Pain is a sensory symptom of tissue damage or disorder that can either be acute or chronic. Researchers have learned a great deal about pain and its physiological and psychological basis, leading to pain management treatments that can provide complete or partial pain relief. Untreated pain can interfere with the healing process by affecting the immune system. In cases of back pain, discomfort can impede the rehabilitation process by interfering with exercise and increasing psychological distress. Chronic back pain tends to be very difficult to treat, especially in cases involving failed back surgery or nerve pain. Pain is inherently subjective, and a greater awareness of the need for taking pain seriously is growing among the health community as well as the public.