Lymphedema in the legs develops when the lymphatic system can’t drain fluid properly, causing it to pool in the tissues and produce persistent swelling. The causes fall into two broad categories: problems you’re born with (primary lymphedema) and damage from something external like surgery, cancer, infection, or obesity (secondary lymphedema). Secondary causes are far more common, especially in developed countries.
How Lymph Normally Drains From Your Legs
Your legs contain a network of lymphatic vessels organized into distinct groups that run along different sides of your lower leg and connect to lymph nodes in your groin and behind your knee. These tiny vessels collect excess fluid, proteins, and waste products from your tissues and push them upward toward your bloodstream. The system relies on muscle contractions, one-way valves inside the vessels, and the vessels’ own gentle squeezing action to keep fluid moving against gravity.
When any part of this drainage network gets blocked, damaged, or overwhelmed, fluid backs up into the tissues of your leg. Unlike ordinary water retention, lymph fluid is rich in protein, which draws even more fluid into the surrounding tissue over time and triggers inflammation. Left unmanaged, the stagnant protein-rich fluid causes the tissue to thicken and harden, making the swelling progressively harder to reverse.
Cancer Treatment and Surgery
The most recognized cause of leg lymphedema in Western countries is cancer treatment that involves removing or damaging lymph nodes. An inguinal lymphadenectomy (removal of lymph nodes in the groin) or a pelvic lymphadenectomy (removal of nodes in the upper pelvis) directly eliminates parts of the drainage pathway your legs depend on. The more nodes removed, the higher the risk.
Cancers of the vulva, vagina, ovaries, uterus, cervix, prostate, and colon or rectum are the types most likely to lead to leg lymphedema, because they sit near the lymph nodes and vessels that serve the lower body. Melanoma and sarcoma surgeries can also cause it when groin nodes are involved. Radiation therapy compounds the risk by scarring lymphatic tissue, and chemotherapy can further weaken the system. When surgery, radiation, and chemotherapy overlap, the chance of developing lymphedema rises substantially.
Lymphedema doesn’t always appear right after treatment. It can surface months or even years later, sometimes triggered by an injury, infection, or long flight that tips an already compromised system past its limit.
Cancer Itself
A growing tumor can physically block lymphatic vessels or nodes before any treatment begins. Cancers that form in the abdomen or genital area are especially likely to obstruct lymph flow to and from the legs. In some cases, new or worsening leg swelling is what prompts the diagnosis in the first place.
Obesity and Lymphatic Overload
Severe obesity is an increasingly recognized cause of leg lymphedema, and it can develop even without any prior surgery or cancer. Research published in the Journal of the American College of Surgeons found that patients who developed lower extremity lymphedema had an average BMI of 64, while obese patients without lymphedema averaged a BMI of about 39. A clear threshold appears to exist: once body mass climbs high enough, the sheer volume of tissue and the mechanical pressure on lymphatic vessels overwhelm the system’s capacity to drain fluid.
This form, sometimes called obesity-induced lymphedema, typically affects both legs and tends to improve with significant weight loss, though the lymphatic damage may not fully reverse if the condition has been present for a long time.
Chronic Venous Insufficiency
When the veins in your legs can’t pump blood back to your heart efficiently, the resulting backup of pressure eventually spills over into the lymphatic system. In severe cases, this creates a condition called phlebolymphedema, where vein blockages or backflow prevent the body from circulating lymphatic fluid. It’s essentially a one-two punch: the venous system floods the tissues with more fluid than normal, and the lymphatic system, now overloaded and sometimes damaged by the sustained pressure, can’t keep up.
Phlebolymphedema is common in people with long-standing varicose veins, a history of deep vein thrombosis, or other forms of chronic vein disease that have gone untreated for years.
Infections: Filariasis and Cellulitis
Globally, the single biggest cause of leg lymphedema is a parasitic infection called lymphatic filariasis. According to the World Health Organization, microscopic roundworms, primarily a species called Wuchereria bancrofti (responsible for 90% of cases), are transmitted through mosquito bites and nest directly inside lymphatic vessels. The adult worms disrupt normal lymphatic function, and chronic infection leads to severe tissue swelling and skin thickening known as elephantiasis. This is overwhelmingly a tropical disease, affecting communities in parts of Africa, Southeast Asia, and the Pacific Islands.
In all parts of the world, bacterial skin infections like cellulitis create a damaging cycle with lymphedema. Stagnant lymph fluid impairs the local immune response, making it easier for bacteria to take hold. At the same time, even a single serious skin infection can inhibit lymphatic vessel contraction and flow long after the infection clears. Research in the British Journal of Dermatology describes this as a “vicious cycle”: swelling invites infection, and infection worsens the swelling by further damaging the lymphatic vessels.
Genetic and Inherited Causes
Primary lymphedema results from a lymphatic system that didn’t develop normally. It’s far less common than secondary lymphedema but accounts for most cases in children and young adults.
Milroy disease is one well-known form that’s present at birth, caused by mutations in a gene involved in lymphatic vessel growth. Swelling typically appears in the feet and lower legs from infancy. Meige disease, a more common hereditary form, usually shows up around puberty or early adulthood. It follows an autosomal dominant inheritance pattern, meaning a child needs only one copy of the altered gene from one parent to develop it. Despite running clearly in families, researchers have not yet pinpointed the exact genetic change responsible for Meige disease.
Some people carry a genetic predisposition that doesn’t produce visible swelling until a triggering event, like surgery, pregnancy, or injury, pushes the system past its already-reduced capacity.
How Leg Lymphedema Progresses
The International Society of Lymphology classifies lymphedema into four stages, and understanding where you fall helps determine what to expect. Stage 0 is a latent phase: your lymphatic transport is already impaired, but there’s no visible swelling yet. This silent stage can last months or years. In Stage I, fluid begins to accumulate, and you’ll notice swelling that goes down when you elevate your leg. The tissue feels soft and pits when you press it.
Stage II marks a turning point. Elevating your leg no longer relieves the swelling, and the tissue starts to feel firmer as fat deposits and scar-like tissue (fibrosis) develop. By Stage III, the skin itself changes. It may become thick, rough, or develop warty growths, and the limb can become very large. At this point, the tissue often no longer pits when pressed because it has been replaced by fat and fibrous material rather than fluid alone.
Spotting It Early
One simple physical check is the Stemmer sign. Try to pinch and lift the skin on the top of your foot at the base of the second toe. If the skin feels thick and you can’t pinch it into a fold, that’s a positive Stemmer sign. A study comparing this test against lymphatic imaging found it was 88% sensitive, meaning it correctly identified lymphedema in most people who had it. However, a negative result doesn’t rule it out: specificity was only 59%, so some people with early-stage disease will still have normal-feeling skin.
Other early signs include a feeling of heaviness or tightness in one leg, shoes or socks fitting more snugly on one side, or skin that looks slightly puffier than the other leg at the end of the day. Catching it at Stage 0 or Stage I, before the tissue hardens, gives you the best chance of keeping it manageable with compression and movement-based therapies.