with a provider.
Genital Herpes (HSV)
Genital herpes is caused by herpes simplex virus type 1 or type 2. The classic sign is painful, blister-like sores on the genitals, anus, or mouth, but many infected people never develop noticeable sores or have outbreaks so mild they go unrecognized. Herpes is a lifelong infection with recurring outbreaks, though outbreaks typically become less frequent over time. Daily antiviral medication can reduce the severity and frequency of outbreaks and lower the risk of passing the virus to partners, but it doesn’t eliminate the virus from your body.
HIV
HIV attacks the immune system. Shortly after infection, many people experience flu-like symptoms: fever, fatigue, swollen lymph nodes, sore throat, rash, or joint pain. Some people notice nothing at all. Without treatment, HIV gradually destroys immune cells over years, eventually leading to AIDS. With modern antiretroviral treatment, people with HIV can live long, healthy lives and reduce the virus to undetectable levels, which also prevents transmission to sexual partners.
Hepatitis B
Hepatitis B attacks the liver and spreads through sexual contact, blood, and from mother to child during birth. Some people clear the infection on their own, while others develop chronic hepatitis B, which can lead to liver damage, cirrhosis, or liver cancer over decades. A highly effective vaccine is available and recommended for all unvaccinated, sexually active people.
Parasitic STDs
Parasitic STDs are caused by tiny organisms that live on or inside the body. They’re all curable with medication.
Trichomoniasis
Trichomoniasis is the most common curable STD. It’s caused by a parasite that typically infects the lower genital tract in women (vulva, vagina, cervix, or urethra) and the urethra in men. It usually spreads from penis to vagina or vagina to penis, and can also spread between vaginas. Many people with trichomoniasis have no symptoms, making it impossible to diagnose based on how you feel alone. When symptoms appear, they can include itching, burning, unusual discharge, or discomfort during urination. A single course of oral medication cures the infection, but your partner needs treatment at the same time to prevent reinfection. You should get retested about three months after treatment.
Pubic Lice and Scabies
Pubic lice (sometimes called “crabs”) are tiny insects that attach to coarse body hair, especially in the genital area. Scabies is caused by microscopic mites that burrow into the skin. Both cause intense itching and are spread through close physical contact. Over-the-counter or prescription topical treatments kill the lice or mites, though you’ll also need to wash bedding and clothing to prevent reinfestation.
Why Most STDs Go Unnoticed
The majority of STDs are asymptomatic. Globally, more than 1 million curable STIs are acquired every day, and most of those infections produce no symptoms. Chlamydia, gonorrhea, HPV, herpes, trichomoniasis, and even HIV can all be present without any obvious signs. This is why screening based on symptoms alone misses most infections. Regular testing is the only reliable way to know your status, particularly if you have new or multiple partners.
Testing Window Periods
Getting tested too soon after exposure can produce a false negative. Each STD has a window period, the minimum time needed after exposure for the infection to show up on a test.
- Chlamydia and gonorrhea: One week catches most cases; two weeks catches nearly all.
- Trichomoniasis: One week catches most; one month catches nearly all.
- Syphilis: One month catches most; three months catches nearly all.
- HIV (blood test): Two weeks catches most; six weeks catches nearly all. Oral swab tests take longer, with one month catching most and three months catching nearly all.
- Herpes (blood test): One month catches most; four months catches nearly all.
- Hepatitis B: Three to six weeks.
- Hepatitis C: Two months catches most; six months catches nearly all.
- HPV: No routine screening test for genital or anal warts. Cervical HPV is detected through Pap smears, typically three weeks to a few months after infection.
If you’ve had a recent exposure, testing at the earliest window and then retesting at the longer interval gives you the most reliable results.