Short answer
Sexual health has a compact working vocabulary.
Once you know roughly thirty terms, what an STI is versus an STD, how screening differs from diagnosis, what test names actually measure, and what prevention tools do, every result letter, guideline, and article on this site reads clearly.
This glossary defines each term plainly, with examples of where you will meet it.
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STI vs STD
An STI (sexually transmitted infection) means a pathogen is present.
An STD (sexually transmitted disease) means the infection is causing symptoms or illness.
Every STD starts as an STI; most STIs never become STDs. Public health increasingly prefers STI because it covers silent infections.
See STD vs STI: what is the difference?
Bacterial, viral, and parasitic infections
Bacterial STIs (chlamydia, gonorrhea, syphilis) are curable with antibiotics.
Viral STIs (HIV, herpes, HPV, hepatitis B) are manageable but not curable. Treatment controls them.
Parasitic causes (trichomoniasis, pubic lice, scabies) are curable with targeted therapy.
Acute, chronic, and latent
- Acute describes a new, active phase (for example, a first herpes outbreak).
- Chronic describes a long-lasting state (for example, chronic hepatitis B).
- Latent describes a dormant phase with no symptoms but future reactivation possible (herpes latency between outbreaks; latent syphilis before tertiary disease).
Asymptomatic and subclinical
Asymptomatic means infected with no felt signs. The typical STI state, which is why screening matters more than symptom-watching.
Subclinical means measurable changes exist (for example, mild inflammation on exam) without symptoms the person notices.
Colonization vs infection
Colonization means organisms present without disease (for example, HPV detected without lesions).
Infection implies pathogen activity that may need management.
The line blurs in practice. Clinicians interpret context, not just test positivity.
Outbreak, prodrome, and shedding
An outbreak is a visible herpes episode.
Prodrome is the warning phase. Tingling, itching, or nerve pain hours to days before lesions.
Shedding (viral shedding) is release of infectious virus with or without symptoms; asymptomatic shedding causes most herpes transmission.
Anatomic syndromes: PID, cervicitis, urethritis, epididymitis
These name inflamed sites, not specific organisms.
- PID (pelvic inflammatory disease) affects uterus, tubes, and ovaries.
- Cervicitis affects the cervix.
- Urethritis affects the urethra.
- Epididymitis affects the sperm-carrying tube behind the testicle.
Each has STI and non-STI causes that testing sorts out.
Testing terms
Screening vs diagnostic testing
Screening looks for silent infection on a schedule (for example, yearly chlamydia screening).
Diagnostic testing investigates symptoms or known exposures.
The same technology serves either purpose; context changes interpretation and follow-up.
NAAT
Nucleic acid amplification testing detects pathogen DNA or RNA from urine or swabs.
It is the sensitive standard for chlamydia, gonorrhea, trichomoniasis, and herpes sores.
Example: “Your NAAT was positive for chlamydia” means bacterial DNA was found. Treatment follows.
Culture
Growing live organisms from a sample.
Slower than NAAT but reveals which drugs still work. Essential for drug-resistant gonorrhea and treatment failures.
Serology
Blood-test detection of antibodies (immune response) or antigens (viral pieces).
Treponemal tests confirm syphilis exposure ever; non-treponemal tests (RPR/VDRL) track active disease.
HIV antigen/antibody combination tests are the screening standard.
Window period
The gap between infection and detectability, different for every infection–test pair.
Testing inside the window can miss real infections. The reason for scheduled retests, not single early tests.
Sensitivity and specificity
Sensitivity is how well a test finds real infections (misses become false negatives).
Specificity is how well it clears the uninfected (false alarms become false positives).
No test scores perfectly on both, which is why confirmation steps exist.
Confirmatory testing
Second-stage verification after a reactive screen. For example, antibody-differentiation assays after a reactive HIV screen, or treponemal tiebreakers in syphilis testing.
Never act on a single unexpected screening result as final.
Test-of-cure vs retesting
Test-of-cure verifies treatment worked (select situations: pregnancy, persistent symptoms, throat gonorrhea).
