The field of medical imaging has been pioneered since 1895 with the discovery of X-rays by the German physicist Roentgen. The application of this technology in clinical medicine has enabled physicians to clearly see the anatomy of some internal organs and organs in vivo and the morphological changes caused by lesions, thus improving the diagnosis of certain diseases. Initially this technology could only show organs and systems with good natural contrast, such as the osteoarticular system and the lungs, but scholars were not satisfied with this and wanted to improve the contrast between organs by artificial means for clearer diagnostic imaging. This led to the emergence of contrast agents, or “contrast agents” as they are commonly known. Once this technique was introduced, it was quickly accepted by physicians and patients as a screening tool for coronary artery disease because of its minimally invasive nature and effectiveness. Currently, the most widely used contrast agent is the water-soluble organic iodine contrast agent injected intravenously under X-ray examination. It is required in CT-enhanced examinations of many sites, certain special contrast examinations (such as pyelogram, etc.) and angiographic (DSA) examinations with digital silhouette. Therefore, the incidence of adverse reactions is relatively high. Foreign data show that the incidence of rapid adverse reactions to non-ionic iodine contrast agents is about 3%, and the incidence of serious adverse reactions is 0.04%. The main adverse reactions of iodine contrast agents include: idiosyncratic reactions and organ toxicity reactions. These reactions are generally unrelated to the dose used, and are difficult to prevent and protect against. Organ toxicity reactions are the nephrotoxicity, cardiotoxicity and thyrotoxicity of iodine contrast agent, which are related to the basal status of the patient’s relevant organs, the charge number of the contrast agent, the dose injected, etc. and can be predicted or prevented. Allergic reactions caused by iodine contrast agents can be divided into rapid-onset and delayed-onset reactions. Those occurring within 1 hour after injection are called rapid-onset reactions, and those occurring from 1 hour to 1 week after injection are called delayed-onset reactions. Depending on the degree of rapid-onset allergic reactions, they can be classified as mild, moderate or severe. The main clinical manifestations of mild reactions include nausea, mild vomiting, urticaria, pruritus, facial edema, etc. They can recover on their own without treatment, or symptomatic treatment can be given accordingly. The main clinical manifestations of moderate reaction include: repeated heavy vomiting, dizziness, mild laryngeal edema, mild tracheal spasm, mild and temporary drop in blood pressure. The principle of treatment is to lie down, administer oxygen, closely observe vital signs, and provide timely symptomatic treatment, such as intramuscular injection of 1:1000 epinephrine, intravenous rehydration, elevation of legs for hypotensive patients, and treatment with antiemetic agents for severe vomiting. Severe reactions are life-threatening, with clinical manifestations of respiratory distress, hypotensive shock, unconsciousness, convulsions, cardiac arrest, etc. First-aid measures should be started immediately. In addition to the aforementioned antispasmodic, anti-allergic, antihypertensive and volume expansion measures, tracheotomy and cardiopulmonary resuscitation should be performed immediately to save the patient’s life. The main manifestation of delayed allergic reaction is skin rash or maculopapular rash, mostly mild to moderate reaction, which is self-healing and can be treated symptomatically. Risk factors for contrast allergy are: patients with a history of asthma, hay fever, drug/food allergy, and especially for patients with a history of iodine contrast allergy; patients treated with interleukin-2 within two weeks have an increased risk of delayed allergic reactions. For patients treated with β-blockers, once a rapid allergic reaction of moderate severity or more occurs, the rescue measures should be changed, and intramuscular epinephrine will not be effective and needs to be replaced with glucagon. Means of prevention of allergic reactions to contrast agents include: (1) Consider substituting other imaging examinations without iodine contrast agents; (2) The use of hypotonic non-ionic contrast agents can significantly reduce the occurrence of adverse reactions, and sometimes patients who are allergic to one iodine contrast agent do not have allergic reactions when applying another iodine contrast agent; (3) Allow patients to stay for 30 minutes after contrast agent injection and leave without problems; (4) After injection Encourage patients to drink more water to promote excretion of the contrast agent; (5) For high-risk patients with a history of allergy, consider prophylactic medication, as recommended by the European Committee for Contrast Agent Safety: 30 mg of prednisolone (or 32 mg of methylprednisolone) orally 12 hours and 2 hours before contrast injection; (6) The value of the iodine allergy test is controversial, and a positive result does not predict the certain occurrence of an allergic reaction, nor (6) The value of the iodine allergy test is controversial. A positive result does not predict the occurrence of an allergic reaction, nor does it predict the severity of the reaction; a negative result also has the possibility of a serious reaction (including a lethal reaction); the allergy test itself can lead to a serious allergic reaction. Therefore, some scholars suggest that the allergy test should be abolished, and in addition to relevant prevention for high-risk patients, all patients should be closely observed during the whole process of imaging examination with contrast injection, and the examination room should be equipped with resuscitation drugs and facilities for timely treatment and assistance in case of problems. In conclusion, both medical personnel and patients should have a comprehensive understanding of the problems that may be brought about by iodine contrast agents, should take preventive measures for high-risk patients, should pay close attention to observation during the application process, and should correctly handle the possible adverse reactions brought about by contrast agents.