What are the Main Causes of Swelling in a Single Leg?

Written By Center for Vein Restoration
Causes of swelling in a single leg

Have you noticed that one of your legs is swollen but not the other? People wonder when to be concerned about lower extremity leg swelling (edema). Many vein diseases provoke swelling, so it is difficult to diagnose without the help of a medical professional. Some of these problems are mild; others are medical emergencies. Continue reading to learn more about vein disease and when to seek professional attention.

Understanding Blood Flow and Fluid Accumulation in the Legs

Blood circulation is similar to the dam infrastructure of rivers, like the Mighty Mississippi. Using locks, levees, and dams, cargo ships move upriver to deliver valuable resources to northern regions.

Veins use a similar infrastructure. Vein valves open in one direction, allowing blood to move upstream, removing waste and toxins and refueling the blood with oxygen.

If storms come or the dams break, riverbanks erode and flood the overwhelmed areas. The same is true for veins. If valves malfunction, circulation slows or ceases, causing fluid, waste, and blood accumulation in the lower extremities.

Swelling in One Leg vs. Both Legs

Blood accumulation in the feet, ankles, or legs causes swelling, also known as edema. Swelling can occur in one or both legs. Either way, edema indicates blood flow issues.

However, single-leg edema often suggests a critical problem. Rapid or severe swelling is a medical emergency and may indicate deep vein thrombosis (DVT), a potentially life-threatening blood clot.

Swelling in both legs typically signifies an ongoing, chronic disorder. Regardless of whether one or both legs are impacted by blood pooling, early treatment is essential to relieve symptoms and prevent complications.

What Causes Swelling in One Leg?

Swelling in one leg has several different causes. Plaque build-up within the blood vessels restricts blood movement. Overwhelmed and dilated veins stretch and become susceptible to blood pooling. Vein valves malfunction and prevent deoxygenated blood from efficiently moving upstream.

When blood pools, downstream blood movement causes reflux, further complicating the situation. Compromised vein walls, malfunctioning valves, and encumbered vessels can cause swelling in one leg. However, treating the cause of single-leg swelling promotes adequate blood flow and circulation.

Deep Vein Thrombosis (DVT)

Blood clots that form in non-superficial, deep veins are called deep vein thrombosis. This critical condition usually occurs in large leg veins. Signs that you may be experiencing a DVT are the following:

  • Leg swelling
  • Pain, cramping, or soreness that usually begins in the calf muscle
  • Skin color changes, generally red or purple
  • A warm feeling on the affected leg

Various medical conditions, recent surgery, vein disease, and inactivity are some of the risk factors for developing DVTs.

Immediate treatment is vital because blood clots often break loose from the vein wall and travel to the lungs. When clots become lodged in the lungs, they block the blood supply, causing pulmonary embolism.

If you notice any of the above symptoms, seek medical attention immediately to prevent further complications.

Peripheral Artery Disease (PAD)

Like a beaver's dam restricts water flow, plaque build-up inhibits blood flow. Arteries narrow and harden due to the build-up of fat in the artery wall. In the medical world, this condition is known as arteriosclerosis, but most refer to this condition as a "clogged artery."

These restricted arteries cause inadequate oxygen supply to tissues and organs. When the oxygen supply is insufficient, PAD results. Though the prevalence of PAD is more significant in men, 12 percent of Americans suffer from this disease.

Surprisingly, 20 percent of people with PAD show no symptoms, causing it to be underrecognized. Mild cases of peripheral arterial disease are either asymptomatic or show intermittent symptoms.

These symptoms often worsen during activity and resolve during rest. This characteristic indicates PAD and is called intermittent claudication. Signs of PAD are the following:

  1. Painful cramps in lower extremities
  2. Fatigued or "heavy" legs
  3. Coolness in the feet and ankles
  4. Changes in skin color
  5. Loss of leg hairs
  6. Shiny skin on legs

Single-leg swelling related to PAD generally happens when the leg has been immobilized or is in a dependent position for pain relief.

If untreated, the oxygen supply will continue to be insufficient. Unfortunately, ulcers and gangrene can result. Often people who receive treatment from a vein specialist prevent complications and have a favorable prognosis.


