Feet and ankles usually swell when fluid builds up in the tissues (edema), and this can range from harmless to medically serious. Common triggers include everyday issues like standing too long, but also conditions involving the heart, kidneys, liver, veins, joints, or injury.

Everyday, Less-Serious Causes

These causes are very common and often temporary, especially if both feet/ankles are puffy by the end of the day.

  • Standing or sitting too long (work shifts, long flights, road trips) can let blood pool in the lower legs and cause mild swelling.
  • High salt intake makes the body retain fluid, which can collect in feet and ankles.
  • Being overweight puts extra pressure on leg veins and worsens fluid buildup.
  • Pregnancy often causes leg and ankle swelling due to hormone changes, more blood volume, and pressure from the uterus.
  • Hot weather widens blood vessels, letting more fluid leak into surrounding tissues and causing puffy feet.

Injuries and Joint Problems

Swelling that starts after a specific event or in just one foot/ankle often points to a local problem.

  • Sprains, strains, torn tendons, or fractures can all cause one ankle or foot to swell, usually with pain and trouble walking.
  • Overuse injuries like tendonitis or bursitis develop more slowly and may cause aching plus swelling around the joint.
  • Arthritis (including osteoarthritis or gout) can make one or more foot or ankle joints red, stiff, and swollen.

Circulation and Vein Issues

When blood or lymph fluid cannot flow properly back up the legs, swelling is a key warning sign.

  • Chronic venous insufficiency and varicose veins make it harder for blood to return to the heart, so it pools in the lower legs and feet.
  • Blood clots in leg veins (including deep vein thrombosis) can cause sudden swelling, usually in one leg, sometimes with pain, warmth, or color change—this is an emergency.
  • Lymphedema (blocked or damaged lymph vessels) leads to chronic, often firm swelling and sometimes skin thickening.

Heart, Kidney, and Liver Conditions

Whole-body fluid balance problems often show up first as swollen feet and ankles.

  • Heart failure can cause fluid to back up in the veins so the lower legs, feet, and ankles become puffy, often along with shortness of breath or fatigue.
  • Kidney disease makes it harder to remove extra fluid and salt, which then accumulates in tissues, including the lower limbs.
  • Liver disease can lower blood levels of important proteins like albumin, letting fluid leak into tissues and cause swelling in the legs (and sometimes abdomen).

Medications, Infections, and Other Causes

Some additional, often overlooked triggers can also answer what causes feet and ankles to swell.

  • Certain medicines, such as some blood pressure drugs, hormones, antidepressants, and steroids, may cause fluid retention and ankle swelling.
  • Skin and soft-tissue infections (like cellulitis or erysipelas) can cause painful, warm, red swelling, usually on one side.
  • Inflammatory or autoimmune diseases (such as rheumatoid arthritis or lupus) may cause painful, symmetric swelling in both feet or ankles.

Information gathered from public forums or data available on the internet and portrayed here.