You pull your socks off at night, and one ankle has a deep ring pressed into it. The other one doesn't. Maybe the calf on that side looks a little fuller too. Swelling in one leg is one of those things people tend to shrug off. I'd rather you didn't. When only one leg swells, the cause is usually sitting in that leg, and one possible cause is a blood clot.
Key Takeaways
- Swelling in one leg points to a problem in that leg, while swelling in both legs more often comes from a whole-body cause.
- A blood clot (DVT) is the cause to rule out first, especially if the swelling came on quickly or the calf hurts.
- Leaking leg veins, an old clot, an injury, a skin infection and lymphedema can also swell one leg.
- Chest pain or shortness of breath with a swollen leg is a 911 call.
- A painless duplex ultrasound in the office is usually the fastest way to find the cause.
Why Swelling in One Leg Is Different
Most leg swelling that shows up in both legs comes from something that affects your whole body: heat, long hours on your feet, certain medications, or heart, kidney, or liver problems. When just one leg swells, we begin by examining that leg. The veins, the skin, the lymph channels, and the muscles of that one leg become the suspects.
Additionally, I suggest seeing a doctor if only one leg is swollen. A new, one-sided swelling deserves a look within a day or so, and sooner if it hurts.
Common Causes of Swelling in One Leg
A Blood Clot (Deep Vein Thrombosis)
A clot in a deep vein of the calf or thigh blocks blood from leaving the leg, so fluid backs up into the tissue. The leg may ache, feel tight, look red or bluish, or feel warm. Some clots cause almost nothing besides swelling. Recent surgery, a hospital stay, a long drive or flight, pregnancy, hormone medicines, and cancer all raise the risk. Read the signs of DVT and the causes of DVT if any of that sounds familiar.
Leaking Veins (Venous Insufficiency)
The valves inside your leg veins can wear out, and they don't always wear out evenly. One leg can have much more backward flow than the other. That leg swells more by evening, feels heavier and may have bulging veins. This is chronic venous insufficiency, and it's the most common long-term cause I treat. Visible varicose veins on one side are a strong clue; here's more on varicose vein symptoms.
Damage From an Old Clot
After a DVT, the vein can heal with scarred valves. Months or years later, that leg may still swell, ache, and change color. Doctors call this post-thrombotic syndrome. If you've had a clot before, my article on living with DVT covers what to watch for.
Injury, a Strained Muscle or a Baker's Cyst
Swelling in a leg can be caused by a sprained ankle, a pulled calf muscle, or a fall. A Baker's cyst, a fluid-filled pocket behind the knee, can also cause leg swelling. If one bursts, it can cause calf pain and swelling that looks a lot like a clot. The only way to tell them apart is with imaging.
A Skin Infection (Cellulitis)
Cellulitis typically presents as a red, hot, tender, and swollen leg (and sometimes with fever). It's frequently preceded by a small cut, a bug bite, or cracked skin between the toes. It requires antibiotics so don't wait. Here's how I'd think about a leg that feels warm to the touch.
Lymphedema
If lymph nodes in the groin or pelvis were removed or treated with radiation, or the lymph channels were damaged, fluid can collect in that leg. Lymphedema tends to be firm and doesn't go down much overnight. It's managed by trained lymphedema therapists, and I can help sort out whether that's what you're dealing with.
Pressure on the Vein Higher Up
Sometimes the problem isn't in the leg at all. A vein in the pelvis can be squeezed by an artery crossing over it or, less often, by a mass. That pressure slows blood leaving the leg. It's one reason I sometimes look above the leg when the leg itself checks out normal.
Left Leg Swelling vs. Right Leg Swelling
People often ask me whether the side matters. Usually it doesn't. The causes above can show up in either leg. The one difference: the main vein draining the left leg crosses under an artery in the pelvis, where it can get compressed. That's one reason left-sided clots and left leg swelling come up a little more often. Either way, the workup is the same.
When Swelling in One Leg Is an Emergency
Call 911 or go to the nearest emergency room if swelling in one leg comes with:
- Chest pain, shortness of breath, coughing up blood or a racing heartbeat. A clot may have traveled to the lungs.
- A leg that is suddenly cold, pale or very painful.
- Fever with a red, hot, spreading area on the leg.
Get seen the same day, by us, your doctor or urgent care, if the swelling came on over hours to a few days, the calf hurts or is tender, or the leg is warm or discolored. For slower, milder changes, here's my guide on when to worry about leg swelling.
How I Find the Cause
When I see a patient, I start with questions. Questions like: When did it start? Did something trigger this, like surgery, a trip, or an injury? Does it go down overnight? Then we will begin an examination. We will start by checking your blood pressure, skin pulses, and whether any areas are tender.
Next comes a duplex ultrasound. It's painless, uses no radiation, and shows the blood flow inside your veins. It can find a clot and show leaking valves in the same exam. If I'm also concerned about the arteries, an ankle-brachial index test checks circulation in a few minutes. The National Library of Medicine has a helpful overview of leg and ankle swelling, too.
Treatment Depends on the Cause
- Blood clot: blood thinners, with close follow-up. Later on, compression may help with lingering swelling. The National Heart, Lung, and Blood Institute explains how clots are treated.
- Leaking veins: compression stockings, walking and leg elevation first. When a leaking vein is the source, radiofrequency ablation closes it from the inside, and sclerotherapy treats smaller veins.
- Infection: antibiotics, usually through your primary care doctor or urgent care.
- Lymphedema: a referral to lymphedema therapy for specialized wraps, garments and massage.
- Injury or cyst: rest, ice and follow-up with your doctor or an orthopedic provider.
What Not to Do While You Wait
If you have a swollen, sore calf, I would advise you not to put it in a compression stocking until a blood clot has been ruled out. Keep your leg raised when you sit and stay hydrated. Visit a medical professional as soon as you can to get it checked. If it's been swollen for weeks without pain, it's less urgent, but it still deserves an answer.
Frequently Asked Questions
Swelling in one leg usually means the cause is in that leg. Common reasons are a blood clot, leaking veins, an old clot that damaged the vein, an injury, a skin infection, or lymphedema. An exam and duplex ultrasound sort these out.
Yes. Leaking veins and lymphedema often cause swelling in one leg without much pain, and some blood clots cause swelling with little or no pain. Painless swelling in one leg still needs to be checked.
Not usually. The same causes affect either leg. The left leg's main vein can be compressed in the pelvis, so left-sided swelling and clots come up a bit more often, but the evaluation is the same.
Go to the ER or call 911 if leg swelling comes with chest pain, shortness of breath, a cold or very painful leg, or fever with spreading redness. For sudden one-leg swelling with calf pain, get seen the same day.
A duplex ultrasound is the main test. It's painless, takes about half an hour and shows whether blood is flowing through the deep veins or blocked by a clot.
You See the Same Doctor Every Time
Coastal Vascular Center is a physician-owned practice, not a corporate chain. You see me at every visit, and I perform every procedure myself. There's no hand-off to a PA or nurse practitioner. We see patients in Pearland (8619 Broadway St, Suite 105) and Lake Jackson (201 Oak Dr South, Suite 105), and we accept most insurance plans.
Get Swelling in One Leg Checked
If one leg has started to swell, an ultrasound evaluation can find out why. You'll see Dr. Ayar at every visit in Pearland or Lake Jackson.
