What is chronic pain? Chronic pain is pain that lasts for more than 3 months, is frequent at least once a week, is accompanied by unpleasant sensations and emotional experiences, and may be accompanied by existing or underlying tissue damage. How does chronic pain develop? Pain that is less than 1 month old is called acute pain. Acute pain is a protective response of the body to itself that prevents harmful movements, helps maintain homeostasis in the early stages of acute illness and injury, alerts the patient to seek medical attention, and facilitates the diagnosis and treatment of the disease. There is a positive biological role. In the face of acute pain, on the one hand, one should actively search for the cause and diagnose and treat the cause, on the other hand, effective analgesic treatment on the basis of definite diagnostic treatment is also of great importance to relieve pain and provide quality of life. Pain greater than 1 month but less than 3 months is called subacute pain, which is a process of transition from acute pain to chronic pain, and at this stage, active analgesic treatment can also slow down or reverse the transition to chronic pain. Pain greater than 3 months is called chronic pain. Chronic pain has no benign effects and only negative effects. Chronic pain that cannot be relieved can prolong the recovery from disease and can even have an impact on immunity. Chronic pain can develop central sensitization and generalization, form pain memories, and even convert into refractory pain. Moreover, chronic pain is often associated with anxiety and depression, and many of the chronic pain patients seen have anxiety and depressive states. In a patient with a 4-year history of postherpetic neuropathic pain, he had lost confidence in treatment at the time of his first visit and had been trying to end the pain by committing suicide. Even this bad mood would radiate among the patients and their families. Therefore, it is now generally accepted that acute pain is a symptom, while chronic pain is a category of disease.