Retesting (typically ~3 months after bacterial STIs) catches reinfection.
Different purposes, different schedules.
Self-collection
Patient-collected vaginal or rectal swabs, mailed or handed to labs.
Validated as accurate as clinician collection for covered infections. Distinct from rapid self-tests analyzed at home.
Treatment terms
First-line and alternative regimens
First-line therapy is the guideline-preferred treatment; alternatives apply with allergies, pregnancy, resistance, or availability issues.
Regimens evolve with resistance. Always confirm current guidance with a clinician rather than relying on memorized drug names.
Syndromic vs directed therapy
Syndromic therapy treats the likely causes of a syndrome immediately (for example, urethritis coverage before results).
Directed therapy targets the confirmed organism after results.
Good care usually starts syndromic and finishes directed.
Adherence
Taking medication exactly as prescribed. Full courses, correct intervals.
Partial adherence breeds treatment failure and antibiotic resistance.
Resistance
Bacteria evolving past antibiotics, notably gonorrhea and Mycoplasma genitalium.
Resistance is why regimens change over time, why cultures matter for failures, and why leftover-antibiotic self-treatment harms everyone.
EPT and partner services
EPT (expedited partner therapy) provides partners medication without a prior exam where legal.
Partner services (provider referral) has health-department staff notify partners discreetly.
Both break reinfection cycles.
Suppressive vs episodic therapy
Suppressive therapy is daily antivirals preventing most herpes outbreaks and cutting transmission.
Episodic therapy treats individual outbreaks at prodrome.
Choice follows frequency, severity, and transmission context.
ART and DAA
ART (antiretroviral therapy) suppresses HIV, usually as daily medication.
DAA (direct-acting antivirals) cure most hepatitis C in weeks.
Both transformed once-fatal infections into manageable or curable conditions.
Jarisch-Herxheimer reaction
Fever, chills, and aching within a day of first syphilis treatment, caused by dying organisms. Not an allergy.
It resolves with supportive care; pregnancy cases need monitoring.
Prevention terms
External and internal condoms, dams
External condoms cover the penis; internal condoms line the vagina or anus.
Dental dams cover vulva or anus during oral sex.
All are single-use barriers requiring correct consistent use.
PrEP, PEP, and doxy-PEP
PrEP is ongoing HIV prevention before exposure (daily pills or periodic injections).
PEP is emergency 28-day HIV treatment started within 72 hours after exposure.
Doxy-PEP is doxycycline after condomless sex preventing bacterial STIs in CDC-defined high-incidence groups.
U=U
Undetectable = Untransmittable: people with HIV maintaining undetectable viral loads do not transmit HIV sexually.
It covers sexual HIV transmission specifically. Not other STIs.
Vaccines: Gardasil 9, hepatitis A/B
Gardasil 9 prevents the HPV types behind most HPV cancers and warts.
Hepatitis B vaccine prevents a sexually transmissible liver infection.
Hepatitis A and mpox vaccines cover adjacent risks in specific populations.
Screening cadence and abstinence windows
Screening cadence is your personalized testing rhythm (yearly baselines to quarterly high-risk schedules).
Abstinence windows are the no-sex periods during and after treatment until all partners complete therapy with resolved symptoms.
Harm reduction and syringe services
Practical strategies reducing drug-related harms without requiring abstinence: never sharing injection equipment, syringe service programs providing sterile supplies plus testing linkage, and naloxone carriage.
People-first language
Use person-first, nonjudgmental terms site-wide: person with herpes or HIV (never labels), tested/positive/treated (never “clean/dirty”), acquired or transmitted (never “caught”), sex worker (never slurs).
Language shapes whether people test, disclose, and treat. It is a care intervention, not politeness.
When to seek care
Whenever unfamiliar terms appear in results or guidance. Ask clinicians to translate, and revisit this glossary as a living reference.
If a term on this page seems outdated, report it via the contact page so editorial review can correct it.