Oedema is the retention of fluid in the tissues of the body. In a healthy child’s body, the cells function properly by controlling the movement of three main electrolytes within the body, moving sodium out of the cell and potassium and magnesium into the cell with the help of a pump known as the sodium-potassium pump.

In malnourished children, like Fatima on the right, the cells lose their ability to keep this balance, leading to the loss of potassium and magnesium from within the cells; and the movement of sodium into the cells, causing fluid retention (oedema).