An itch, also known as pruritus, is classified as a sensory stimulation to scratch a certain area of the skin. An itch can be a fleeting sensation, as with a random tickle or prick, or persistent, as with a rash such as eczema or other skin irritant such as an allergen. Itch has been demonstrated to be closely related to pain and to share many of its physiological mechanisms. The relationship between pain and itch is evident in the fact that itch sensations occur along a similar neurological and sensory pathway as sensations of pain, and the fact that individuals who are insensitive to pain are also insensitive to itch. Itch is induced by mechanical, chemical, thermal, or electrical stimuli of sensory receptors in the peripheral nervous system, or by psychological prompts. The receptors that are responsible for the sensation of itch caused by environmental stimuli are found within the upper layers of the skin. Once stimulated, usually by histamine within the body, a signal is sent through the peripheral nervous system to the brain (thalamus), where the information is processed and the command for the bodily response is issued. Itch can also originate as a result of damage to the nervous system (central or peripheral) or in response to the presence of excess opioids. Because of the scarcity of research available on mitempfindung, there is no widely accepted theory on how the referral of sensation is manifested. There are, however, a wide range of hypotheses which carry traction within the scientific community. One proposed mechanism implicates the nerve and its branches. At the cellular level, this hypothesis postulates that abnormal branching of neurons occurs during embryogenesis. During development, the branch of an afferent article may travel unusually far in the nervous system. Thus, in an individual with a fully developed nervous system, the stimulus at the end of one branch may be interpreted as coming from a point of ending in another, distant, part of the body. Again, research has not been done to prove this hypothesis as valid or invalid. There is an untested hypothesis that claims that<unk>  uses the spinocervical tract pathway. The cells in this tract lie in the dorsal horn of the spinal cord, and its axons run in the ipsilateral and dorsolateral quadrant, which is consistent with observations that stimuli in the trigger points are ipsilateral to the sites of<unk>  sensations. These axons project to the thalamus and midbrain, suggesting that the thalamus is involved in the phenomenon. The cells in this tract are also excited by mechanical stimuli, lending support that this pathway can explain the mechanism of<unk> . Central neuronal damage to this area – either direct or secondary to peripheral nerve damage – makes it an area of focal hyperexcitability or reduced inhibition. This hypothesis has been found to be unlikely because there would be an expected progression of itches (i.e., from legs to trunk, and from trunk to neck). However, there is no symmetrical distribution found between trigger zones and sites of<unk>  sensation. There is great support behind the idea of the thalamus affecting mitempfindung. Because of the arrangement of sensory regions in the thalamus, there may be a spread of excitation in this brain region. Studies have shown that the thalamic region dedicated to the trunk is found between the regions supporting sensation from the arms and legs. This supports the finding that trigger zones in the chest area lead to<unk>  sensation in the legs. And since the thalamic region for the face lies in a separate area called the arcuate nucleus, this explains why the face remains unaffected by<unk> . Some spread in association within the cerebral cortex may also explain the large distances between trigger points and<unk>  sensation sites. In the precentral area where the homunculus rests, it is known that hand and shoulder areas overlap the trunk area. And the area of the thumb overlaps that of the upper part of the tongue. There is a published case in which stimulation in the thumb led to a<unk>  sensation in the upper part of the tongue.
Referred itch
Pain out of proportion
Baricity
Referred pain
Coolie itch
Body odor
Ground itch
Grain itch