Whether or not blood donation is harmful to the body needs to be judged differently according to different groups of people, and cannot be generalized. For most normal people, for example, a normal 50-70 kg adult usually has 4,000-5,000 ml of blood in his body, and a one-time blood donation of 200-400 ml, which only accounts for 1/10-1/25 of the total blood volume, will not cause any harm to the body and can basically return to normal within a week. Some people feel uncomfortable after donating blood, mostly due to mental tension and eating too little before donating. Special groups such as chronically ill patients or menstruating women may feel unwell due to blood donation and are not recommended to donate blood. In addition, after blood donation, patients should eat a light and nutritious diet, avoid spicy and stimulating foods, avoid exertion and take rest.