If you’ve noticed that only one ankle is swollen, you may wonder why the other ankle looks perfectly normal. Sometimes the explanation is a minor injury or inflammation. Other times, unexplained swelling can indicate a problem with circulation, an infection, or a blood clot.

The location, timing, and associated symptoms provide important clues. For example, swelling after twisting your ankle suggests a different problem than swelling that appears suddenly without an injury.

The most important point: New, unexplained swelling in one ankle should receive prompt medical assessment, particularly if it is painful, warm, red, or spreading into the calf. You cannot reliably rule out a blood clot based on appearance alone.

What Causes Only One Ankle to Swell?

Swelling develops when fluid accumulates in surrounding tissues or when inflammation causes an area to become enlarged.

When only one ankle is affected, clinicians consider conditions involving that particular joint, its surrounding tissues, or the circulation of the affected leg.

Common possibilities include:

• Ankle sprains and other injuries
• Tendon inflammation
• Gout or other joint inflammation
• Cellulitis and joint infections
• Venous insufficiency
• Lymphedema
• Deep vein thrombosis (DVT)

The pattern of swelling helps guide the evaluation, but symptoms alone cannot establish a diagnosis.

For a broader explanation of swelling throughout the leg, read our guide to leg swelling, blood clots, and fluid retention.

1. Ankle Sprain or Injury

An ankle sprain occurs when ligaments supporting the joint become stretched or torn, commonly after the foot rolls inward or outward.

Symptoms may include:

• Swelling around the ankle joint
• Pain after twisting the foot
• Tenderness over injured ligaments
• Bruising
• Difficulty walking
• Reduced ankle movement

Swelling can appear shortly after an injury or increase over several hours.

Mild sprains often improve with protection, relative rest, ice, and elevation. However, fractures and significant ligament injuries may initially resemble ordinary sprains.

When does a swollen ankle need an X-ray?

Clinicians commonly use the Ottawa Ankle Rules to help decide whether imaging is necessary after an acute ankle injury.

An ankle X-ray is generally indicated when there is pain in the malleolar region together with qualifying bone tenderness over either malleolus or inability to take four steps immediately after the injury and during evaluation.

These rules are not appropriate for every patient or situation. Significant deformity, impaired circulation, neuropathy, or other concerning findings require individualized assessment.

2. Tendonitis or Tendon Injury

Tendons connect muscles to bones and help control ankle movement.

Inflammation or injury involving the posterior tibial, peroneal, or Achilles tendons can cause localized pain and swelling.

Typical clues include:

• Pain during walking or exercise
• Tenderness along a tendon
• Swelling behind or beside the ankle
• Symptoms that worsen with repeated movement

Posterior tibial tendon problems often affect the inner ankle, while peroneal tendon disorders commonly cause symptoms along the outer ankle.

Treatment depends on severity and may include activity modification, supportive footwear, bracing, or physical therapy. Suspected tendon rupture requires prompt evaluation.

3. Gout or Other Joint Inflammation

Gout is an inflammatory form of arthritis caused by monosodium urate crystal deposits within a joint.

Although gout commonly affects the big toe, it can also involve the ankle.

Symptoms may include:

• Sudden, intense joint pain
• Significant swelling
• Redness or warmth
• Extreme tenderness
• Difficulty bearing weight

Gout attacks often develop rapidly, sometimes overnight.

However, a hot, swollen ankle should never automatically be assumed to be gout. Septic arthritis, a serious joint infection, can produce similar symptoms.

A clinician may recommend joint-fluid testing when infection is a concern. Treatment for gout differs substantially from treatment for an infected joint.

4. Cellulitis or Joint Infection

Cellulitis is a bacterial infection involving the skin and underlying soft tissues.

It can develop after a cut, insect bite, wound, or another disruption of the skin barrier.

Possible symptoms include:

• Swelling affecting one ankle or foot
• Redness or darker skin discoloration
• Warmth
• Tenderness
• Spreading skin changes
• Fever or chills

Cellulitis usually requires antibiotics selected according to the clinical findings and patient risk factors.

A deeper infection involving the ankle joint, called septic arthritis, is more urgent. Severe joint pain, marked limitation of movement, fever, or inability to bear weight can raise concern.