Lymphedema is a chronic swelling caused by damage to the lymphatic system. Less than five percent of all lymphedema diagnoses have genetic roots. More than 95 percent of cases result from obstruction or disruption of the lymphatic vessels. The most common reasons are the following:

  • Surgery
  • Radiation
  • Trauma
  • Tumor
  • Lymphatic filariasis

Chronic venous insufficiency (CVI) sufferers often experience leakage of lymph, a clear-to-white fluid made of white blood cells, causing swelling and lymphedema. Achy, painfully tight legs are some symptoms of this condition.

One telltale symptom is pitting edema, which becomes apparent when the swollen tissue remains indented after you remove the pressure. For example, if you press on your swollen feet and the dent from your finger remains for even a second, you are experiencing pitting edema.

A physical exam, CT scan, and MRI can identify lymphatic obstruction. Though curing lymphedema is challenging, a board-certified vein specialist can provide treatments to slow the disease process and prevent further complications.

Venous Insufficiency

Venous insufficiency, or vein disease, develops from impaired vein function, resulting in swelling, discomfort, and skin changes in one or both legs. Obstruction of veins, decreased muscle contractions, and ineffective valves cause this disease.

Elevated vein pressure, or venous hypertension, occurs when veins struggle to force blood upriver—the increased vascular pressure results in swelling in the legs and further damage to the veins and valves. Prolonged venous insufficiency causes significant edema, inflammation, and low oxygen supply. People with the following risk factors are more prone to develop this vein disease:

  1. History of DVT or physical trauma
  2. Age
  3. Overweight
  4. Sitting or standing for prolonged periods
  5. Pregnancy

If you think you are suffering from venous insufficiency, a vein specialist can perform a physical evaluation and ultrasound to determine the function and flow in the veins. Several treatment modalities are available:

Early treatment reduces complication risks and improves outcomes, so don’t wait.

Varicose Veins

Varicose veins are enlarged, dilated veins that twist and turn. They are commonly found in the legs. Though not always symptomatic, some common signs are painful, tired, and "heavy" legs.

Similar to venous insufficiency, varicose veins result from impaired venous return. Malfunctioning vein valves cause pooling and reflux. Vein walls then become stretched and weak. The overwhelmed veins bend and curve under the increased pressure.

Initially, veins may be firm to the touch but not visible. As the disease progresses, varicose veins protrude, distort, and become observable. After an exam and ultrasound, a specialized physician will prescribe the right treatment plan for you. The treatment options for varicose veins are the same as those for venous insufficiency.

Understanding the Complications of Untreated Leg Swelling

Treatment for leg swelling is essential, whether you experience the symptoms in one or both legs. Remember, varicose veins, leg fatigue, and pain in the calf are not normal. Instead, these symptoms are warning signs of impending complications.

Many people dismiss leg problems as part of aging or assume it is only a cosmetic issue. This misinformation is the cause of severe complications. Leg swelling in one leg often indicates a critical condition. If left untreated, vascular stress can result in the following complications:

If you are concerned about your venous health, don't wait. Treatment will help support the veins, eliminate ineffective veins, and promote circulation.

When to Consult a Vein Specialist for Leg Swelling

It’s never too early to talk to a vein specialist. Whether you are tired of bothersome varicose veins or concerned about venous health, a board-certified vein center provides expert guidance.

If you experience the previously mentioned symptoms, early treatment from a knowledgeable physician provides you with the tools to fight vein disease.

Treatment modalities range from lifestyle changes to minimally invasive, in-office procedures. Remember, if you are experiencing pain in the calf, a hard and tender vein, or a bleeding varicose vein, call 911.

Tips to Prevent Leg Swelling

Treatment of leg swelling should address the underlying problems. If you suffer from symptoms related to weak vein walls, malfunctioning valves, or plaque build-up, treatment options — like laser ablation, sclerotherapy, or compression stockings — are available.

However, prevention is the best treatment plan. Some tips that will help you prevent leg swelling are listed below:

  • Get the blood pumping
  • Avoid sitting and standing for extended periods
  • Use compression stockings
  • Maintain a healthy weight
  • Eat high-fiber foods

Conclusion: The Causes of Leg Swelling and the Importance of Treatment

Leg swelling is a symptom worth addressing because it indicates an underlying issue. Single-leg edema could indicate a severe and life-threatening emergency. If treated early, you could prevent complications and experience relief.

At Center for Vein Restoration (CVI), we are committed to providing clean, safe, and affordable vein care. Ask us about our complimentary provider visits. For more information, give us a call or schedule an appointment online. Our vein clinic has multiple locations in the US.

Find CVR Near You