Several sexually transmitted infections cause swollen lymph nodes, most commonly in the groin. The main culprits are syphilis, genital herpes, HIV, lymphogranuloma venereum (LGV), and chancroid. Each one affects your lymph nodes differently, and the way the swelling feels, where it shows up, and whether it hurts can actually help narrow down which infection is involved.
Why STIs Cause Lymph Node Swelling
Lymph nodes are small filtering stations throughout your body that trap and fight infections. When a sexually transmitted pathogen enters through the genitals, mouth, or rectum, the nearest lymph nodes ramp up their immune response and swell. For genital infections, this typically means the inguinal nodes, the clusters in your groin crease. Some STIs stay localized there, while others spread through the lymphatic system and cause swelling in multiple areas of the body.
The character of the swelling tells a lot. Painless, rubbery nodes point toward one set of infections. Tender, inflamed nodes that may fill with pus point toward another. Understanding these differences helps make sense of what your body might be reacting to.
Syphilis
Syphilis is one of the most reliable causes of swollen groin nodes, and the swelling changes as the infection progresses through stages.
In primary syphilis, a painless sore called a chancre appears at the site of infection. Up to 80% of people in this stage develop regional lymph node swelling. The nodes feel rubbery and firm but are characteristically painless, and they can appear on both sides of the groin. Because neither the sore nor the swelling hurts, many people don’t notice them or don’t think they need attention.
In secondary syphilis, which develops weeks to months later, the infection has spread through the bloodstream. Lymph node swelling becomes more generalized and can appear in the neck, armpits, and other areas alongside a body rash, fever, and fatigue. The enlarged nodes at this stage are firm and rubbery with only minimal tenderness.
Genital Herpes (HSV)
Genital herpes commonly causes swollen, tender groin nodes, especially during a first outbreak. Unlike syphilis, the swelling is painful. A first episode of herpes tends to be the most intense, with clusters of blisters or open sores along with fever and noticeably sore lymph nodes in the groin. Later outbreaks are usually milder but can still trigger some node swelling alongside recurring sores. The swelling typically resolves as the outbreak clears, usually within two to three weeks for a first episode.
Lymphogranuloma Venereum (LGV)
LGV is caused by specific strains of chlamydia and produces some of the most dramatic lymph node swelling of any STI. It’s less common than standard chlamydia but is increasingly recognized, particularly among men who have sex with men.
The infection often begins with a small genital ulcer that heals on its own and goes unnoticed. Weeks later, the inguinal and femoral lymph nodes become firm, swollen, and intensely sore. This painful swelling is often the first symptom that drives someone to seek care. The affected nodes are typically on one side only. In severe cases, they can form large, pus-filled masses called buboes that may drain through the skin.
LGV can also spread through the lymphatic system and cause bodywide symptoms: fever, chills, muscle aches, joint pain, and general malaise. Depending on where the initial infection took hold, it can involve lymph node chains in the groin, pelvis, or even deeper in the abdomen. Left untreated, it can progress to chronic scarring, fistulas, and permanent tissue damage. Swollen nodes from LGV resolve with antibiotics, but large buboes sometimes need to be drained even after treatment has cleared the underlying infection.
Chancroid
Chancroid causes deep, painful genital ulcers along with tender, swollen groin nodes. The lymph node involvement occurs in fewer than half of cases, but when it does develop, it can be severe. The nodes can become suppurative, meaning they fill with pus and may form buboes similar to LGV. In advanced cases, these can lead to scarring or fistulas even after successful antibiotic treatment. Chancroid is rare in the United States and most high-income countries but remains a concern in parts of sub-Saharan Africa and the Caribbean.
HIV
Acute HIV infection, the period shortly after the virus enters the body, frequently causes swollen lymph nodes as part of a flu-like illness. Symptoms appear one to four weeks after exposure and last a median of about two weeks. Between 10% and 60% of people with acute HIV develop lymph node swelling, along with varying combinations of fever, rash, sore throat, mouth ulcers, and fatigue.
Unlike the STIs above, HIV-related swelling isn’t limited to the groin. It often affects multiple lymph node groups throughout the body, including the neck and armpits. This pattern of widespread swelling combined with a rash that can extend to the palms and soles is a hallmark of acute HIV. The initial symptoms resolve on their own, but without testing, the infection goes undetected and continues to progress. Persistent, generalized lymph node swelling can also occur in later stages of untreated HIV as the immune system becomes increasingly compromised.
How to Tell Them Apart
The feel and behavior of swollen nodes offer useful clues, though testing is always needed for a definitive answer.
- Painless, rubbery nodes with a painless sore: strongly suggests syphilis.
- Tender groin nodes with painful blisters or sores: typical of genital herpes.
- Severely painful, one-sided groin swelling with possible draining: characteristic of LGV.
- Tender, pus-filled groin nodes with deep painful ulcers: points toward chancroid.
- Widespread swelling in multiple body areas with flu-like symptoms: consistent with acute HIV.
One STI worth mentioning for its absence from this list: granuloma inguinale (donovanosis) causes genital ulcers but notably does not produce inguinal lymph node swelling, which can help rule it out.
What Happens After Treatment Starts
For bacterial STIs like syphilis, LGV, and chancroid, antibiotics clear the underlying infection, and lymph node swelling gradually subsides. Ulcers and general symptoms tend to improve faster than the nodes themselves. Large, fluid-filled nodes from LGV or chancroid can be slow to resolve and may need to be drained with a needle or small incision even when the infection is responding to treatment.
For genital herpes, antiviral medication shortens outbreaks and reduces symptom severity, including node swelling. The swelling recedes as each outbreak resolves. With HIV, starting antiretroviral therapy controls the virus and allows the immune system to stabilize, which resolves the persistent swelling seen in untreated infection.
If swollen groin nodes persist for more than a few weeks, don’t respond to treatment, or appear without other obvious STI symptoms, other causes beyond STIs need to be considered. Infections unrelated to sexual contact, autoimmune conditions, and rarely cancers like lymphoma can all cause inguinal swelling.