Short answer

Groin lymph nodes drain the genitals, so genital infections swell them. But so do skin infections, systemic viruses, hernias, and malignancies.

Sorting STI causes (chancroid buboes, LGV, herpes, syphilis) from the rest runs on node character plus genital findings: tenderness, size, fluctuation, groove signs, and what the genital exam shows alongside.

Swollen groin nodes with genital sores, discharge, or exposure history get STI workups promptly; other patterns widen testing appropriately.

Continue with Testicular Pain and Possible Infections and Mouth Sores and Sexually Transmitted Infections for the directly connected guidance.

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STI patterns with their signatures

  • Chancroid: unilateral tender bubo that may rupture. With a soft painful ragged ulcer as the source lesion. Rare in the US, unmissable when present.
  • LGV: tender nodes with the groove sign (nodes above and below the inguinal ligament creating a visible furrow), appearing weeks after a fleeting sore that patients often forget.
  • Herpes: bilateral small tender nodes accompanying outbreaks. Modest swelling compared to bubo diseases.
  • Syphilis: classically painless firm nodes with chancre or rash. Painlessness misleads toward non-urgency, wrongly.

Non-STI patterns with their signatures

  • Bacterial skin infections and folliculitis: tender nodes draining an obvious skin source.
  • Cat-scratch disease: regional nodes weeks after feline contact.
  • EBV/CMV mononucleosis and toxoplasmosis: generalized nodes with systemic illness.
  • Lymphoma: rubbery, prolonged, painless enlargement with systemic symptoms (fevers, night sweats, weight loss). The pattern demanding biopsy, not antibiotics.
  • Hernias: reducible bulge worsening with strain, not a node at all. Cough impulse distinguishes.
  • Lipomas: soft, mobile, chronic, painless lumps.

Evaluation sequence

Genital examination with sore swabs (source lesions explain nodes).

Syphilis and HIV serology (systemic STI context).

Node examination documenting size, tenderness, fluctuation, and groove sign. Ultrasound distinguishing abscess (drainable) from solid node (biopsy-considered).

Biopsy for persistent unexplained enlargement beyond weeks. Lymphoma exclusions can’t wait on antibiotic trials.

Care by cause

STI-directed antibiotics with bubo aspiration (needle drainage, never incision. Incision creates chronic sinus tracts) when fluctuant.

Non-STI causes follow their own pathways (dermatologic, oncologic, hernia repair).

All presentations get STI source testing regardless. Coexisting causes occur, and missing an STI while treating lymphoma (or vice versa) harms doubly.

When to seek care

Promptly for groin swelling with sores, discharge, or exposure history.

Urgently for rapidly enlarging painful swelling with fever (abscess or severe adenitis).

Electively but firmly for persistent painless enlargement. The lymphoma rule-out that patience doesn’t serve.