Edema can occur when the small blood vessels (capillaries) leak fluid into the surrounding body tissue. This may happen as a result of increased pressure in (or damage to) the capillaries.

If your capillaries start leaking, your kidneys will store more sodium and water than normal in order to make up for the lost fluid. As a result, the amount of blood circulating through your body is increased, causing the capillaries to leak even more, and the surrounding tissue to swell.

Edema can be caused by:

• immobility , for example either sitting or standing for long periods of time,
• hot weather,
• exposure to high altitudes,
• burns,
• menstruation,
• pregnancy,
• the contraceptive pill,
• medication , such as high blood pressure medicine,and corticosteroids, or
• salty foods .

In more serious cases, edema can be caused by:

• kidney disease,
• heart failure,
• chronic lung disease,
• thyroid disease,
• liver disease , such as cirrhosis,
• diabetes,
• arthritis , or
• malnutrition .

Edema in the leg may be caused by:

• blood clots,
• varicose veins,
• infection and inflammation,
• lymphedema , which is a chronic swelling that occurs when lymph fluid does not fully drain away from the tissues, or rarely
• a growth or cyst .