Fluid Retention

Fluid Retention (Edema): Why the Body Accumulates Water

Fluid retention, or edema, is a condition in which excess fluid builds up in the body's tissues. It is most commonly noticeable in the feet, ankles, legs, and hands, because gravity "pulls" the fluid downward. Edema can be a temporary and harmless phenomenon caused by lifestyle or hormonal fluctuations, or it can be a symptom of a serious disease. Understanding the mechanism of its development helps identify possible causes.

How does edema develop?

Our body constantly maintains fluid balance between the blood vessels (capillaries) and the surrounding tissues. This balance is regulated by a complex interplay of hydrostatic (blood pressure) and oncotic (protein‑generated) pressure. Edema occurs when this balance is disturbed and fluid leaks from the capillaries into the tissues faster than the lymphatic system can remove it.

Physiological (benign) causes of edema

• Prolonged standing or sitting: Gravity makes it harder for blood to return from the legs to the heart, raising venous pressure and promoting fluid leakage into tissues.
• Heat: In hot weather, vessels dilate, which also facilitates fluid leakage.
• Pregnancy: An enlarged uterus compresses veins, and hormonal changes promote fluid retention. More details can be found in the article "Edema During Pregnancy".
• Excessive salt intake: Salt (sodium) causes the body to retain water.

Pathological causes of edema

Sometimes edema is a symptom of a systemic disease.

• Heart failure: The heart cannot pump blood efficiently, leading to blood pooling in the veins.
• Kidney disease: The kidneys cannot eliminate sufficient sodium and water from the body.
• Liver disease: Liver cirrhosis reduces the level of the protein albumin in the blood, disrupting oncotic pressure.