The reason for swelling after being bitten by a snake may be that the capillary permeability is elevated and there is extravasation of tissue fluid, resulting in edema. After the snake bites the organism, there will be snake venom into the tissues, and under the stimulation of snake venom, the permeability of local capillaries is elevated, thus there is an exudation of tissue fluid, causing edema. In addition, snake venom has a strong toxic effect on tissue cells, and after the necrosis of tissue cells, the mononuclear phagocytosis system of the organism is activated, and under the stimulation of inflammatory factors, the permeability of capillaries is further increased, and the edema of tissues becomes more obvious. After being bitten by a snake, you need to immediately expel the venom from the body and compress the blood vessels to prevent the spread of venom, and send the nearest hospital for antitoxin injection to avoid life-threatening injuries.