Swelling in the ankles, often called edema, is caused by an accumulation of excess fluid in the tissues of the lower legs and feet. This fluid buildup can result from a variety of reasons including:

• Prolonged sitting or standing in the same position
• High salt intake in the diet
• Being overweight or pregnancy
• Certain medications such as blood pressure drugs, contraceptive pills, antidepressants, or steroids
• Injuries like sprains or strains
• Infections or insect bites
• Problems with the kidneys, liver, or heart
• Blood clots or venous insufficiency, where veins have trouble returning blood to the heart
• Hormonal changes (e.g., during pregnancy or menstruation)
• Lymphatic system blockages (lymphedema)
• Chronic conditions such as heart failure, kidney disease, or liver disease
• Other factors like aging, long airplane flights or car rides, and hot weather

In addition, inflammation caused by immune response to irritants or injury can also cause ankle swelling. Treatments and relief usually depend on the underlying cause but can include elevating the legs, exercising gently, wearing comfortable shoes, reducing salt intake, and avoiding prolonged immobility.