Early humans explained the mystery of pain by associating it with evil, magic, and demons. Relief was the responsibility of sorcerers, shamans, priests, and priestesses, who treated their clients with herbs and rituals.
On stone tablets, ancient civilizations recorded accounts of pain and the treatments used, including pressure, heat, water, and sun. The Greeks and Romans were the first to advance a theory of sensation, the idea that the brain and nervous system were involved in the perception of pain. During the Middle Ages and into the Renaissance, evidence began to accumulate supporting these theories. Leonardo da Vinci and his contemporaries came to see the brain as the central organ responsible for sensation, with the spinal cord transmitting sensations to the brain.
In the 19th century, pain came to dwell under a new domain—science—which paved the way for advances in pain therapy. Physician-scientists discovered that opium, morphine, codeine, and cocaine could be used to treat pain. In the late 1800s, research led to the development of aspirin, to this day the most commonly-used pain reliever. Before long, anesthesia—both general and regional—was refined and applied during surgery.
Pain is defined as an unpleasant sensory and emotional experience associated with actual or potential tissue damage. There are two basic categories of pain, acute and chronic, and they differ greatly.
Acute pain usually results from disease, inflammation, or injury to tissues. This type of pain generally comes on suddenly—for example, after trauma or surgery—and may be accompanied by anxiety or emotional distress. The cause of acute pain can generally be diagnosed and treated, and the pain is self-limiting—confined to a given period of time and severity. In some instances, it can become chronic.
Chronic pain is widely believed to represent a disease in and of itself. It persists over a longer period of time than acute pain and is resistant to most medical treatments. Chronic pain often persists longer than three months, or longer than expected for normal healing. It can be made much worse by environmental and psychological factors. It can—and often does—cause severe problems for patients, as pain signals keep firing in the nervous system for weeks, months, or years. There may have been an initial mishap such as a sprained back or serious infection, or there may be an ongoing cause of pain such as arthritis, cancer, or infection. However, some people suffer chronic pain in the absence of any past injury or evidence of illness.