What Types of STDs Cause Genital Swelling?

Genital swelling can come from a few sexually transmitted infections, genital herpes, chancroid, and lymphogranuloma venereum (LGV), but it's just as often something that isn't an STI at all, like an allergic reaction, a cyst, or a blocked gland. Because these causes look so much alike, a test is what tells you which one you're dealing with.

The short list of likely causes

When people notice swelling in the genitals or groin, the usual suspects fall into two camps. On the STI side, the classic culprits are herpes (swollen glands and sores), chancroid (painful ulcers with tender, pus-filled groin nodes), and LGV (one-sided groin swelling that can balloon into a bubo). On the non-STI side, swelling can come from an allergic reaction, a cyst, or a blocked gland, none of which you caught from a partner CDC. You can't reliably tell them apart by looking, so the rest of this article walks through how a clinician sorts it out.

Which STIs cause genital swelling

Genital herpes

Genital herpes is caused by two viruses, herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2). Most people who carry it have no or very mild symptoms and never know they're infected; the majority of HSV-2 infections go undiagnosed CDC. The swelling people associate with herpes usually isn't the genital skin itself but the lymph glands. A first outbreak can bring flu-like symptoms, fever, body aches, and swollen glands, alongside the hallmark blisters that break open into painful sores and take a week or more to heal. Those sores can appear on or around the genitals, rectum, or mouth. Repeat outbreaks tend to be shorter and milder, and some people get a warning prodrome, a tingle or ache, before sores show up. If you've had recurrent herpes and want to talk through suppression and over-the-counter or complementary options, see alternative herpes treatments.

Chancroid

Chancroid is a bacterial STI caused by Haemophilus ducreyi, and its calling card is the combination of one or more deep, painful genital ulcers with tender, swollen, pus-filled lymph nodes in the groin CDC, 2021. Pain tells it apart: unlike the painless chancre of syphilis, a chancroid ulcer hurts. It's become rare in the United States, so most U.S. clinicians won't see it often, which makes it easy to miss. For a fuller breakdown of the ulcer-plus-node pattern and how it evolves, read about chancroid symptoms.

Lymphogranuloma venereum (LGV)

LGV is an aggressive form of chlamydia caused by Chlamydia trachomatis serovars L1, L2, or L3: different from the strains behind ordinary genital chlamydia, and far more inflammatory. It shows up in two ways. The more common presentation today is proctocolitis from rectal infection: mucoid or bloody rectal discharge, anal pain, constipation, fever, or tenesmus (a constant urge to pass stool even when the rectum is empty); outbreaks have clustered among men who have sex with men, often alongside HIV CDC. The second presentation is the one that drives people to search for swelling: tender, usually one-sided swelling of the groin lymph nodes (inguinal or femoral) that can progress to buboes: fluctuant, pus-filled lumps. That groin picture is more common among heterosexual patients. The full symptom timeline is covered in lgv symptoms.

When it's NOT an STI

Plenty of genital swelling has nothing to do with sex. An allergic reaction, to a new soap, latex condom, lubricant, or laundry detergent, can puff up the skin quickly, often with itching and redness rather than ulcers. A cyst, such as a Bartholin's gland cyst near the vaginal opening, forms when a gland's duct gets blocked and fluid backs up, producing a tender lump on one side. A blocked or inflamed gland anywhere in the genital area can do the same. None of these are contagious, and several STIs are frequently silent, so the symptom alone can't settle the question.

How to tell them apart

You usually can't tell by sight. The conditions overlap too much, and the quiet ones leave no clue at all. Still, a clinician leans on a handful of discriminating features:

• Painful sores plus flu-like body aches and tender glands point toward a first herpes outbreak.
• Deep, painful ulcers paired with pus-filled groin nodes raise the question of chancroid.
• One-sided groin swelling that turns into a fluctuant bubo, especially with rectal symptoms, suggests LGV.
• Itchy, red, fast-onset swelling after a new product points away from infection and toward an allergy.
• A soft, tender lump on one side near the vaginal opening, with no ulcer, is often a cyst or blocked gland.

These are clues, not verdicts. The symptoms overlap enough that a test is what turns a guess into an answer.

Side-by-side comparison

How it's tested

Testing depends on what's suspected: a urine sample, a self-collected swab, or a quick exam. With herpes, a clinician confirms it by swabbing an active lesion for type-specific virologic testing (NAAT or culture), which works best while sores are present CDC. Chancroid is usually a probable diagnosis, painful ulcers with the typical look, plus negative syphilis and herpes tests, because the definitive culture for H. ducreyi needs special media that isn't widely available. LGV is diagnosed by clinical suspicion plus a chlamydia NAAT taken right at the symptomatic site, such as the rectum, with other causes ruled out. You can usually get tested for free or low cost at health departments, Planned Parenthood, and Title X clinics, with results back in a few days.

What to do next

If you have unexplained genital swelling, get it checked rather than waiting it out. A quick visit sorts out whether it's an STI, a cyst, or an allergy, and each has a different fix. Most bacterial STIs clear with the right antibiotics, and herpes is managed with antiviral medicine. Timing matters too: if a recent exposure is the worry, knowing when to test after exposure keeps you from testing too early and getting a falsely reassuring result.

Red flags, when to get seen urgently

• Rapidly spreading swelling with severe pain or fever.
• A groin lump that becomes hot, fluctuant, or starts draining pus (a possible bubo).
• Inability to urinate or pass stool because of pain or swelling.
• Swelling along with bloody rectal discharge or anal pain.
• Any swelling in someone who is pregnant, immunocompromised, or living with HIV.
• Sudden, severe swelling after a new medication, food, or product, which can signal a serious allergic reaction.

Keep exploring on EasySTD: compare testing services, STD incubation periods and Chancroid testing.