Pain is a complex sensation that is similar to a feeling. Pain is always subjective, cannot be measured, cannot be proven and cannot be refuted. Since the 1970s there has been an official definition of the International Association for the Study of Pain that does justice to acute and chronic pain as well as to the biopsychosocial model of disease.
“Pain is an unpleasant sensory and emotional experience associated with, or resembling that associated with actual or potential tissue damage.”
Definition by the International Association for the Study of Pain (IASP)
This model states that a disease, and thus also pain, is not always and exclusively caused by physical changes, but that dysfunction, emotional, psychological and social problems and disorders can also result in pain and diseases.