The 20 types of STDs are chlamydia, gonorrhea, syphilis, trichomoniasis, genital herpes, human papillomavirus, HIV, hepatitis B, hepatitis C, mpox, chancroid, lymphogranuloma venereum, granuloma inguinale, Mycoplasma genitalium, pubic lice, scabies, molluscum contagiosum, hepatitis A, cytomegalovirus, and bacterial vaginosis. Most are bacterial, viral, or parasitic; a few are sexually associated syndromes rather than single pathogens. The first answer is that risk depends more on exposure site, skin or mucosal contact, and testing window than on the label alone. A negative test soon after exposure can be falsely reassuring if it is done before the pathogen becomes detectable.
Transmission Mechanisms That Change the Numbers
STD transmission is not one event called sex. It is a set of exposures at mucosal sites: cervix, urethra, rectum, pharynx, and skin. The pathogen must reach susceptible cells, survive local defenses, and establish infection. That is why the same organism can be easy to transmit by anal sex and harder by oral sex.
HIV shows how much act and site matter. CDC per-act estimates without prevention are about 0.04% for insertive vaginal sex, 0.08% for receptive vaginal sex, 0.11% for insertive anal sex, and 1.38% for receptive anal sex. These are averages, and viral load, genital ulcers, and bleeding raise them. A single number cannot describe every encounter.
HPV and herpes change the usual calculus because they spread by skin-to-skin contact. Condoms reduce risk, but they do not cover every infected square centimeter. HPV is the most common sexually transmitted infection; about 80% of sexually active people acquire it by age 45, per CDC estimates. Most clear within 12 to 24 months, while persistent high-risk types drive cervical and other cancers.
HSV-2 prevalence is lower than HPV but still common. About 12% of US people aged 14 to 49 have HSV-2, and most do not know it. In plain terms: the most transmissible STD is often the one with no visible symptoms and no routine test.
The 20 Types of STDs by Pathogen and Test
The table below maps the 20 types of STDs to their cause, core mechanism, common clue, and best first test. It is a comparison of biology and diagnosis, not a ranking of severity. Some entries are rare in high-income countries but remain important because travel and sexual networks move pathogens.
| Type | Cause and class | Core mechanism | Common clue | Best initial test |
|---|---|---|---|---|
| Chlamydia | Chlamydia trachomatis bacterium | Infects columnar epithelium of cervix, urethra, rectum, and pharynx | Discharge, dysuria, pelvic pain, or none | NAAT of urine or swab |
| Gonorrhea | Neisseria gonorrhoeae bacterium | Pili-mediated mucosal attachment; can disseminate | Purulent discharge, dysuria, pelvic pain | NAAT; culture if resistance suspected |
| Syphilis | Treponema pallidum spirochete | Penetrates mucosa or skin, then disseminates in stages | Painless chancre, rash, latent infection | Darkfield or PCR of lesion; serology |
| Trichomoniasis | Trichomonas vaginalis protozoan | Colonizes vagina and urethra; alters local flora | Frothy discharge, itch, dysuria | NAAT; wet mount is less sensitive |
| Genital herpes | HSV-1 or HSV-2 virus | Latency in sensory ganglia with reactivation | Painful vesicles or ulcers | PCR from lesion; type-specific serology |
| HPV | Human papillomavirus | Mucosal infection; E6 and E7 proteins disrupt cell cycle | Warts or none; cancer precursors | Cervical HPV or Pap test; warts are clinical |
| HIV | Human immunodeficiency virus | Infects CD4 T cells, integrates, and causes immune decline | Flu-like seroconversion, later infections | HIV antigen/antibody; RNA if early |
| Hepatitis B | Hepatitis B virus | Blood and sexual exposure; liver infection | Jaundice, fatigue, or none | HBsAg, anti-HBc, HBV DNA |
| Hepatitis C | Hepatitis C virus | Bloodborne; sexual transmission is less efficient | Often silent; liver inflammation | HCV RNA; antibody |
| Mpox | Monkeypox virus | Skin or mucosal contact with lesions and fluids | Rash, vesicles, fever, lymph nodes | PCR of lesion |
| Chancroid | Haemophilus ducreyi bacterium | Breaks skin and produces a painful ulcer | Painful ragged ulcer and tender nodes | PCR or culture where available |
| Lymphogranuloma venereum | C. trachomatis serovars L1 to L3 | Invasive chlamydia affecting lymph nodes and rectum | Painless ulcer, buboes, proctitis | NAAT plus genotyping |
| Granuloma inguinale | Klebsiella granulomatis bacterium | Chronic genital ulcer disease | Painless beefy ulcer | Biopsy or PCR; rare |
