Oedema

Oedema is fluid retention. 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).

Oedema can affect:

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

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, faeces, 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 oedema, the excess fluid can be caused by a number of factors. This is because oedema 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 lymphoedema. Lymphoedema is a type of chronic swelling that occurs when the lymph fluid doesn't fully drain away from the tissues.

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