What is pain? It might seem like a simple question, but it is not.
The International Association for the Study of Pain (The International Association for the Study of Pain - IASP), defines pain as "An unpleasant sensory and emotional experience associated with, or similar to, actual or potential tissue damage", with sensory, emotional, cognitive and social components.
When we talk about real damage we refer to a concrete damage (a wound, a burn ...). When we talk instead of potential damage we can think of what happens to a hand that comes close to a very hot object: when we have the perception of heat, which could potentially cause an injury, we are led by our brain to withdraw it, to protect us.
Scholars reasonably agree that pain is an unwelcome sensation, which makes us want to stop and change our behavior..
Currently we no longer think of pain as a measure of tissue injury. We have known for at least twenty years that there is no strict correlation between the tissue damage found in radiological examinations and the clinical presentation: X-rays may show tissue damage without pain, just as a completely normal X-ray may belong to a patient with severe pain.
Nowadays pain is considered as a complex and highly sophisticated protection mechanism.
Pain is not just a physical sensation. It is conditioned by attitudes, beliefs, personalities, social factors and can influence emotional and mental well-being.
 The International Association for the Study of Pain (IASP) is an international company that promotes research, education, and policies for the understanding, prevention and treatment of pain. The IASP was founded in 1973 under the leadership of John J. Bonica (anesthetist, known as the founding father of the discipline of pain medicine). Publishes the scientific journals PAIN, PAIN Reports, and PAIN: Clinical Updates. The IASP currently has more than 7.200 members from 133 countries and 94 chapters around the world. www.iasp-pain.org
Lorimer Moseley, Explainer: what is pain and what is happening when we feel it? " www.theconversation.com, November 18, 2015
 Culvenor A, Claus A, The disconnect between tissue pathology, load and pain: implications for clinicians, www.bodyinmind.org