Several STDs can cause lumps in the groin, but the most common culprits are lymphogranuloma venereum (LGV), chancroid, syphilis, and genital herpes. These lumps are usually swollen lymph nodes reacting to a nearby infection, though some STDs also cause bumps directly on the skin. The type of lump, whether it’s painful or painless, and what else is happening in the genital area can point toward a specific cause.
Why STDs Cause Groin Lumps
The groin contains clusters of lymph nodes that filter fluid from the genitals, upper legs, and lower abdomen. When an STD infects the genital area, these nodes often swell as the immune system responds. Doctors call this inguinal lymphadenopathy, and it can range from mildly enlarged, rubbery nodes you barely notice to large, painful masses called buboes that may fill with pus.
The key distinction is between swollen lymph nodes (lumps deep under the skin, near the crease of the groin) and skin-level bumps like blisters, warts, or raised papules that sit on or just below the surface. Both can feel alarming, but they point to different infections and need different treatment.
Lymphogranuloma Venereum (LGV)
LGV is caused by specific strains of chlamydia and produces some of the most dramatic groin lumps of any STD. The infection progresses in stages. First, a small painless sore or papule appears at the site of contact, often so subtle it goes unnoticed. Weeks later, the inguinal lymph nodes swell significantly, sometimes forming large, fluid-filled buboes that can rupture through the skin.
A classic physical finding is the “groove sign,” where swollen lymph nodes bulge on both sides of the inguinal ligament (the crease where your thigh meets your torso), creating a visible groove between them. Left untreated, LGV can become an invasive systemic infection, potentially causing chronic scarring, fistulas, and joint inflammation. It responds well to antibiotics when caught early, but the lymph node swelling can take weeks to fully resolve even after treatment starts.
Chancroid
Chancroid causes deep, painful genital ulcers alongside tender, swollen groin nodes. The combination of a ragged, soft ulcer and a painful lump in the groin is considered the hallmark of this infection. About half of people with chancroid develop significant lymph node swelling, and those nodes can fill with pus and become what’s known as suppurative buboes.
These buboes sometimes need to be drained with a needle or a small incision, even when antibiotics are working. The ulcers tend to heal faster than the lymph node swelling, so the groin lump may linger for a while after other symptoms improve. Without treatment, chancroid can cause permanent genital scarring.
Syphilis
Primary syphilis produces a distinctive pattern: a single painless ulcer (called a chancre) at the infection site, accompanied by swollen groin nodes on both sides. What sets syphilis apart is how the lumps feel. The lymph nodes are firm, only moderately enlarged, and completely painless. They don’t fill with pus or rupture.
The chancre typically appears 14 to 30 days after exposure and heals on its own within three to six weeks, which can create a false sense that the infection has resolved. The groin swelling often persists longer than the ulcer. This painless, bilateral pattern is easy to distinguish from the tender, pus-filled lumps of chancroid or LGV, but the lack of pain also means people sometimes ignore it until the infection progresses to its secondary stage.
Genital Herpes
A first outbreak of genital herpes (usually HSV-2) causes tender, swollen groin nodes in roughly 80% of cases. The swelling accompanies clusters of painful blisters or shallow ulcers on the genitals or anal area, along with flu-like symptoms: fever, body aches, headache, and fatigue in about two-thirds of people.
The lymph node swelling during a primary herpes outbreak is bilateral and tender to the touch. It typically resolves as the outbreak clears, usually within two to four weeks. Recurrent outbreaks are generally milder and less likely to cause noticeable groin swelling.
Skin-Level Bumps vs. Swollen Nodes
Not every groin lump involves lymph nodes. Some STDs cause raised bumps directly on the skin of the groin, inner thigh, or genital area that can be mistaken for deeper swelling.
- Genital warts from HPV appear as soft, flesh-colored growths that can be flat or raised with a cauliflower-like texture. They sit on the skin surface and don’t involve the lymph nodes.
- Molluscum contagiosum produces small, round, skin-colored or pinkish bumps, typically under a quarter inch across, each with a characteristic dimple or dot in the center. They can appear anywhere in the groin area and are sometimes itchy but not painful.
The simplest way to tell the difference: lymph node swelling feels like a marble or egg-sized lump deep under the skin near the groin crease, while skin-level bumps from warts or molluscum are visible on the surface and can be pinched between your fingers.
How to Tell STD Lumps From Other Groin Lumps
Groin lumps have plenty of non-STD causes, and a few physical clues help sort them out. An inguinal hernia, one of the most common causes of a groin lump, produces a bulge that becomes more noticeable when you stand up, cough, or strain, and may disappear when you lie down. Swollen lymph nodes from an STD don’t change with position or coughing. Hernias also have a softer, more diffuse feel compared to the firm, distinct shape of an enlarged lymph node.
Signs that point toward an STD as the cause include the presence of genital ulcers, sores, or blisters alongside the lump. Skin that looks inflamed or has a draining sinus over the node also suggests infection. A lump that appeared days to weeks after unprotected sexual contact, especially combined with any genital symptoms, warrants STD testing.
Symptoms That Need Prompt Attention
Certain patterns raise the urgency. Groin lumps that grow rapidly, feel hot to the touch, or develop overlying redness may indicate a bubo that’s about to rupture or an abscess forming. Fever and chills alongside a groin lump suggest the infection is spreading. Painful urination, genital discharge, or visible ulcers appearing with the lump all point toward an active STD that needs testing and treatment.
Lumps that are rock-hard, fixed in place (they don’t slide under your fingers), or accompanied by unexplained weight loss and night sweats can signal something other than an STD, including lymphoma or metastatic cancer, and need a different kind of evaluation. A lump that persists for more than two weeks without improvement, regardless of other symptoms, is worth getting checked.
Getting Tested and Treated
Because several STDs cause similar-looking groin lumps, accurate diagnosis requires testing rather than guessing based on appearance alone. A clinician will typically examine the lump and any genital lesions, then order blood tests, swabs, or urine tests depending on the suspected cause. In some cases, fluid may be drawn from a swollen node with a needle to identify the organism directly.
The good news is that the bacterial STDs most associated with groin lumps (LGV, chancroid, and syphilis) are all curable with antibiotics. Herpes isn’t curable, but antiviral treatment shortens outbreaks and reduces their frequency. Even when antibiotic treatment works quickly against the underlying infection, swollen lymph nodes in the groin can take several weeks to return to normal size. Large, pus-filled nodes sometimes need to be drained to heal properly, which is a minor in-office procedure.