What Types of STDs Cause Ulcerations?

The STIs most likely to cause genital ulcers or sores are genital herpes, syphilis, and chancroid. Herpes and chancroid sores are usually painful; the syphilis sore is classically painless. Friction, trauma, and aphthous ulcers cause sores too, so not every sore is an infection. Only a test can tell them apart reliably.

Quick answer: the short list of likely causes

When someone shows up with a new sore "down there," three sexually transmitted infections sit at the top of the list, plus a handful of non-STI explanations. This is the working list a clinician runs through:

• Genital herpes (HSV-1 or HSV-2): clusters of small blisters that break into painful, shallow sores.
• Syphilis: a single (sometimes more) firm, round, painless sore called a chancre.
• Chancroid: deep, painful ulcers with tender, swollen lymph nodes in the groin (now rare in the U.S.).
• Non-STI causes: friction or trauma from sex, shaving, or tight clothing, and aphthous (canker-type) ulcers.

The single most useful clue you can gather at home is whether the sore hurts. Painful points toward herpes or chancroid; painless points toward syphilis. That split is a starting hypothesis. These conditions overlap too much by sight to call without a test.

Which STIs cause genital ulcers or sores

Genital herpes

Genital herpes is caused by two related viruses, herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2) CDC. Most people with herpes have no symptoms or symptoms so mild they never notice, and the majority of HSV-2 infections go undiagnosed. The absence of an obvious sore doesn't rule it out.

When a first outbreak does happen, it tends to be the worst one. Small blisters appear on or around the genitals, rectum, or mouth, then break open into shallow, painful sores that take a week or more to crust over and heal. Many people also feel sick during that first episode: fever, body aches, and swollen glands, similar to the flu. Repeat outbreaks are typically shorter and milder, and some people get a warning "prodrome" beforehand: tingling, itching, or a burning feeling in the spot where a sore is about to show up. That prodrome is your cue to start treatment early if you take suppressive or episodic medication.

Syphilis

Syphilis is caused by the bacterium Treponema pallidum, and it's curable with the right antibiotics CDC. The hallmark of the primary stage is a chancre: one or more painless, firm, round sores at the exact spot the bacteria entered the body: the penis, vagina, anus, rectum, lips, or mouth. Because it doesn't hurt and often sits somewhere out of view, the chancre is easy to miss entirely.

That sore appears about three weeks after exposure on average, though the incubation window runs anywhere from a week and a half to roughly three months. The chancre then lasts a few weeks and heals on its own, with or without treatment. That spontaneous healing traps people. The sore goes away, people assume the problem did too, but untreated syphilis quietly moves into a secondary stage with a rough red or reddish-brown rash (which can appear on the palms and soles), mucous-membrane lesions, fever, swollen lymph nodes, sore throat, patchy hair loss, and fatigue. To understand how the stages unfold, see syphilis overview.

Chancroid

Chancroid is a bacterial STI caused by Haemophilus ducreyi, and it's a classic cause of painful genital ulcers CDC, 2021. It has become rare in the United States, so it's lower on the list, but its pattern is distinctive. People develop one or more deep, painful ulcers, paired with tender, swollen, pus-filled lymph nodes in the groin. Unlike the painless syphilis chancre, the chancroid ulcer hurts. For the full picture of how it presents, see chancroid symptoms.

When it's NOT an STI

Plenty of genital sores have nothing to do with an infection. Friction and trauma are common culprits: vigorous sex, a snug seam, a shaving nick, or skin chafing can all leave a raw, tender spot that looks alarming but heals on its own. Aphthous ulcers, the same kind of "canker sore" some people get in their mouths, can also show up on genital skin and aren't sexually transmitted at all. Trauma and aphthous sores can be painful too, so pain alone doesn't prove it's an STI. You can't sort this out by staring at it.

How to tell them apart

Clinicians lean on a few discriminating features, even though none is definitive on its own:

• Pain: painful favors herpes or chancroid; painless favors syphilis.
• Number and look: herpes tends toward clustered small blisters that become shallow sores; syphilis is usually one firm, clean-edged round sore; chancroid is one or more deep, ragged, painful ulcers.
• Lymph nodes: tender, pus-filled groin nodes point toward chancroid; herpes may cause swollen glands during a first outbreak; the syphilis chancre is often accompanied by firmer, non-tender nodes.
• Whole-body symptoms: flu-like illness suggests a first herpes outbreak; a rash on palms and soles weeks later suggests secondary syphilis.

These patterns overlap, several of these infections are frequently silent, and the textbook "painless = syphilis" rule fails often enough that you shouldn't bet your health on it. A test settles which one (if any) it is. The appearance of the sore won't.

Side-by-side comparison

How it's tested

Each cause has its own test. With a herpes sore present, the best approach is a type-specific virologic swab of the lesion, a NAAT or culture taken directly from the sore CDC. Syphilis is diagnosed with two blood (serologic) tests run together: a nontreponemal test such as RPR or VDRL plus a treponemal test such as TP-PA, FTA-ABS, EIA, or CIA CDC, 2024. Chancroid is usually a probable diagnosis, a painful ulcer with the typical look plus negative syphilis and herpes testing, because confirming H. ducreyi needs a special culture medium that most labs don't stock.

In practice, testing is straightforward: a urine sample, a self-collected swab, or a quick exam depending on what's suspected, with results usually back in a few days. It's free or low-cost at health departments, Planned Parenthood, and Title X clinics. If you have an active sore, get seen while it's there, a swab of an open lesion is far more reliable than testing after it heals. See how to get tested, and if your exposure was recent, check when to test after exposure so you don't test too early to catch it.

What to do next

Don't try to self-diagnose from a photo or a symptom checklist; overlapping symptoms mean a test beats a guess. Avoid sexual contact until you've been evaluated, since ulcers of any cause make it much easier to pass or catch an infection. Syphilis and chancroid are bacterial and curable with the right antibiotics. Herpes isn't cured, but outbreaks are managed with antiviral medication, and some people explore alternative herpes treatments alongside standard care CDC. Your clinician will match the treatment to whatever the test shows.

Red flags, when to get seen urgently

• A sore that won't heal, keeps spreading, or comes back repeatedly.
• Fever, severe pain, or rapidly swelling, pus-filled lymph nodes in the groin.
• A rash on your palms or soles, especially with fever or hair loss, a possible sign of secondary syphilis.
• Trouble urinating, severe pain, or inability to pass urine during a first herpes outbreak.
• You're pregnant and develop any genital sore, get evaluated promptly to protect the pregnancy.
• You know a partner has syphilis, herpes, or any STI, get tested even if you feel fine.

Keep exploring on EasySTD: telling recent partners, confidential testing by state and Chancroid testing.