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Why do legs swell?

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Fluid retentionInjury or infectionBlood clotsAgeMedication side effectTreatment optionsSummary
Legs can swell for many reasons. A swollen leg may result from an infection or a blood clot. If both legs are swollen, this may suggest fluid retention or another underlying condition.
Medically reviewed by Mia Armstrong, MD
Updated on

Aging, fluid retention, and injuries are potential reasons for one or both of your legs swelling.

If you experience recurrent swelling that doesn’t improve in a few days, or the swelling is causing you discomfort, then consider speaking with a healthcare professional.

It’s not always possible to diagnose the cause of a swollen leg with a simple physical examination. You may need diagnostic tests to help identify the underlying cause of the swelling in your legs.

Several reasons that you may experience swollen legs include:

Fluid retention

Fluid retention can cause swelling in one or both of your legs.

This type of swelling is typically only noticeable when a person accumulates about 2.5–3 liters of fluid in their legs.

Fluid retention and swelling can occur for many reasons, including:

Swelling of the arms and legs is a common side effect of pregnancy.

Swelling occurs because the body produces more fluids during pregnancy, leading to fluid retention.

Injury or infection

Swelling and bruising in your leg may be a sign of an injury. Swelling occurs when the body sends fluids containing white blood cells, such as the white cells that fight infections, to the injured area.

Once the injury starts improving, the swelling typically goes down.

An infection can also cause swelling for the same reason. For example, if you have a bacterial infection like cellulitis, you may experience swelling, tenderness, and redness in your leg.

Blood clots

If you have swelling in one leg, you may have a blood clot disrupting blood flow in your blood vessels.

This condition is known as deep vein thrombosis (DVT). If you have a DVT, you may experience symptoms such as:

  • tenderness of the swollen area
  • fever
  • pain inside the leg
  • skin redness
  • veins showing on the surface of your skin
  • discoloration of the skin

If you have symptoms of DVT, it’s important to get immediate medical attention.


As you age, you’re more likely to experience leg swelling. A 2021 survey-based study found that about 19–20% of people over age 54 experience leg swelling.

One of the most common causes of leg swelling in people over 50 years is venous insufficiency, a condition involving a lack of blood flow in the veins.

Medication side effect

Taking certain medications can cause fluid retention and swelling in the legs as a side effect.

Medications that may cause leg swelling include:

  • calcium channel blockers and other vasodilators
  • endocrine drugs, such as estrogen or progesterone
  • antidepressants
  • proton pump inhibitors
  • diazoxide
  • certain drugs for Parkinson’s disease
  • nonsteroidal anti-inflammatory drugs

If you experience swelling in your legs after taking one of these medications, consider speaking with a healthcare professional. They may recommend changing your dosage or alternative medication.

Treatment options

Person laying down with their legs elevated on a pillow.
nito100/Getty Images

Leg swelling treatment depends on the underlying cause.

  • Injury: Applying cold packs, elevating your leg above the level of your heart, and wearing compression socks may help improve swelling.
  • Infection: You may need antibiotics to treat a bacterial infection causing swelling in your leg.
  • Fluid retention: A healthcare professional may prescribe diuretic medications such as spironolactone (Aldactone) or furosemide (Lasix) to limit fluid retention and swelling.
  • DVT: Anticoagulant medications can help dissolve and help prevent the formation of blood clots. These may include:
    • rivaroxaban (Xarelto)
    • apixaban (Eliquis)
    • low molecular weight heparin (Lovenox)

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Leg swelling can occur for several reasons, such as injuries, infections, and blood clots, which can typically cause swelling in only one leg. Still, fluid retention is more likely to cause swelling in both legs.

Treating leg swelling involves treating the underlying cause. A healthcare professional can determine why you have leg swelling and recommend the right treatment option.

Download the free Optum Perks Discount Card to save up to 80% on some prescription medications.

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