Genital sores or ulcers most often point to one of three sexually transmitted infections: genital herpes (HSV-1 or HSV-2), syphilis, and — rarely in the US — chancroid. The fastest clue is pain. Herpes and chancroid sores hurt; the classic syphilis chancre is painless. Friction, trauma, and canker-type ulcers can mimic all of these, so a test settles what your eyes can't.
painful blisters that crust over; tends to recur
a single painless sore (chancre); later a body rash
painful, soft, ragged ulcer(s)
| Item | Value |
|---|---|
| Genital herpes | managed — painful blisters that crust over; tends to recur |
| Syphilis | curable — a single painless sore (chancre); later a body rash |
| Chancroid | curable — painful, soft, ragged ulcer(s) |
Which STIs cause genital sores or ulcers
Three infections account for almost all STI-related genital ulcers, and each has a tell-tale pattern. Knowing those patterns helps you decide how urgently to act. But none is reliable enough to diagnose yourself: the appearances overlap, and several can be silent.
Genital herpes (HSV-1 and HSV-2)
Genital herpes is caused by two viruses, herpes simplex virus type 1 and type 2 CDC, herpes. Most people have no symptoms or very mild ones, most don't know they carry it, and the majority of HSV-2 infections are never diagnosed. A normal-looking exam doesn't rule it out.
When a first outbreak does show up, it usually starts as small blisters that break open into painful sores, which take a week or more to heal. Many people also feel flu-like — fever, body aches, swollen glands. The sores appear on or around the genitals, the rectum, or the mouth. Later outbreaks tend to be shorter and milder, and some people get a warning prodrome (tingling, itching, or burning in the area) a day or so before the sores appear.
There's no cure, but daily or episodic antiviral medicine controls outbreaks well; some people also ask about alternative herpes treatments to manage symptoms alongside standard antivirals.
Syphilis
Syphilis is caused by the bacterium Treponema pallidum and is curable with the right antibiotics CDC, syphilis. Its first sign runs opposite to herpes: a painless, firm, round sore called a chancre, appearing right where the bacteria entered — the penis, vagina, anus, rectum, lips, or mouth. There may be one or several.
The chancre shows up about three weeks after exposure, with an incubation range of roughly ten to ninety days. It lasts a few weeks and then heals on its own, treated or not. That self-healing is dangerous, because people think the problem is gone while the infection moves silently into the secondary stage: a rough red or reddish-brown rash that can land on the palms and soles, along with mucous-membrane sores, fever, swollen lymph nodes, sore throat, patchy hair loss, headache, weight loss, muscle aches, and fatigue.
Because untreated syphilis can pass to a baby, screening during pregnancy matters a great deal — see our guide to syphilis in pregnancy.
Chancroid
Chancroid is a bacterial STI caused by Haemophilus ducreyi and has become rare in the United States. It produces one or more deep, painful genital ulcers together with tender, swollen, pus-filled lymph nodes in the groin CDC, 2021. The chancroid ulcer hurts, while the syphilis chancre does not. You can read more about the look and course of chancroid symptoms if it's on the table for you.
When it's not an STI
Not every genital sore comes from sex. Friction or trauma — from vigorous sex, shaving, tight clothing, or scratching — can leave raw spots or shallow tears that look alarming but heal quickly. Aphthous ulcers, the same canker sores some people get in their mouths, can also appear in the genital area and aren't infectious at all.
These benign causes can look just like the serious ones, so nobody should call off a test because a sore "seems like just irritation."
How to tell them apart
The single most useful question is whether the sore is painful. Painful ulcers steer you toward herpes or chancroid; a painless one toward the syphilis chancre. A few more discriminating features help:
- Herpes tends to start as a cluster of small blisters that break into sores, often with a first-time flu-like feeling and recurring episodes over time.
- The syphilis chancre is usually a single firm, round, painless sore that heals on its own; the lack of pain is the giveaway.
- Chancroid causes deeper, ragged, painful ulcers paired with swollen, tender, pus-filled groin glands.
- Friction or canker-type sores often track with an obvious trigger (a recent shave, rough sex) and lack the systemic symptoms above.
Even so, these patterns overlap too much to trust by sight, and several of these infections are frequently silent. You usually can't self-diagnose this, and a test is what turns a guess into an answer.
Genital ulcer causes side by side
| Cause | Pain | Typical look | Timing / course | Other clues |
|---|---|---|---|---|
| Genital herpes | Painful | Cluster of blisters that break into sores | First outbreak heals in a week or more; recurs | Flu-like feeling first time; possible prodrome |
| Syphilis (primary) | Painless | Firm, round chancre, often single | Appears ~3 weeks after exposure; heals on its own | Later rash on palms/soles if untreated |
| Chancroid | Painful | Deep, ragged ulcer(s) | Rare in the US | Tender, pus-filled swollen groin glands |
| Friction / trauma | Variable | Raw spot or shallow tear | Heals quickly | Recent shaving, tight clothing, rough sex |
| Aphthous (canker) ulcer | Painful | Shallow ulcer with a pale base | Self-limited | Not infectious; may also occur in the mouth |
How it's tested
When a sore is present, the lab work depends on what's suspected. Herpes is confirmed by a swab of the lesion using type-specific virologic testing — NAAT or culture — and swab-based tests work best when there's an active sore CDC herpes testing. Syphilis takes two blood tests run together: a nontreponemal test (RPR or VDRL) plus a treponemal test (TP-PA, FTA-ABS, EIA, or CIA) CDC MMWR, 2024. Chancroid is usually a probable diagnosis — painful ulcers with a typical look and negative herpes and syphilis testing — because the definitive culture media for H. ducreyi isn't widely available.
In practice, testing is straightforward: a urine sample, a self-collected swab, or a quick exam depending on what's suspected, often free or low-cost at health departments, Planned Parenthood, and Title X clinics, with results usually back in a few days. For the full walk-through, see how to get tested.
What to do next
Don't wait for a sore to heal before getting checked. Herpes and especially syphilis can vanish on their own and still be infectious and progressing. If you've had a recent exposure, timing matters because blood tests need a window to turn positive; our guide on when to test after exposure explains it. All three of these infections are treatable: syphilis and chancroid are curable with antibiotics, and herpes is well controlled with antivirals. Avoid sexual contact until you've been evaluated, and let recent partners know so they can get checked too.
Red flags — get seen urgently
- Severe pain, spreading redness, or pus draining from a sore or a groin gland.
- Fever, swollen lymph nodes, or a rash on the palms and soles along with the sore.
- Trouble urinating, or sores so painful you can't pass urine.
- A painless sore you're tempted to ignore. That's the classic syphilis pattern and needs testing now, not later.
- You're pregnant and notice any genital sore — get evaluated promptly to protect the baby.