| Mycoplasma genitalium | M. genitalium bacterium | Urethral and cervical inflammation; resistance is common | Urethritis, cervicitis, pelvic pain | NAAT; resistance testing when available |
| Pubic lice | Pthirus pubis parasite | Claws grasp hair; spreads by skin contact | Itch, visible lice or nits | Visual inspection |
| Scabies | Sarcoptes scabiei mite | Burrows in skin; sensitization causes itch | Intense itch, burrows, rash | Visual inspection or dermoscopy |
| Molluscum contagiosum | Poxvirus | Skin contact; epidermal nodules | Dome-shaped papules with a dimple | Clinical diagnosis; PCR is rare |
| Hepatitis A | Hepatitis A virus | Fecal-oral spread; sexual contact among men who have sex with men | Jaundice, nausea, or none | IgM anti-HAV; RNA |
| Cytomegalovirus | Cytomegalovirus | Saliva, urine, and sexual fluids; latency | Usually silent; mono-like illness | IgM or PCR; not a routine STI panel |
| Bacterial vaginosis | Polymicrobial dysbiosis | Not a single pathogen; sexually associated | Thin discharge and odor | Amsel criteria or Nugent score |
Bacterial vaginosis is not a classic STD in the same sense as gonorrhea or syphilis. It is a sexually associated change in vaginal flora, included here because many sexual health visits code it with STI care. That distinction matters: treating BV does not protect against chlamydia, HIV, or HPV.
Symptom Patterns and Red Flags
Symptoms follow anatomy more than pathogen name. Cervicitis can cause discharge or bleeding after sex, while urethritis more often causes dysuria. Rectal infection may cause pain, mucus, or bleeding, but it can also be silent. Pharyngeal gonorrhea and chlamydia usually produce no throat symptoms at all.
Silent infection is the rule, not the exception, for several common STDs. Roughly half of men and up to 70% of women with chlamydia have no symptoms. Gonorrhea can be silent at the throat and rectum. Syphilis hides in latent stages after a painless ulcer heals. HSV-2 shedding occurs on many days without lesions, which is why “no outbreak” is not the same as “no transmission risk.”
Get same-day medical advice for any of these warning signs:
- Fever with a new rash, especially on the palms or soles, or with mouth ulcers
- Pelvic pain, fever, abnormal discharge, or pain during sex
- Painful testicular swelling, rectal pain, or rectal discharge
- A new genital ulcer, blister, or wart that persists beyond 2 weeks
- Jaundice, dark urine, or right upper abdominal pain
- Pregnancy with a known exposure or a positive STD test
These signs do not diagnose a specific infection. They do mean that a delayed home test or watchful waiting is the wrong move.
Testing Windows and False Reassurance
Testing windows differ because each test detects a different biological signal. A PCR test finds DNA or RNA within days. An antibody test waits for the immune response, which can take weeks. A negative result before the window closes is a preliminary result, not a clean bill of health.
The table uses typical windows from exposure to reliable detection. The exact window depends on the test brand, specimen site, immune status, and whether treatment or vaccination has occurred. When a number is safety-critical, the table follows CDC’s 2021 STI treatment guidance where available.
| Infection and test | Earliest typical detection | Reliable window with standard test | Main caveat |
|---|---|---|---|
| HIV RNA | 10 to 14 days | 10 to 14 days | Not available in every clinic |
| HIV antigen/antibody | 18 to 45 days | 45 days for most tests | Rapid antibody tests can lag to 90 days |
| Syphilis serology | 4 to 6 weeks | 6 weeks; repeat at 3 months after early exposure | Early primary syphilis can be seronegative |
| Chlamydia and gonorrhea NAAT | 1 to 2 weeks | 2 weeks | Site-specific swabs matter for throat and rectum |
| Trichomoniasis NAAT | 1 to 2 weeks | 2 weeks | Wet mount misses a large share of infections |
| HSV PCR from lesion | 1 to 2 days from lesion onset | Test the active lesion immediately | Blood serology takes 12 to 16 weeks to turn positive |
| Hepatitis B | HBsAg at 4 to 6 weeks | 6 weeks to 6 months for full interpretation | Vaccination changes serology |
| Hepatitis C | HCV RNA at 1 to 2 weeks | RNA at 2 weeks; antibody at 12 weeks | Sexual transmission is less efficient than blood exposure |
These windows are not screening intervals. The 90-day HIV antibody window, the annual CDC screening recommendation for sexually active gay and bisexual men, and the 5-year cervical HPV screening interval answer different questions. One asks whether a recent exposure was detected; another asks how often to look for silent infection.
