Swelling in just one ankle, rather than both, narrows the list of likely causes considerably. When only your right ankle swells, the problem is almost always local to that leg: an injury, a blood clot, a vein that isn’t working properly, or an infection. Conditions that cause both ankles to swell, like heart or kidney problems, rarely show up on one side alone.
Why One Ankle Matters More Than Two
Bilateral swelling (both ankles) typically points to a systemic issue: fluid retention from heart, kidney, or liver problems, or simply the effect of hot weather causing small blood vessels to dilate and leak extra fluid into surrounding tissues. One-sided swelling tells a different story. It signals something happening in that specific leg, whether it’s damage to a vein, a joint problem, a recent injury you may not even remember, or a clot forming in a deep vein.
This distinction is the first thing a clinician will note, and it should guide your own thinking too. If your right ankle swells but your left looks normal, the explanations below are the most common reasons.
Chronic Venous Insufficiency
The most common reason for persistent swelling in one ankle is a problem with the valves inside your leg veins. Your veins contain small one-way valves that push blood upward toward your heart against gravity. When a valve becomes damaged, it can’t close properly, and blood flows backward and pools in your lower leg. This is called chronic venous insufficiency, or CVI.
The pooling blood raises pressure inside the veins, forcing fluid into the surrounding tissue and producing visible swelling. CVI typically worsens as the day goes on. You may notice your ankle looks fine in the morning and progressively puffs up by evening, especially if you’ve been standing. Other signs include legs that feel achy, heavy, or tired; a burning or tingling sensation; nighttime leg cramps; and visible varicose veins.
Over time, untreated CVI can cause the skin on your lower leg to turn reddish-brown as tiny capillaries burst under pressure. The skin may become leathery, flaky, or itchy. In severe cases, the constant fluid buildup creates scar tissue that traps even more fluid, making your calf feel large and hard. Open sores (ulcers) can develop near the ankle. These later-stage changes are preventable with early management, which is why persistent one-sided ankle swelling is worth getting checked even when it doesn’t hurt much.
Deep Vein Thrombosis
A blood clot in one of the deep veins of your leg, known as DVT, is the most urgent cause of sudden one-sided ankle or leg swelling. The clot blocks normal blood flow, causing fluid to back up below the obstruction. DVT most often forms after long periods of immobility, like a long flight, extended bed rest, or recovery from surgery, because your calf muscles aren’t contracting to push blood along. It can also develop after vein damage from surgery, infection, or injury.
The classic symptoms are swelling in one leg, pain or cramping that often starts in the calf, skin that looks red or purple, and warmth over the affected area. Not everyone gets all four symptoms, and some people notice only mild tightness or swelling without obvious pain.
DVT is dangerous because part of the clot can break off and travel to your lungs, causing a pulmonary embolism. If you have leg swelling along with chest pain, difficulty breathing, dizziness, or coughing up blood, that combination requires emergency care immediately. Even without those symptoms, sudden swelling in one leg that appears for no clear reason warrants prompt medical evaluation.
Sprains and Other Injuries
An ankle sprain is one of the most straightforward explanations for swelling on one side. You may have twisted your ankle during exercise, stepped off a curb awkwardly, or rolled it slightly without thinking much of it at the time. The severity of swelling depends on how badly the ligament is damaged.
- Mild sprain: The ligament is stretched and slightly damaged but not torn. You’ll have some pain and tenderness, with modest swelling.
- Moderate sprain: The ligament is partially torn. Noticeable swelling develops, and it hurts to move the ankle.
- Severe sprain: The ligament is completely torn. Swelling is significant, and you may not be able to walk or move the ankle at all.
For mild and moderate sprains, rest, ice, compression, and elevation during the first four to five days helps manage the inflammatory phase of healing. Research comparing this approach to early therapeutic exercise found that gentle strengthening and range-of-motion exercises during the first two weeks improved ankle function faster, though by the one-month mark both groups had similar outcomes. For a severe sprain, you’ll likely need imaging and possibly immobilization.
Gout and Infection
Gout occurs when uric acid crystals accumulate in a joint, triggering sudden, intense inflammation. While the big toe is the most famous target, gout can strike the ankle. A gout flare comes on fast, often overnight, and the joint becomes red, hot, swollen, and exquisitely tender. The pain typically peaks within 12 to 24 hours.
Cellulitis, a bacterial skin infection, can look remarkably similar. The skin becomes red, warm, swollen, and painful, sometimes with spreading redness that extends well beyond the joint. These two conditions can be difficult to tell apart even for clinicians. One important clue: if anti-inflammatory treatments don’t help and symptoms keep worsening, infection becomes more likely. Cellulitis needs antibiotics, while gout is managed by reducing inflammation and lowering uric acid levels over time.
Lymphedema
Your lymphatic system drains excess fluid from tissues back into your bloodstream. When lymphatic vessels are damaged or blocked, protein-rich fluid accumulates in the affected limb. This produces swelling that starts as soft and pitting (you can press a finger in and leave a dent) but gradually becomes firm and non-pitting as the trapped protein stimulates scar-like tissue growth.
Lymphedema commonly affects just one limb. It can develop after surgery or radiation therapy that damages lymph nodes, or it can appear without an obvious cause. A physical sign called the Stemmer sign helps identify it: if you can’t pinch a fold of skin on top of your foot between the second and third toes, lymphatic swelling is likely. Early lymphedema responds well to compression and specialized drainage techniques, but it becomes harder to manage once the tissue firms up.
How Doctors Figure Out the Cause
When you show up with a swollen right ankle, the evaluation usually starts with your history and a physical exam. Your doctor will want to know when the swelling started, whether it came on suddenly or gradually, what makes it better or worse, and whether you’ve had recent surgery, travel, injury, or immobility.
If DVT is suspected, doctors use a risk-scoring system that assigns points based on factors like recent surgery, immobility, cancer treatment, tenderness along the deep veins, calf swelling that’s more than 3 cm larger than your other leg, and pitting edema. A score of zero puts the probability of DVT around 5%, while a score of 3 or higher raises it to roughly 53%.
Ultrasound is the primary imaging tool. For clots in the upper leg veins, compression ultrasound detects DVT with about 96.5% accuracy. For clots below the knee, sensitivity drops to around 57%, though false positives are rare (specificity of nearly 98%). This means a positive result is highly reliable, but a negative scan in the calf doesn’t completely rule out a small clot, and repeat imaging may be needed if symptoms persist.
What You Can Do at Home
For swelling related to mild injury or venous pooling, elevation is your simplest tool. Propping your leg above heart level for 15 to 20 minutes several times a day helps gravity move fluid back toward your core. Compression socks or stockings apply steady pressure that supports your vein valves and reduces fluid leakage into tissues. Regular movement, even short walks or calf raises, activates the muscle pump that pushes blood upward through your veins.
Ice wrapped in a cloth can help in the first few days after an injury. Avoid sitting or standing in one position for long stretches. If you work at a desk, set a reminder to stand and walk briefly every hour. If you’re on your feet all day, take sitting breaks with your legs elevated when possible.
These measures help manage swelling from known minor causes. They don’t replace evaluation for swelling that appears suddenly without explanation, keeps getting worse, involves skin color changes or warmth, or comes with pain in your calf. One-sided ankle swelling that doesn’t resolve within a few days, or that recurs regularly, is worth bringing to your doctor’s attention to rule out DVT, venous insufficiency, or other conditions that benefit from early treatment.