The body is made of millions of cells, most of them linked together to form tissues. The cells are filled with (and surrounded by) fluid. Therefore, the majority of a person's body weight (about 65%)consists of water.

What is edema?

Edema is fluid retention and it occurs when there is too much fluid (mainly water) in the body's tissues, causing swelling to occur in the affected area. The swelling is usually related to the venous (veins) system, or the lymphatic system (tubes that carry lymph, a fluid that helps fight infection and clear fluid).

Edema can affect:

• the hands, arms, feet, ankles and legs (swelling is most common in these areas),
• the brain (known as cerebral edema), and
• the eyes (known as macular edema).

Normally, the amount of water in the body is determined by the difference between fluid that is taken in and fluid that is taken out (discharged). Fluid is taken into the body by eating and drinking, and by water produced by bodily processes. It is discharged from the body in the form of urine, feces, sweat, and non-visible perspiration, for example, when breathing out..

Factors such as the surrounding air temperature, and strenuous exercise, can affect the amount of water that is taken in and out of the body.

In people with edema, the excess fluid can be caused by a number of factors. This is because edema is not a condition itself, but is often a symptom of an underlying condition. For example, it can be a sign of kidney disease, or lymphedema. Lymphedema is a chronic swelling that occurs when lymph fluid does not fully drain away from the tissues.

Edema can also sometimes be caused by lifestyle factors, such as pregnancy, or a high dietary salt intake.