Pain is an unpleasant but very important biological signal for danger. Nociception is necessary for survival and maintaining the integrity of the organism in a potentially hostile environment. Pain is both a sensory experience and a perceptual metaphor for damage and it is activated by noxious stimuli that act on a complex pain sensory apparatus. However, chronic pain having no more a protective role can become a ruining disease itself, termed 'neuropathic pain'.