Pain is an unpleasant somatic sensory and emotional experience associated with tissue damage or with potential tissue damage. Although everyone dislikes pain, it is an integral part of the normal human sensory experience. Whether we like to admit it or not, pain plays a very important role in our lives. Without pain, we would not know to avoid danger, and some would even embark on a path of no return to harm themselves. Pain, like fever, is a warning sign that we are “sick”. When we get a needle in our finger or a local tissue injury or inflammatory reaction, our body responds to the injury by causing a series of defensive responses to protect the body from harm. For example, acute trauma, acute abdominal pain, acute chest pain, inflammatory pain, and other types of pain indicate that tissue damage has occurred in the body, requiring us to seek medical attention in a timely manner. However, if the pain is recurrent or persistent for a long time and progresses from acute to chronic, it loses its significance as a warning signal, and then the pain itself becomes a disease. For example, recurrent headache, neck, shoulder, back and leg pain, bone and joint pain, post-herpetic neuralgia, trigeminal neuralgia, rheumatologic pain, cancer pain, etc., not only bring physical and mental pain to the body, but also seriously affect people’s normal life, study and work. From the duration of pain, there are acute pain, subacute pain and chronic pain. Pain within 1 month is acute pain, pain more than 3 months is chronic pain, and pain in between is subacute pain.