Swollen lymph nodes in the groin from an STI most often point to genital herpes, syphilis, or early HIV, all of which can cause tender or swollen glands as the immune system reacts to infection. But not every case is an STI. Leg and skin infections also drain to the groin, and because these overlap, only a test settles which one it is.
Herpes simplex virus
Treponema pallidum
Human immunodeficiency virus
| Item | Value |
|---|---|
| Genital herpes | managed — Herpes simplex virus |
| Syphilis | curable — Treponema pallidum |
| HIV | managed — Human immunodeficiency virus |
Why STIs swell the lymph nodes in your groin
The lymph nodes in the crease of your groin (the inguinal nodes) filter fluid draining from the genitals, anus, and legs. When an infection takes hold in that territory, the nodes fill with immune cells fighting it off and grow larger, sometimes tender, sometimes firm, sometimes barely noticeable. Groin swelling is a downstream clue. Look at the pattern: whether the swelling is one-sided or on both sides, whether there's a sore nearby, and what else your body is doing.
Which STIs cause swollen lymph nodes in the groin
Genital herpes
Genital herpes is caused by two viruses, herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2) CDC, About Genital Herpes. Most people have no or very mild symptoms and never know they're infected, and the majority of HSV-2 infections go undiagnosed. When symptoms do show, a first outbreak can include flu-like illness with fever, body aches, and swollen glands, alongside blisters that break into painful sores. Those sores sit on or around the genitals, rectum, or mouth and take a week or more to heal. Painful sores with tender groin glands during a first episode is the typical pattern. Repeat outbreaks are shorter and milder, and some begin with a tingling or burning warning before lesions appear. For options beyond standard antivirals, see alternative herpes treatments.
Syphilis
Syphilis is caused by the bacterium Treponema pallidum and is curable with the right antibiotics CDC, About Syphilis. Its early sign looks the opposite of herpes: a primary chancre is one or more painless, firm, round sores at the site of infection, on the penis, vagina, anus, rectum, lips, or mouth. It appears about three weeks after exposure (the incubation range runs roughly 10 to 90 days) and heals on its own in three to six weeks whether or not it's treated. Swollen lymph nodes are common with that chancre, and they tend to be firm and painless too. If syphilis isn't caught, it moves to a secondary stage with a rough red or reddish-brown rash, classically on the palms and soles, plus fever, more widespread swollen lymph nodes, sore throat, patchy hair loss, headache, weight loss, muscle aches, and fatigue. Read more in what is syphilis? causes, stages & risks.
HIV
HIV is a virus that attacks the immune system, and swollen lymph nodes are a classic feature of its earliest phase CDC, About HIV. Within two to four weeks after infection, many people develop a flu-like illness called acute retroviral syndrome: fever, chills, rash, night sweats, muscle aches, sore throat, fatigue, mouth ulcers, and swollen lymph nodes hiv.gov. The swelling here is usually generalized, hitting neck, armpits, and groin together rather than confined to one groin. Some people have no symptoms at all, so testing is the only way to know, and these symptoms are easily mistaken for the flu or mono. After this acute phase, HIV often goes quiet for years (clinical latency) before, if untreated, advancing toward AIDS. Starting treatment early protects your health and stops transmission, see why earlier hiv treatment can help prevention.
When it's NOT an STI
Swollen groin glands often have nothing to do with sex. Ordinary skin and leg infections, an infected cut, an ingrown hair, athlete's foot, cellulitis, or even a stubborn blister on your foot, drain into the same inguinal nodes and can swell them. Two features push toward a non-STI cause: swelling on both sides at once (bilateral), which more often reflects a general or systemic process, and a single tender node paired with an obvious skin break or infection downstream on the same leg. None of this is something you can score reliably at home, so get checked.
How to tell them apart
You usually can't tell them apart by sight alone. These conditions overlap too much, and several are frequently silent. A few discriminating features help a clinician narrow it down before testing:
- Is there a sore, and does it hurt? Painful sores point toward herpes; a painless, firm sore points toward a syphilis chancre.
- One side or both? A single tender groin node with a nearby sore suggests a local STI or skin infection; swelling in the groin and neck and armpits together fits early HIV.
- Firm or tender? Herpes nodes are usually tender; syphilis nodes tend to be firm and painless.
- What else is happening? Widespread flu-like illness with rash and night sweats raises the question of acute HIV; a rash on the palms and soles is a hallmark of secondary syphilis.
- Any obvious skin or foot infection on that leg? That can explain swelling without any STI at all.
Side-by-side comparison
| Cause | Sore at the site? | Node character | Other clues | Timing after exposure |
|---|---|---|---|---|
| Genital herpes | Painful blisters that break into sores | Tender, often one side, mainly in first outbreak | Flu-like symptoms; prodrome before repeats; often silent | Not specified on current CDC pages |
| Syphilis | Painless, firm, round chancre | Firm, painless | Later: rash on palms/soles, fever, hair loss | Chancre ~3 weeks (range 10–90 days) |
| HIV (acute) | No genital sore; possible mouth ulcers | Generalized swelling (neck, armpits, groin) | Fever, rash, night sweats, sore throat, fatigue | Flu-like illness 2–4 weeks |
| Non-STI (skin/leg infection) | Cut, ingrown hair, athlete's foot, cellulitis | Tender; can be bilateral | Visible skin break or infection on the same leg | Varies with the local infection |
How it's tested
Testing turns a guess into an answer, matched to what's suspected. Herpes is confirmed when lesions are present by type-specific virologic testing of the sore, where a swab analyzed by NAAT or culture works best CDC, Herpes Testing. Syphilis needs two blood tests together: a nontreponemal test (RPR or VDRL) plus a treponemal test (TP-PA, FTA-ABS, EIA, or CIA) CDC, 2024. HIV has several options with different windows after exposure: a nucleic-acid test, a 4th-generation antigen/antibody lab test, and antibody or rapid tests CDC, HIV Testing. A negative is only conclusive after the test's window has passed with no new exposure during it. In practice, testing means a urine sample, a self-collected swab, or a quick exam, often free or low-cost at health departments, Planned Parenthood, and Title X clinics, with results usually back in a few days. You can get tested, and check when to test after exposure so you don't test too early.
What to do next
Don't try to self-diagnose from the swelling. Get checked, because the right treatment depends entirely on which infection (if any) it is. Syphilis is curable with antibiotics. Herpes is managed with antivirals that shorten and space out outbreaks. HIV is treated with daily medication that keeps you healthy and prevents passing it on. Bring up every symptom and any recent exposure with your clinician, and ask which tests you need based on timing.
Red flags — when to get seen urgently
Get medical care promptly, rather than waiting, if any of these are present:
- Skin over the swollen node that is red, hot, spreading, or breaking down, a possible abscess or cellulitis needing prompt care.
- Fever with rapidly enlarging or very painful groin swelling.
- A node that's growing fast, rock-hard, or fixed in place.
- A painless sore plus a rash on your palms and soles, a pattern that needs syphilis testing without delay.
- A flu-like illness with rash and night sweats in the weeks after a possible exposure, worth checking for acute HIV right away.