What Causes Swollen Legs and When Should I Worry?

Leg swelling can be scary. One leg swollen can be a sign of deep vein thrombosis, a potentially life-threatening condition caused by a blood clot. But there are dozens of other possible reasons for swollen legs—everything from sitting too long in economy class to serious heart or kidney problems. 

If your legs, ankles or feet have started to look like sausages, learn some of the main causes of leg swelling and when to see a doctor. A vein doctor can provide an accurate diagnosis and offer treatments for vein-related leg swelling. 

Common causes of leg swelling

The list of potential causes of swollen legs and ankles is a mile long and includes mild to severe medical issues, so getting an accurate diagnosis is critical. Here are some of them.

Blood clots

Swelling in one leg only, especially swelling in the calf, is a sign of DVT. You may also have pain, tenderness and warm, red skin. A clot deep in the leg is not necessarily dangerous by itself, but if the clot breaks off and travels to the lungs, it’s a potentially fatal medical emergency. Call 911 or go to the ER immediately if you have symptoms of a clot in the lung (pulmonary embolism). They include chest pain, shortness of breath and a fast or irregular heartbeat.

A blood clot that blocks a vein closer to the surface of the skin is called thrombophlebitis and can also make the leg swell. Like DVT, thrombophlebitis can cause skin redness, tenderness and warmth as well as pain in the affected area.

Chronic venous insufficiency

Persistently swollen legs and ankles may suggest chronic venous insufficiency (CVI), a common, long-term condition that occurs when the one-way valves in deep veins weaken. Normally, the valves propel blood from the legs back to the heart, but when they’re weak, blood flows backward and pools in the leg veins. 

Other signs of CVI include:

• Tired and achy legs
• Pain when walking
• Leg cramps (especially at night) and spasms
• Restless legs
• Leg skin that is flaky or itchy or has reddish patches
• Varicose veins

CVI can worsen quickly if not treated and eventually lead to open sores called leg ulcers.

Leg lymphedema

If you have CVI, you’re at risk of developing leg lymphedema—a double whammy, since that condition also causes leg swelling. 

The lymphatic system, which is part of the immune system, moves excess fluid out of the legs. But poor circulation, either from advanced CVI or a blot clot, can damage it. The result can be swelling in the lower legs and feet, heavy or achy legs, ulcers and skin changes including burning or itching, puffiness and redness. If one leg is bigger than the other, you could have leg lymphedema.

Standing or sitting for long periods

If you take long-distance flights, you stand all day at work or you’re mostly chair bound, your legs may pay the price thanks to fluid accumulation, which leads to leg swelling. Taking regular breaks to walk around and stretch, if possible, can help. So can doing ankle pump exercises and wearing compression socks or stockings.

Compression hose should be worn when flying and during car rides that are more than two hours long to help prevent DVT and make your legs feel better.

Being sedentary or obese

Obesity and lack of exercise can also cause fluid buildup in the legs that leads to leg swelling.

Injury

Injury to a bone, tendon or ligament in the leg can trigger inflammation and swelling. It typically goes away once the injury heals. 

Certain medicines

Some medications can cause swollen legs, such as:

• Some nonsteroidal anti-inflammatory drugs (ibuprofen, aspirin, naproxen)
• Hormone medications that contain estrogen or progesterone
• Certain antidepressants
• High blood pressure medicines called calcium channel blockers (amlodipine, nifedipine)

If you take any of these drugs and develop swollen legs, tell your doctor.

Serious medical conditions

Some chronic health conditions can cause fluid buildup, leading to swelling in the legs, feet and elsewhere. These conditions include:

• Kidney problems (chronic kidney disease, kidney failure)
• Heart problems (pericarditis, cardiomyopathy, congestive heart failure)
• Cellulitis, a serious bacterial infection that’s most common in the lower leg and may cause leg swelling, pain, fever and a red area of skin that gets larger
• Preeclampsia, a pregnancy complication that causes swelling in the legs, face and hands

When should I be concerned about leg swelling?

Unless the swelling resolves quickly, it’s a good idea to see a doctor to get a diagnosis and rule out a serious medical issue that could become worse if left untreated. Call a doctor right away if you have trouble breathing or significant unexplained leg pain.

Swollen legs treatments

If you suspect a vein condition might be the answer to “Why are my legs swollen?”, make an appointment with a vein doctor. Vein doctors can treat blood clots and chronic venous insufficiency, which can reduce swelling and other symptoms often seen with swollen legs, such as pain and tenderness.

Treatment options include:

Compression socks or stockings

These tight-fitting garments prevent blood from pooling in the legs, helping to relieve leg swelling caused by CVI, varicose veins and sitting or standing for long periods. For some people, they may be the only treatment needed to reduce uncomfortable leg swelling.

Medication

If you have DVT, you may be prescribed anticoagulants (blood thinners) to break up the clot. Or your doctor may recommend a fast-acting, clot-busting medication called a thrombolytic, which can be delivered intravenously or injected into the clot.

Vein procedures

Your doctor can close problematic veins with minimally invasive surgery. This can be done using radio waves (radiofrequency ablation) or light (endovenous laser treatment) or by injecting the vein with a chemical that causes it to collapse (sclerotherapy). The vein can also be sealed shut with a glue-like substance called VenaSeal.

Surgery

Surgical procedures for DVT include widening the affected vein to improve blood flow (angioplasty) and placement of a vena cava filter, which prevents broken-off clots from causing a pulmonary embolism.

Rarely, DVT patients need to have a blood clot removed surgically. This surgery can be performed by a vascular surgeon.

Ready to get help for heavy legs? Make an appointment with one of our vein specialists today. 

Medically reviewed by Douglas Ward, MD 

Written by Jessica Brown, a health and science writer/editor based in Nanuet, New York. She has written for Water’s Edge Dermatology, Prevention magazine, jnj.com, BCRF.org, and many other outlets.