For patients with bilateral lower extremity edema, there are many reasons. 1. renal edema, especially in patients with acute nephritis or nephrotic syndrome, can lead to edema due to increased capillary permeability of the kidneys. 2. cardiogenic edema, when right heart failure occurs in various heart diseases, it can cause an increase in intravenous pressure, resulting in bilateral lower extremity edema, which can be characterized as light in the morning and heavy in the evening. 3. edema caused by liver lesions, such as liver cirrhosis, in which the high pressure of the portal vein obstructs blood flow, and the increased pressure causes liver failure. 4. When the right heart failure occurs in various heart diseases, it can cause the increase of pressure in the veins, which can lead to edema of both lower extremities. 4.Idiopathic edema of women, mainly related to the high level of female estrogen. 5.Filariasis and other diseases, which cause local lower extremity edema, can cause edema due to obstruction of lymphatic vessels.