Suspected septic arthritis requires emergency evaluation, because delayed treatment can permanently damage the joint.

5. Venous Insufficiency

Veins contain valves that help move blood from the legs toward the heart.

When these valves become weakened or damaged, blood can pool in the lower extremities. This is called chronic venous insufficiency.

Symptoms may include:

• Swelling that increases later in the day
• Ankle heaviness or aching
• Varicose veins
• Skin discoloration near the ankle
• Improvement with elevation

Venous insufficiency can affect both legs, but one side may be noticeably worse.

A healthcare professional may recommend a venous ultrasound to evaluate circulation and determine whether additional treatment is necessary.

Compression stockings can help some patients, but they should not be started indiscriminately when there is unexplained acute swelling, possible DVT, or significant arterial circulation disease.

6. Lymphedema

The lymphatic system helps drain excess fluid from body tissues.

When lymphatic drainage is impaired, fluid can accumulate and cause persistent swelling.

Lymphedema may develop after lymph-node surgery, radiation treatment, infections, or other conditions affecting lymphatic vessels. Sometimes the cause is unclear.

Clues include:

• Persistent swelling of one foot, ankle, or leg
• A feeling of heaviness
• Tightness of the skin
• Gradual thickening of the skin
• Swelling that may initially improve with elevation

Lymphedema often requires long-term management, including specialized compression therapy and skin care.

Other important causes of swelling should be evaluated before attributing new unilateral swelling to lymphedema.

7. Deep Vein Thrombosis (Blood Clot)

A deep vein thrombosis occurs when a blood clot forms inside a deep vein, usually in the leg.

DVT is particularly important because a clot can sometimes travel to the lungs, causing a potentially life-threatening pulmonary embolism.

Possible symptoms include:

• New swelling in one leg
• Calf or leg pain
• Tenderness
• Warmth
• Redness or unusual discoloration

Some people have relatively mild symptoms, but the most important emergency to rule out is a blood clot in the leg also known as deep vein thrombosis (DVT). If you’re unsure what a blood clot actually feels like, read our guide to blood clot symptoms in the leg and the warning signs you shouldn’t ignore to understand how DVT may present and when to seek emergency care.

A DVT does not always produce dramatic swelling, and the absence of calf pain does not exclude it.

Risk factors include recent surgery, prolonged immobility, previous blood clots, active cancer, pregnancy or the postpartum period, and certain estrogen-containing medications.

Read our calf pain versus blood clot guide for additional information about symptoms and DVT risk factors.

New unexplained one-sided ankle or leg swelling warrants prompt medical assessment, even when pain is absent.

What If Only One Ankle Is Swollen but Doesn’t Hurt?

Painless swelling may be associated with venous insufficiency, lymphedema, dependent edema, or medication-related fluid retention.

However, pain is not required for a serious condition.

A blood clot can occasionally produce swelling without significant tenderness. Similarly, early infection or other circulatory problems may not initially cause severe discomfort.

If the swelling is new, unexplained, persistent, or worsening, arrange prompt medical evaluation rather than assuming that the absence of pain means it is harmless.

What If One Ankle Swells After Standing All Day?

Prolonged standing allows gravity to increase fluid pressure in the lower legs.

This can cause swelling that becomes more noticeable toward the evening.

Dependent swelling commonly affects both ankles, although preexisting vein problems or previous injuries may make one side more noticeable.

If one ankle suddenly becomes significantly larger than the other, do not automatically attribute it to standing.

Travel-related swelling can follow a similar pattern. See our article about swollen feet after flying and when to seek care.

How Do Doctors Diagnose One Swollen Ankle?

The evaluation starts with a medical history and physical examination.

Your clinician may ask:

• When did the swelling begin?
• Was there a recent injury?
• Is the ankle painful, red, or warm?
• Does swelling improve overnight?
• Is the calf also swollen?
• Have you recently traveled, undergone surgery, or been immobilized?
• Do you have a history of blood clots, gout, or circulation problems?

The examination may include assessing the ankle joint, skin, tenderness, range of motion, pulses, sensation, and swelling throughout the leg.

