Swollen ankles and feet happen when excess fluid collects in the tissues of your lower legs, pulled there by gravity and held there by one of several possible causes. The medical term is peripheral edema, and it ranges from harmless (standing too long on a hot day) to a signal that your heart, kidneys, or veins aren’t working properly. The pattern of your swelling, whether it affects one leg or both, and how quickly it appeared all point toward different explanations.
How Fluid Ends Up in Your Feet
Your blood vessels constantly exchange fluid with the surrounding tissue. Tiny capillaries push fluid out while simultaneously pulling it back in. When that balance tips, either because pressure inside the vessels rises or because the vessels become leakier, fluid accumulates faster than your body can drain it. Because your feet and ankles sit at the lowest point of your body, gravity keeps that extra fluid pooled there.
Salt plays a direct role. When you take in more sodium than your kidneys can flush, your body holds onto water to keep blood chemistry balanced. That extra water increases pressure inside blood vessels and pushes more fluid into surrounding tissue. Heart associations generally recommend staying under 2,000 mg of sodium per day if you already have fluid retention issues, though the average person consumes well above that.
The Most Common Causes
Venous Insufficiency
This is one of the most frequent reasons for chronic ankle swelling, especially in people over 50. Veins in your legs rely on one-way valves to push blood upward against gravity. When those valves weaken or fail, blood pools in the lower legs, raising pressure in the veins and forcing fluid into the tissue. Over time you may notice skin discoloration around the ankles, a brownish or reddish tint that darkens gradually. Varicose veins often accompany the swelling. Treatment typically starts with compression stockings and leg elevation, though procedures like vein ablation or sclerotherapy are options when conservative measures aren’t enough.
Heart Failure
When the heart can’t pump blood efficiently, it backs up in the veins. The legs, ankles, and feet swell because blood returning from the lower body essentially stalls. You might also notice swelling in the abdomen, shortness of breath (especially when lying flat), or unusual fatigue. Both ankles typically swell equally. Heart failure is the cause doctors are most concerned about ruling out when someone reports persistent bilateral swelling.
Kidney Disease
Your kidneys filter excess fluid and sodium from the blood. When they lose function, that fluid stays in circulation and eventually leaks into tissues. Kidney-related swelling often shows up in the feet and ankles but can also appear around the eyes and in the hands, particularly in the morning.
Liver Disease
Advanced liver disease, particularly cirrhosis, reduces production of a key blood protein that helps keep fluid inside your vessels. Without enough of that protein, fluid seeps out more easily. Liver-related swelling typically involves the abdomen as well as the legs.
Medications
Several common medications cause ankle swelling as a side effect. Blood pressure drugs called calcium channel blockers are among the most well-known culprits. They work by relaxing blood vessels, but that relaxation can increase pressure in the small capillaries of the legs, pushing fluid into surrounding tissue. Diabetes medications in the thiazolidinedione class cause fluid retention through a different mechanism, increasing both vessel permeability and sodium retention in the kidneys. Anti-inflammatory painkillers, certain steroids, and some hormone therapies can also contribute. If your swelling started shortly after beginning a new medication, that timing is worth noting.
One Leg vs. Both Legs Matters
When both ankles swell symmetrically, the cause is usually systemic: something affecting your whole body like heart function, kidney health, medication side effects, or high sodium intake. When only one leg swells, the explanation is more often local.
Sudden swelling in a single leg is the pattern that needs the most urgent attention. A blood clot in a deep vein, called deep vein thrombosis or DVT, blocks blood flow and causes rapid swelling, often with warmth, redness, or pain in the calf. This requires same-day medical evaluation because the clot can break loose and travel to the lungs.
When DVT is ruled out, single-leg swelling has other explanations. About 40% of cases turn out to be a muscle strain, tear, or twisting injury. Less common causes include infection in the skin (cellulitis, which shows redness and warmth), a fluid-filled cyst behind the knee, or lymphatic blockage from prior surgery or radiation in the groin area. Chronic one-sided swelling most often traces back to venous insufficiency in that particular leg.
Swelling During Pregnancy
Mild ankle swelling is normal during pregnancy, particularly in the third trimester. Your body retains significantly more fluid during pregnancy, and hormonal shifts make blood vessels more relaxed and permeable. On top of that, the growing uterus physically compresses the large vein (the inferior vena cava) that returns blood from your lower body to your heart, slowing circulation in the legs.
Sleeping on your left side helps because it takes pressure off that vein. Staying active, wearing supportive shoes, and elevating your feet when resting all reduce swelling. Sudden or severe swelling, especially if paired with headaches or vision changes, is a different situation and can signal a pregnancy complication called preeclampsia.
How to Check the Severity
Doctors assess swelling by pressing a finger into the swollen area for a few seconds and watching what happens when they release. If the pressure leaves a visible dent that takes time to bounce back, that’s called pitting edema, and it’s graded on a 1 to 4 scale:
- Grade 1: A shallow 2 mm dent that rebounds immediately.
- Grade 2: A 3 to 4 mm dent that fills back in within 15 seconds.
- Grade 3: A 5 to 6 mm dent that takes up to 60 seconds to rebound.
- Grade 4: An 8 mm dent that can take two to three minutes to fill back in.
You can do this simple press test at home. If your dent falls in the Grade 3 or 4 range, that level of fluid retention warrants medical evaluation. Even lower-grade pitting that persists for more than a few days is worth bringing up with a doctor, especially if it’s new.
Practical Ways to Reduce Swelling
Elevation is the simplest and most effective immediate relief. Prop your feet up so they’re at or above the level of your heart when you’re resting. Research on post-surgical patients found that even low elevation, roughly the height of a pillow (about 10 cm), produced meaningful swelling reduction, and that higher elevation didn’t necessarily work better while being less comfortable. So simply resting with your feet up on a cushion or pillow for 20 minutes or more can make a noticeable difference.
Compression socks or stockings work by squeezing the veins in your lower legs, helping push blood back toward the heart. They’re particularly effective for venous insufficiency and for people who stand or sit for long periods. Graduated compression stockings, which are tighter at the ankle and looser up the calf, are the most helpful type. Put them on in the morning before swelling sets in for the day.
Reducing sodium intake is one of the most impactful dietary changes. Processed foods, restaurant meals, and canned soups are common sources of hidden sodium. For people with heart failure or significant fluid retention, guidelines recommend keeping sodium under 2,000 mg per day. For context, a single teaspoon of table salt contains about 2,300 mg.
Movement matters, too. Walking activates the calf muscles, which act as a pump to push venous blood upward. If your job keeps you seated for hours, flexing your ankles up and down periodically mimics some of that pumping action. Avoiding prolonged standing in one position helps for the same reason: your calf muscles aren’t contracting, and blood pools in the lower legs.
When Swelling Signals Something Serious
Most ankle swelling is benign and related to lifestyle factors like prolonged sitting, heat, salty meals, or being on your feet all day. But certain patterns deserve prompt attention. Swelling in one leg that comes on suddenly, particularly with calf pain or redness, raises concern for a blood clot. Swelling in both legs paired with shortness of breath could point to heart failure or a clot that has already traveled to the lungs. Swelling that leaves deep, slow-to-rebound pits, gets worse over days, or is accompanied by reduced urine output suggests your kidneys or heart may be struggling to manage fluid balance.
If your swelling is mild, symmetrical, worse at the end of the day, and improves overnight or with elevation, it’s more likely related to gravity, diet, or venous insufficiency. Tracking what makes it better or worse, whether it’s new or longstanding, and whether it comes with other symptoms gives your doctor useful information for narrowing down the cause quickly.