Why Your Foot or Ankle Is Swollen and What to Do for It

Swelling in the ankles and feet is a common problem. This swelling is often caused by a buildup of fluid, which is called edema. Edema is common in the feet, ankles, and legs, and often only one ankle is swollen.

Among the range of causes are those linked to a chronic condition like infection, arthritis, or a mass or tumor that affects just one foot and leg. When only one ankle is swollen and it happens suddenly, it can be due to:

• A sprain or fracture (trauma)
• A blood clot (deep vein thrombosis)
• Infection
• Insect bites

In some cases, as with pregnancy or medication use, ankle and foot swelling may be temporary or reversible. Other conditions (often chronic) that are more typically involved when both ankles and feet are swollen can include:

• Heart disease
• Kidney or liver failure
• Obesity
• Obstructive sleep apnea

This article can help you figure out what's causing your foot and ankle swelling. It discusses some of the common causes of swelling and other symptoms you might experience with the condition.

Trauma

Foot and ankle injuries are among the most common reasons for a healthcare provider visit. Those that cause swelling include:

• Ankle sprains
• Torn tendons
• Fractures (broken bones)

Those tend to be sudden injuries. Overuse can cause swelling as well, but these injuries tend to come on more gradually. Overuse injuries include:

• Tendonitis
• Bursitis
• Ligament or muscle strains

You're more likely to injure your feet or ankles if you play sports, exercise a lot, increase your activity level, or introduce a new exercise or activity, such as walking or running on a new type of terrain.

Arthritis

Arthritis, or joint inflammation, can cause swelling in the foot or ankle. Osteoarthritis is a common form of arthritis that may cause occasional swelling. It usually happens in a single joint.

Gout is another form of arthritis that typically produces a very painful, red, swollen joint. The big toe is most common but gout can also affect the ankle or other joints in the foot.

Some autoimmune diseases cause swelling and arthritis that affect both feet or ankles. These include:

• Rheumatoid arthritis
• Psoriatic arthritis
• Lupus
• Reactive arthritis

In each of these conditions, the immune system attacks healthy tissues, leading to pain, inflammation, and damage.

Septic arthritis occurs due to a bacterial infection in an arthritic joint, often in people who have:

• Implanted medical devices (joint replacements)
• A condition like gout that increases the risk due to chronic joint damage
• Underlying immune system compromise, such as human immunodeficiency virus (HIV) 

Septic arthritis is most often seen in children and older adults. It can affect just one ankle, or it can more widely affect the body. Septic arthritis can prove fatal and requires immediate medical care.

Vein Problems

Problems with leg veins, such as varicose veins or spider veins, often cause swelling in the lower legs.

Veins return deoxygenated blood (blood without oxygen) to the heart. They may become damaged as we age and lead to swelling of the legs and ankles.

This is known as venous insufficiency. The most common signs include:

• One leg that periodically swells (although both can be affected)
• Varicose or spider veins on the swollen leg or ankle
• A brown or darker brown skin discoloration that develops over time

Blood Vessel Blockage

Pain and swelling in one lower leg can be signs of a circulatory problem. This is often due to a blood clot known as deep vein thrombosis (DVT), but it can have other causes including peripheral artery disease and compartment syndrome (often associated with an injury or overuse).

Deep Vein Thrombosis

Deep vein thrombosis (DVT) can lead to life-threatening complications and requires immediate medical attention. It is often caused by inactivity. Some situations can make it difficult for you to move your legs frequently and may put you at risk for a DVT, such as:

• Air travel
• A leg cast
• An illness requiring bed rest

Other risk factors include:

• Obesity
• Smoking
• Pregnancy
• Birth control medications
• Inherited blot clotting disorders

If you take birth control medications, your risk of DVT is further increased if you also smoke or have an inherited blood clotting disorder known as Factor V Leiden.

Peripheral Artery Disease

With peripheral artery disease (PAD), one or more of the arteries that carry blood to the lower extremities can become blocked due to underlying vascular (blood vessel) disease. This causes fluid to back up and can affect the ankle and foot.

Chronic disease is the most common reason for PAD, but PAD also can occur in people who experience a traumatic injury or are exposed to radiation. In some cases, people diagnosed with PAD also have limited or disordered lymph function. Lymphatic blockage can also contribute to ankle or foot swelling.

Compartment Syndrome

Fluid will sometimes build up around the muscle at the ankle or other site, either due to exertion or because of a sudden injury. It can cause swelling due to the pressure which damages tissue. The forearm and the lower leg (at the shin bone) are common injury sites in people who experience sports-related compartment syndrome.

Pain due to the swelling is common. Compartment syndrome needs to be treated quickly to avoid permanent tissue death and damage from sudden-onset swelling.

It's also possible for compartment syndrome to be a chronic condition, with studies suggesting the lower leg is more often affected by chronic forms of the exercise-related diagnosis.

Infection

Skin infection is a common cause of swelling in one foot. It's usually accompanied by pain and redness. Swelling is often seen with:

• Infected ingrown toenails (onychocryptosis)
• Infections between toes
• Severe forms of athlete's foot

Other ways infection can occur in the feet include trauma, such as puncture wounds or nail injuries, and wounds caused by diabetes. Although much less common, an infection can occur in joints even without direct trauma.

The shape of feet in some people also is marked by certain changes, such as flat feet or arches, that can contribute to the increased likelihood of foot or ankle swelling.

Lymphatic Blockage

Lymphedema is a swelling in your foot or lower leg due to blocked flow of lymph fluid. This can occur due to primary lymphedema, or because of another condition that leads to the swelling.

Primary causes are rare and occur in about one in every 100,000 people in the United States. It can be an inherited disorder; Milroy disease, for example, is a genetic condition that occurs when someone is born with very small (or no) lymph vessels.

Secondary causes of lymphedema affect one in 1,000 people, most often due to chronic venous insufficiency but also due to PAD.

Pregnancy

Swelling in both ankles and feet during pregnancy is common. It's caused by a combination of:

• Pregnancy hormones
• Increased blood volume
• The growing uterus which puts pressure on blood vessels in the legs

You may have swollen legs after giving birth, as well. The swelling can last for a few days after delivery.

If you have swelling during pregnancy, you should let your healthcare provider know.

Other Medical Conditions

Some medical conditions that can cause swelling in both legs include:

• Heart disease
• Kidney disease
• Liver disease
• Chronic sleep apnea
• Complications of diabetes
• Premenstrual syndrome (PMS)

Medications

Some prescription medications can cause swelling in both legs, as well, including:

• Birth control pills
• Estrogen replacement drugs
• Testosterone drugs
• Corticosteroids
• Anti-inflammatory drugs (NSAIDs)
• Certain blood pressure medicines
• The diabetes drugs Avandia (rosiglitazone maleate) and Actos (pioglitazone)

Drinking alcohol can also cause swelling in the ankles or feet.

Summary

Swelling of the ankles and feet is fairly common. You may experience this swelling for a variety of reasons. Sometimes swelling may occur because of trauma or an injury. You may have swollen ankles and feet because of arthritis or certain medical conditions.

Pregnant women may experience foot and ankle swelling as well. Other people may have swollen ankles and feet because of a blood clot or vein problems. For this reason, it's important to seek immediate medical attention if your ankles and feet suddenly begin to swell for no apparent reason.