Pain is an unpleasant feeling which may be associated with actual or potential tissue damage and which may have physical and emotional components. According to the International Association for the Study of Pain (IASP), one should distinguish between pain and nociception.The word "pain" comes from the Latin: poena meaning punishment, a fine, a penalty.
The term "pain" is a subjective experience that typically accompanies nociception, but can also arise without any stimulus, and thus includes the emotional response. Nociception, on the other hand, is a neurophysiological term and denotes specific activity in nerve pathways. It is the transmission mechanism for physiological pain, and does not describe psychological pain. These pathways transmit the nominally "painful" signals, though they are not always perceived as painful. Although pain can be associated with tissue damage or inflammation, this is often not the case.
Despite its causing suffering, pain is a critical component of the body's defense system. It is part of a rapid warning relay instructing the central nervous system to initiate motor neurons in order to minimize detected physical harm. Lack of the ability to experience pain, as in the rare condition Congenital insensitivity to pain or Congenital Analgesia, can cause various health problems.
The two most common forms of pain reported in the U.S. are headache and back pain. Pain is also a term specifically used to denote a painful uterine contraction occurring in childbirth.