Edema is swelling of any organ or tissue due to accumulation of excess fluid. Edema has many root causes, but its common mechanism is accumulation of fluid into the tissues.

Types of edema are pitting edema and non-pitting edema. The former is present if pressing of the affected body part creates a small pit that disappears within a few seconds. Non-pitting edema is not compressible.

Causes of edema are:

1. high hydrostatic pressure of the veins, leading to poor reabsorption of fluid:

• venous obstruction
• congestive heart failure
• varicose veins

2. low oncotic pressure:

• cirrhosis
• malnutrition
• nephrotic syndrome

3. inflammation:

• allergic conditions
• any other form of inflammation (tumor - or swelling - is one of the main characteristics of inflammation)