When Is Leg Swelling a Sign of Something Serious?

Your legs are looking like they belong on the Stay Puft Marshmallow Man. What could be going on?

Good question — but not an easy one to answer. “A hundred different things can cause swollen legs,” says vascular surgeon Francis Caputo, MD. And those things can range from no big deal to very serious.

When should you be concerned? We talked to Dr. Caputo for the rundown on some common causes of leg swelling — and if they need a foot rest or a doctor’s visit.  

When leg swelling is mild

If you’ve been on your feet all day, it’s not uncommon to have some puffiness in your feet or legs. Same if you’ve been sitting for hours in the car or on a plane. That swelling, called edema, strikes when fluid builds up in the feet and legs. It’s more common in people who are overweight or pregnant but can happen to anyone.

To avoid swelling, limit salt in your diet. When you’re traveling, get up frequently to stretch and move. If you have mild swelling and want to de-puff, go for a walk, do some ankle rolls or prop your feet up on pillows.

Deep vein thrombosis

Deep-vein thrombosis (DVT) is a blood clot that forms in a vein of the body, usually (but not always) in the pelvis, thigh or lower leg. Typical symptoms of DVT include:

• Swelling in one leg, sometimes accompanied by skin that is red or warm to the touch.
• Pain or tenderness in the leg.
• Enlarged veins near the skin’s surface.

People with a condition called May-Thurner syndrome (MTS) are at higher risk of DVT. An artery in the leg presses on a nearby vein, making clots more likely in the left leg.

If a clot breaks free, it can travel to the lungs and block the flow of blood, leading to a pulmonary embolism — a very serious situation. Signs of a pulmonary embolism show up in your chest rather than your legs:

• Sudden shortness of breath.
• Pain in the chest or back.
• Cough.
• Dizziness.
• Rapid heartbeat.

If you experience signs of DVT or pulmonary embolism, putting your feet up isn’t enough. It’s important to seek treatment right away.

Venous insufficiency

Sometimes, the veins in the legs can become weakened. When that happens, blood doesn’t flow as easily back to the heart. As a result, you can develop varicose veins and fluid buildup in the legs. Venous insufficiency sometimes develops in people who have had DVT in the past. 

Lymphedema

Lymphedema occurs when the body’s lymph nodes aren’t filtering lymph fluid as well as they should. When that happens, it can cause swelling of one or more limbs, ranging from mild to dramatic.

Lymphedema sometimes occurs in people who have had lymph nodes removed for cancer treatment. But it can affect others whose lymph nodes are damaged or working improperly for other reasons.

Heart, kidney and liver disease

When organs aren’t working as well as they should, fluid can build up in the legs. Congestive heart failure, kidney disease and liver disease can all cause edema.

If you have any of these conditions and notice new or persistent swelling in your legs, mention it to your doctor. 

When to seek treatment for leg swelling

Plenty of other conditions can also make legs swell, including infections, injuries and diseases such as arthritis. If the puffiness isn’t too dramatic and resolves within a day or so, it’s probably nothing to lose sleep over. But if it happens more often, lasts longer, affects just one leg or teams up with other symptoms, it’s a wise idea to let a healthcare provider weigh in.

“Swollen legs are often a sign of a bigger problem,” says Dr. Caputo. “If you have leg swelling, you should get checked out by your primary care doctor to figure out what’s going on.”