Syphilis, herpes, and chancroid all cause genital sores, but the classic split is pain and depth: a syphilis chancre is a single firm, painless ulcer; herpes makes clusters of small painful blisters that crust over; chancroid produces deep, ragged painful ulcers with tender, pus-filled groin nodes. Overlap is common, so testing settles it.
Haemophilus ducreyi
Treponema pallidum
Herpes simplex virus
| Item | Value |
|---|---|
| Chancroid | curable — Haemophilus ducreyi |
| Syphilis | curable — Treponema pallidum |
| Genital herpes | managed — Herpes simplex virus |
What each one is
Chancroid
Chancroid is a bacterial STI caused by Haemophilus ducreyi, a classic cause of painful genital ulcers CDC chancroid, 2021. It has become rare in the United States, so clinicians don't expect it and it gets missed. The hallmark is one or more deep, painful ulcers paired with tender, swollen, pus-filled lymph nodes in the groin (sometimes called buboes, which are abscessed nodes that can rupture). For the full picture of how the sores and swelling present, see our guide to chancroid symptoms.
Syphilis
Syphilis is caused by the spiral-shaped bacterium Treponema pallidum and is curable with the right antibiotic CDC syphilis. It moves through stages. The primary stage is a painless, firm, round sore (a chancre) at the spot where bacteria entered — penis, vagina, anus, rectum, lips, or mouth — and it heals on its own whether or not you treat it, which fools people into thinking the problem went away. The infection is still there. For how the later stages unfold and who's at risk, read what is syphilis? causes, stages & risks.
Genital herpes
Genital herpes is a viral infection caused by herpes simplex virus type 1 (HSV-1) or type 2 (HSV-2) CDC genital herpes. Most people have no symptoms or very mild ones, and the majority of HSV-2 infections are undiagnosed because people simply don't know they carry it. When symptoms do appear, they recur: the virus stays in nerve roots for life and reactivates periodically rather than being cleared.
Symptoms compared
The lesion itself is the first clue, even though it's not definitive:
- Chancroid: one or several deep, painful, soft-edged ulcers, usually with tender, swollen groin nodes that can fill with pus.
- Syphilis (primary): typically a single painless, firm, round chancre that lasts 3–6 weeks and heals with or without treatment.
- Syphilis (secondary): after the chancre fades, a rough red or reddish-brown rash — often 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.
- Genital herpes (first outbreak): blisters that break into painful sores taking a week or more to heal, often with flu-like fever, body aches, and swollen glands. Repeat outbreaks are shorter and milder, and many people feel a tingling or burning prodrome first.
In practice the symptoms overlap enough that you usually can't tell these apart by how the sore feels. A test settles it.
How to tell them apart
Clinicians lean on a few discriminating features while waiting for results. Pain and number help: the syphilis chancre is classically painless and usually solitary, whereas chancroid is painful and the groin nodes are tender and may suppurate. Herpes presents as a cluster of small vesicles that erode into shallow sores, not one deep crater. Timing matters too — herpes tends to recur in the same area, while a primary syphilis chancre appears once and disappears. None of this is reliable enough to skip testing: secondary syphilis can mimic many rashes, and a herpes first episode can look alarming and ulcerative. Treat the appearance as a starting hypothesis.
Side-by-side comparison
| Chancroid | Syphilis (primary) | Genital herpes | |
|---|---|---|---|
| Cause | Haemophilus ducreyi (bacteria) | Treponema pallidum (bacteria) | HSV-1 or HSV-2 (virus) |
| Sore | Deep, ragged ulcer(s) | Firm, round chancre, usually single | Clusters of small blisters → shallow sores |
| Pain | Painful | Painless | Painful |
| Groin nodes | Tender, often pus-filled | May be firm, not tender | Tender during first outbreak |
| Course | Persists until treated | Heals on its own, then progresses | Recurs over a lifetime |
| Cure? | Yes — antibiotics | Yes — penicillin | No — antivirals control it |
Testing
Each infection has its own workup, and they're often run together because a sore could be any of them. Chancroid is largely a clinical diagnosis: a probable diagnosis is painful genital ulcers of typical appearance plus negative syphilis and herpes testing, while a definitive diagnosis needs H. ducreyi grown on special culture media that most labs don't stock. Syphilis requires two blood tests — a nontreponemal test (RPR or VDRL) and a treponemal test (TP-PA, FTA-ABS, EIA, or CIA) — because neither alone is conclusive CDC syphilis lab, 2024. For herpes when a sore is present, swab the lesion for type-specific virologic testing by NAAT or culture CDC herpes testing.
What testing looks like depends on what's suspected: a urine sample, a self-collected or clinician-collected swab, or a quick visual exam, often combined with a blood draw. It's free or low-cost at health departments, Planned Parenthood, and Title X clinics. If you have an active sore, don't wait for it to heal — swab-based tests work best while the lesion is fresh. You can get tested at a clinic or order a kit, and if you're counting days since a possible exposure, our guide on when to test after exposure explains why a too-early blood test can read negative.
Treatment compared
Two of these three are curable, and the regimens differ sharply. Chancroid is cured by a single dose — azithromycin 1 g orally or ceftriaxone 250 mg IM — with alternatives of ciprofloxacin 500 mg twice daily for 3 days or erythromycin base 500 mg three times daily for 7 days; a re-examination 3–7 days after starting therapy confirms the ulcer is improving.
Syphilis is still cured only by penicillin, and the dose follows the stage: primary, secondary, and early latent disease get one injection of benzathine penicillin G 2.4 million units IM, while late or unknown-duration disease needs three weekly injections CDC P&S syphilis. The correct product is benzathine penicillin G (Bicillin L-A). The combination Bicillin C-R is not an acceptable substitute and has caused real treatment-failure errors CDC syphilis treatment. Within a couple of hours of that first shot, roughly 95% of people treated for secondary syphilis get fever, chills, and headache — the Jarisch-Herxheimer reaction, which is dying bacteria releasing inflammatory signals rather than a penicillin allergy, and it usually settles within about a day StatPearls JHR.
Herpes can't be cured. Three FDA-approved antivirals — acyclovir, valacyclovir, and famciclovir — shorten and reduce outbreaks but don't clear the virus CDC herpes treatment. Daily suppressive therapy does more than calm your own symptoms: in a trial of serodiscordant couples, suppressive valacyclovir lowered the risk of passing HSV-2 to a partner by about 48% Corey et al.. Some people also ask about non-drug options; we cover the evidence in our piece on alternative herpes treatments.
Can you have more than one at once?
Yes — co-infection is real, and it's one reason testing matters even when a diagnosis seems obvious. Genital ulcers from any of these break the skin barrier and make it easier to acquire or transmit HIV and other STIs. People with HSV-2 shed virus on about 10% of days even with no outbreak, and most of that shedding leaves no visible sore JAMA HSV shedding, so a herpes infection can coexist silently with a syphilis chancre or a chancroid ulcer. When a sore won't fit one tidy diagnosis, clinicians test for all three rather than guess.
When to see a clinician
See a clinician promptly for any new genital sore, ulcer, or blister cluster — especially a painful ulcer with swollen groin nodes, a rash on the palms and soles, or a painless sore that came and went. Don't wait for it to heal on its own; the primary syphilis chancre disappears while the infection keeps advancing. Syphilis is climbing nationally, with about 53,000 primary-and-secondary cases reported in 2023 CDC AtlasPlus, 2023, so get a painless sore tested rather than watching it.