Vascular dilatation is categorized into venous dilatation and arterial dilatation. Venous dilatation may be related to weak venous walls, venous valve insufficiency or prolonged standing; arterial dilatation may be related to aneurysms, severe infections and so on. 1. Venous dilatation (1) Weakness of vein wall: because the vein wall is weak, there are fewer muscle cells and elastic fibers, thus the tension and elasticity of the vein wall are weakened, and then venous dilatation occurs. (2) Venous valve insufficiency: Since venous valves have the function of preventing venous blood from refluxing, when the valves are closed insufficiently, the blood refluxes, thus dilating the veins. (3) Prolonged standing: when standing for a long time, due to the effect of gravity, it may lead to the increase of blood in the veins of the lower limbs, stagnation, and then increase the pressure in the veins, resulting in venous dilatation. (2) Arterial dilatation: such as abdominal aortic aneurysm, intracranial aneurysm, etc., due to the damage of vascular endothelium, resulting in the formation of atherosclerotic plaques, which in turn leads to the gradual dilatation of blood vessels, and the rupture of aneurysm and bleeding may occur in severe cases. In addition, when severe infections occur, a large number of inflammatory factors are released in the patient’s body, and these factors can act on the walls of the arterial vessels, thus causing the arteries to dilate. There are many other causes of vasodilatation, and it is recommended to consult a doctor in a timely manner to clarify the cause and follow the doctor’s instructions for standardized treatment.