Syphilis and genital herpes both cause genital sores, but they're fundamentally different. Syphilis is a bacterial infection that produces a single painless, firm sore and is curable with penicillin. Herpes is a lifelong viral infection that causes painful, recurring blisters; antivirals control it but can't cure it. A swab or blood test tells them apart.
curable with penicillin; congenital cases surging
lifelong; antivirals control, not cure
| Item | Value |
|---|---|
| Syphilis | curable — curable with penicillin; congenital cases surging |
| Genital herpes | managed — lifelong; antivirals control, not cure |
What each infection is
Syphilis
Syphilis is caused by the bacterium Treponema pallidum, a corkscrew-shaped organism that enters through tiny breaks in skin or mucous membranes during sex CDC. Because it's bacterial, it's curable with the right antibiotic. Left untreated it moves through stages over months to years, and it's climbing fast in the U.S. — roughly 53,000 primary-and-secondary cases were reported in 2023, and the late or unknown-duration stage nearly doubled in rate between 2020 and 2023 CDC AtlasPlus, 2023.
Genital herpes
Genital herpes is caused by two viruses — herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2) CDC. Once you're infected, the virus stays in nerve roots for life and can reactivate periodically. Most people have no symptoms or symptoms so mild they go unnoticed, which is why the majority of HSV-2 infections are never diagnosed. There's no cure, but the infection is manageable and most people live with it without serious problems.
Symptoms compared
The classic syphilis sore is the chancre: one or more painless, firm, round ulcers that show up where the bacteria entered — penis, vagina, anus, rectum, lips, or mouth. A chancre lasts three to six weeks and heals on its own whether or not you treat it, which fools people into thinking the problem is gone. If untreated, syphilis can advance to a secondary stage with a rough red or reddish-brown rash that famously can appear on the palms and soles, plus mucous-membrane lesions, fever, swollen lymph nodes, sore throat, patchy hair loss, headache, weight loss, muscle aches, and fatigue.
Herpes feels different. A first outbreak typically brings clusters of blisters that break open into painful sores taking a week or more to heal, often with flu-like symptoms — fever, body aches, swollen glands. Sores appear on or around the genitals, rectum, or mouth. Recurrences are usually shorter and milder, and many people get a prodrome (a tingling, itching, or burning warning a day or so before sores appear). The hardest part to grasp: people with HSV-2 shed virus on about 10% of days even with no outbreak, and most of that shedding leaves no visible sore — which is exactly how it spreads unknowingly JAMA.
How to tell them apart
The single most useful clue is pain. A syphilis chancre is classically painless and firm; herpes sores are painful and start as fluid-filled blisters. Number and shape help too — syphilis tends to be one well-defined ulcer, while herpes usually appears as a cluster of small blisters that crust over. Timing differs: a chancre is solitary and heals quietly, whereas herpes comes in outbreaks that can return.
Here's the honest caveat: these features overlap enough that you usually can't tell them apart by feel, and a coinfection (especially with HIV) can blur the textbook picture. A test is what settles it — don't try to self-diagnose from a photo or a symptom checklist.
Syphilis vs herpes at a glance
| Syphilis | Genital herpes | |
|---|---|---|
| Cause | Bacterium (Treponema pallidum) | Virus (HSV-1 or HSV-2) |
| Classic sore | Painless, firm, usually single (chancre) | Painful blisters in clusters |
| Sore heals on its own? | Yes, but infection persists untreated | Yes, but virus stays and can recur |
| Recurs? | No — progresses through stages instead | Yes — repeat outbreaks |
| Main test | Two blood tests (nontreponemal + treponemal) | Swab of the sore (NAAT or culture) |
| Curable? | Yes — penicillin | No — antivirals control it |
Testing
The two infections are diagnosed in different ways. Syphilis is a blood diagnosis and requires two serologic tests to confirm — a nontreponemal test (RPR or VDRL) plus a treponemal test (TP-PA, FTA-ABS, EIA, or CIA) CDC Lab Recs, 2024. Neither one alone is enough, because each can give a false result on its own; using both together is what makes the diagnosis reliable.
Herpes is best confirmed by sampling an actual sore. When lesions are present, a type-specific virologic test of the lesion — by NAAT or culture — is the standard, and swab-based tests work best CDC. Blood antibody tests exist but are less useful for sorting out a current sore. In practice testing means a urine sample, a self-collected or clinician swab, or a quick exam depending on which infection is suspected — and it's free or low-cost at health departments, Planned Parenthood, and Title X clinics. You can also get tested through a confidential service, and if you're testing after a specific encounter, check when to test after exposure so you don't test too early to catch it.
Treatment compared
Syphilis is curable, and penicillin is still the only reliable cure — no oral drug dependably substitutes StatPearls. For primary, secondary, and early latent syphilis the treatment is benzathine penicillin G given as a single intramuscular injection; late or unknown-duration disease takes three weekly injections CDC Tx Guidelines. One safety point matters enormously: the correct product is benzathine penicillin G (Bicillin L-A). The combination product Bicillin C-R is not an acceptable substitute and has caused real treatment-failure errors CDC. Some people develop fever, chills, and headache within a couple of hours of the first shot — that's the Jarisch-Herxheimer reaction (dying bacteria releasing inflammatory signals, not a penicillin allergy), and it settles within about a day StatPearls.
Herpes can't be cured, but three FDA-approved antivirals — acyclovir, valacyclovir, and famciclovir — control symptoms and shorten outbreaks CDC. You can take them episodically at the first sign of an outbreak or daily as suppressive therapy. Daily suppression does more than reduce your own flare-ups: in a randomized trial of couples where one partner had HSV-2, suppressive valacyclovir lowered the risk of passing the virus to a partner by about 48% Corey et al.. If standard antivirals aren't a fit, here's an honest look at alternative herpes treatments and what the evidence does and doesn't support.
Can you have both at once?
Yes. Having one STI doesn't protect you from another, and genital ulcers from either infection can make it easier to acquire HIV and other infections through the same broken skin. Because the two can look similar and can coexist, a thoughtful clinician usually tests for several STIs together rather than guessing from a single sore. If you've got an ulcer that doesn't fit a clean textbook description, that's a reason to test broadly, not to assume.
When to see a clinician
See a clinician for any new genital sore, ulcer, blister, or unexplained rash — especially a rash on the palms or soles, which is a red flag for secondary syphilis. Get checked promptly if a partner tells you they've tested positive for either infection, even if you feel fine. And if you're pregnant or planning to be, syphilis screening is essential because untreated infection can be passed to the baby; here's what to expect with syphilis in pregnancy testing and treatment.