Answers

Why is one leg more swollen than the other?

One swollen leg is a reason to be seen promptly: a clot (DVT) or skin infection are the common causes. Lymphedema is one-sided too but needs diagnosing first.

By The Renu lymphatic and massage team · 6 min read

Swelling in one leg, rather than both, points to a local problem in that leg rather than a whole-body cause, and the two most common are a blood clot in a deep vein and a skin infection. Both need a doctor the same day: the NHS asks for urgent care for one swollen leg with no known cause, and the Cleveland Clinic lists swelling that affects only one limb among the signs to call a provider about. Lymphedema is also usually one-sided, and once a clot and infection have been ruled out, manual lymphatic drainage becomes appropriate. We do not treat an unexplained single swollen leg until it has been checked.

Most of the swelling questions we hear at the clinic are about two legs: both ankles after a flight, both feet in the heat, both shins at the end of a shift. One leg is a different question, and we want to answer it carefully, because the honest answer is that a massage booking is not the first step.

Why one side matters more than two

When both legs swell, the cause is usually something acting on the whole body: gravity after a long day, heat, pregnancy, salt, a medication, or the heart, liver or kidneys. When only one leg swells, something is happening in that leg. The Merck Manual puts it directly: the most common causes of swelling in a single limb are a blood clot in a deep vein (deep vein thrombosis) and a skin infection (cellulitis), with blockage of lymphatic vessels as a less frequent cause.

That is why the guidance is consistent. The NHS asks you to get an urgent GP appointment or call its 111 service if you have swelling in one ankle, foot or leg and do not know the cause. The Cleveland Clinic lists “swelling that affects only one limb (especially a leg)” among the reasons to call a provider. The Merck Manual counts swelling in only one leg, together with sudden onset, significant pain or tenderness, shortness of breath and coughing up blood, as a warning sign that calls for prompt medical attention.

The signs of a clot

A deep vein thrombosis is the diagnosis everyone is trying to exclude first, because a piece of the clot can travel to the lungs. The NHS lists the symptoms in the leg as:

throbbing pain in one leg (rarely both), usually in the calf or thigh;
swelling in one leg (rarely both);
red, blue or darkened skin around the painful area, which can be harder to see on brown or black skin;
swollen veins.

The NHS adds that these symptoms can occur in an arm if the clot is there, and that a clot is more likely after a journey of more than four hours, during or after surgery, after three or more days in bed, in pregnancy and the six weeks after birth, and when dehydrated. Being over 60, overweight, a smoker, having varicose veins, cancer or heart failure, taking oestrogen-containing contraception or hormone therapy, and a previous clot all raise the baseline risk.

Diagnosis is straightforward when it is sought. The NHS says a doctor who suspects DVT should refer you to hospital within 24 hours for an ultrasound scan that shows whether blood is flowing normally through the vein. Treatment is blood-thinning medicine, usually for at least three months.

The signs of an infection

Cellulitis is the other common cause, and it looks different: the National Cancer Institute describes pain, tenderness, redness and swelling in the affected area, skin that feels warm to the touch, and fever. The NHS asks for urgent care if a swollen area is red or feels hot, or if you have a very high temperature or feel hot, cold and shivery. Cellulitis is treated with antibiotics, and the NCI warns that left untreated it can become life-threatening. A limb with existing lymphedema is especially prone to it, which is one more reason the swollen leg needs eyes on it quickly.

When one swollen leg is lymphatic

Once a clot and an infection are off the table, a one-sided leg often turns out to be lymphedema, and lymphedema is, by its nature, usually asymmetrical. The NCI lists “swelling in an arm or leg that makes it appear larger than the other arm or leg” among its signs, and the Cleveland Clinic includes “your arms or legs appear to be slightly different sizes” in its symptom list. The Canadian Cancer Society describes lymphedema developing in the leg after treatment for lymphoma, melanoma and uterine, prostate, vulvar and ovarian cancers, because the lymph nodes in the pelvis and groin are removed or irradiated on one side or both.