In plain terms: a negative test at 3 days after exposure cannot rule out HIV, syphilis, or hepatitis B. It can only tell you what was detectable at that moment. The repeat test date is part of the result, not an optional extra.
Misconceptions That Survive a Negative Panel
A “full STD panel” is not a universal standard. Many clinics test HIV, syphilis, chlamydia, and gonorrhea, then stop. That panel misses trichomoniasis, Mycoplasma genitalium, HSV, hepatitis A, hepatitis B, hepatitis C, HPV, and rare ulcer diseases unless specific risk factors trigger those tests. No single blood draw covers all 20 types of STDs.
A negative herpes blood test is easy to misread. Type-specific HSV-2 serology takes 12 to 16 weeks to become positive after infection. A negative result at 2 weeks does not exclude new HSV. Also, a positive HSV-1 blood test cannot prove that the infection is genital, because HSV-1 is common orally.
HPV testing is not a general STD test. There is no approved routine HPV test for men, and genital warts are diagnosed by inspection. Cervical HPV testing is a cancer-screening tool for people with a cervix, not a proof of who infected whom. That is why HPV vaccination and cervical screening matter more than partner testing.
Antibiotic resistance changes the old assumptions. Mycoplasma genitalium resistance to macrolides is common enough that guidelines recommend resistance testing when available. Gonorrhea has documented resistance to multiple drug classes, so culture and susceptibility testing matter in treatment failure. A diagnosis is not a prescription; the drug and the follow-up test both count.
What to Actually Do After Exposure or Diagnosis
If an exposure is recent, call a sexual health clinic the same day. HIV post-exposure prophylaxis works best when started within 2 hours and must begin within 72 hours. Do not wait for symptoms, and do not use a home test to decide whether to seek PEP. The exposure history, not the test result, drives that decision.
Use barriers for oral, vaginal, and anal sex while awaiting tests. Condoms and dental dams reduce risk but do not eliminate skin-contact infections such as HPV, HSV, and syphilis. Vaccination is concrete protection: HPV vaccine, hepatitis A and B vaccines, and mpox vaccine when eligible. These vaccines prevent specific infections; they do not replace testing.
If a test is positive, complete the full treatment course and ask which follow-up test is needed. For chlamydia or gonorrhea, avoid sex until 7 days after treatment completion or a single-dose regimen. For syphilis, follow the staged treatment plan and repeat serology at 3, 6, 9, and 12 months when advised. For HIV, start antiretroviral therapy as soon as possible; modern treatment can suppress viral load to undetectable levels.
Tell partners without guessing who infected whom. Partner notification is a public health action, not a blame exercise. Many clinics offer anonymous notification tools. If a partner cannot be reached, the clinic can still arrange testing and treatment for people at risk.
Limitations of a Negative STD Panel
A negative panel is a snapshot of detectable infections at one time. It cannot prove the absence of HPV, HSV, or early HIV. It cannot tell whether a throat infection was missed because only urine was tested. It cannot replace a physical exam when an ulcer, wart, or discharge is visible.
Site matters more than many people realize. A urine test is good for urethral chlamydia and gonorrhea, but it misses rectal or pharyngeal infection. A blood test for syphilis may be negative in early primary disease. A lesion swab for HSV is most useful within 1 to 2 days of blister formation. The specimen must match the exposure.
Screening intervals are not exposure tests. Per the 2018 USPSTF recommendation, average-risk cervical screening runs every 3 years with cytology or every 5 years with high-risk HPV testing. That schedule does not tell a person whether a new partner transmitted HPV last month. Likewise, annual screening for sexually active gay and bisexual men is a public health rhythm, not a 12-month guarantee.
Access limits the science. Some clinics lack PCR for HSV, resistance testing for Mycoplasma genitalium, or darkfield microscopy for syphilis. A test that is unavailable is not a test that is negative. Ask what was tested, what was not, and when to repeat the test. That three-part question is the most useful limitation check in sexual health.