Depending on the findings, testing may include:

Ankle X-ray: To evaluate suspected fracture or other bone injury.

Venous duplex ultrasound: To investigate possible DVT or certain venous disorders.

Blood tests: To investigate infection, inflammation, or underlying medical conditions when appropriate.

Joint aspiration: To analyze fluid when septic arthritis or crystal arthritis is suspected.

Not every swollen ankle requires all these tests. The appropriate evaluation depends on the clinical presentation.

When Should You Go to Urgent Care or the ER?

Seek same-day medical assessment if:

• One ankle becomes swollen without an obvious explanation.
• Swelling is new and persistent.
• The ankle is red, warm, or increasingly painful.
• Swelling extends into the calf.
• You have blood-clot risk factors.
• You have diabetes and develop new ankle or foot swelling.
• Swelling becomes substantial after an injury.

Urgent care may be an appropriate starting point when symptoms are stable, but suspected DVT may require immediate access to ultrasound at another facility.

Go to the emergency department immediately if:

• You have severe ankle pain with fever or a suspected infected joint.
• Your foot becomes pale, cold, blue, numb, or suddenly weak.
• There is major deformity or a serious injury.
• Swelling or pain becomes rapidly severe.

Call 911 if leg swelling occurs with chest pain, sudden shortness of breath, coughing up blood, fainting, or other symptoms suggesting a pulmonary embolism.

What Can You Do at Home?

Home treatment is appropriate only when a serious cause has been reasonably excluded or a clinician has determined that self-care is suitable.

For a confirmed minor injury, measures may include:

• Temporarily reducing painful activity
• Applying a wrapped cold pack for 15–20 minutes at a time
• Elevating the ankle
• Using appropriate support or bracing
• Gradually returning to activity as symptoms improve

Avoid tight compression or vigorous massage when the cause of unexplained unilateral swelling is uncertain.

Do not take leftover antibiotics, prescription blood thinners, or diuretics to treat swelling without medical guidance.

The treatment should address the underlying cause rather than simply attempting to reduce the swelling.

Frequently Asked Questions

Why is my left ankle swollen but not my right?

Possible causes include an old injury, tendon inflammation, venous insufficiency, infection, lymphedema, or DVT. New unexplained swelling should be assessed promptly.

Can a blood clot cause only ankle swelling?

A DVT more commonly causes swelling involving the calf or leg, but symptoms vary. Ankle swelling alone cannot confirm or exclude a clot.

Can gout cause ankle swelling without an injury?

Yes. Gout can cause sudden inflammation of the ankle without trauma, typically with significant pain and warmth. Infection must also be considered.

How long should ankle swelling last?

Mild swelling after a minor injury may improve over days, although complete recovery can take weeks. Persistent or worsening swelling requires reassessment. New unexplained one-sided swelling should not simply be watched for several days without medical advice.

Should I wear compression socks for one swollen ankle?

Not until the cause is reasonably established and compression is appropriate for your circulation and medical history. Compression can be useful for selected venous or lymphatic conditions but is not a substitute for evaluating possible DVT.

The Bottom Line

Swelling in only one ankle can result from injuries, tendon disorders, gout, infection, venous insufficiency, lymphedema, or a blood clot.

The most useful clues are whether swelling began after an injury, whether it is painful or warm, and whether it extends into the calf.

New unexplained one-sided ankle swelling deserves prompt medical evaluation. Chest pain, breathing difficulty, fainting, or signs of suddenly impaired circulation require emergency care.

Sources

1. National Health Service. Swollen ankles, feet and legs (oedema). NHS.
2. American College of Radiology. ACR Appropriateness Criteria: Acute Trauma to the Ankle.
3. Centers for Disease Control and Prevention. About Venous Thromboembolism (Blood Clots).
4. MedlinePlus. Foot, Leg, and Ankle Swelling.
5. Mayo Clinic. Edema: Symptoms and Causes.
6. Cleveland Clinic. Chronic Venous Insufficiency.

Medical disclaimer: This article provides general health education and is not a substitute for individualized diagnosis or treatment. Seek professional medical evaluation for new, unexplained, or concerning symptoms.