Lymphedema does not need cancer, though. Macmillan notes that not everyone with lymphoedema has had cancer, and the Cleveland Clinic lists surgery, trauma, infection, lack of activity, obesity and chronic blood vessel problems among the causes, so a leg that has had a knee replacement, a bad fracture or years of vein trouble can swell on that side alone.

Two features help a clinician tell the difference, although none replaces the scan. Macmillan notes that in lymphoedema your clothing, shoes or jewellery may feel tighter before you see swelling, and that the limb may feel heavy, tight, full or stiff; the NCI notes that early lymphedema leaves a dent when pressed, while long-standing lymphedema no longer does. Macmillan is equally clear that swelling, aching and redness in a limb can also be a blood clot and must be reported to a doctor or nurse straight away.

The Cleveland Clinic describes how providers sort this out: a Doppler ultrasound to look at blood flow and rule out clots, and sometimes MRI or CT to check whether something is pressing on the lymphatic system. Our Learning Centre page on lymphedema and lipedema explains what happens after the diagnosis.

What we do at Renu, and in what order

We ask. Before a first lymphatic appointment we want to know when the swelling started, whether it is one-sided, whether it hurts, whether the skin is warm or discoloured, and whether a doctor has seen it. If the answer to the last question is no and the leg is new and unexplained, we will ask you to be seen first, because the Cleveland Clinic lists deep vein thrombosis, blood clots, cellulitis, infection and fever among the conditions in which lymphatic massage should be avoided, and because massaging a leg with a clot in it is a risk we are not willing to take on your behalf. If you have had a clot in the past and are now on treatment, our answer on lymphatic drainage after a blood clot covers how that changes things.

Once the leg has been cleared, the right booking depends on the diagnosis. Swelling after an injury or operation on that side usually suits a classic lymphatic drainage massage. Diagnosed lymphedema suits complete decongestive therapy with Meeghan Mackenzie, our Certified Lymphedema Therapist and Certified Compression Fitter, where drainage, compression, skin care and exercise are planned together. If you are unsure which applies, contact us and describe the leg; we will tell you plainly whether it sounds like something for us or for a doctor first.

When to see a doctor, and how fast

Same day, by urgent appointment or a nurse line, if you have:

swelling in one leg with no obvious cause;
throbbing or cramping pain in one calf or thigh;
warmth, redness or darkening of the skin over the swollen area;
veins that look swollen or feel hard and sore;
a high temperature or feeling hot, cold and shivery with the swelling.

Emergency services if one-leg swelling comes with shortness of breath, chest pain or tightness, coughing up blood, palpitations, or feeling faint, confused or clammy, because the clot may have reached the lungs. The Learning Centre’s when to seek medical care page lists the same red flags for every kind of swelling we see.

Questions people ask

My left calf is bigger than my right but it does not hurt. Is that still urgent?

Yes, have it checked. The NHS asks for an urgent GP appointment or a call to its 111 service when one ankle, foot or leg is swollen and you do not know the cause, and it does not make pain a condition. The CDC notes that about half of people with a deep vein thrombosis have no symptoms at all, so a painless size difference is not reassurance on its own.

How do doctors find out whether it is a clot?

With an ultrasound scan of the leg veins. The NHS says that if a doctor suspects DVT you should be referred to hospital within 24 hours for an ultrasound that shows whether blood is flowing normally through the vein. The Cleveland Clinic lists a Doppler ultrasound as the test that can find obstructions and rule out blood clots before lymphedema is considered.

Could one swollen leg be lymphedema rather than a clot?

It could, and lymphedema is very often one-sided. The National Cancer Institute lists swelling in one arm or leg that makes it look larger than the other among its signs, and the Canadian Cancer Society describes lymphedema developing in the leg after treatment for cancers of the pelvis. Lymphedema is a diagnosis made after the dangerous causes have been excluded, not instead of excluding them.

Can I come to Renu first and let you decide?

We will always talk to you, but we are not the right first stop for a new, unexplained single swollen leg. The Cleveland Clinic lists deep vein thrombosis, blood clots, cellulitis and infection among the conditions in which lymphatic massage should be avoided. Once a doctor has ruled those out, we are glad to help, and we will ask what they found.