NGF is known to up-regulate neuropeptides, especially substance P. Substance P has been found to have an important role in inducing pain; however, there is no confirmation that substance P directly causes acute sensitization. Instead, substance P may contribute to itch by increasing neuronal sensitization and may affect release of mast cells, which contain many granules rich in histamine, during long-term interaction. Central sensitization
Noxious input to the spinal cord is known to produce central sensitization, which consists of allodynia, exaggeration of pain, and punctuate hyperalgesia, extreme sensitivity to pain. Two types of mechanical hyperalgesia can occur: 1) touch that is normally painless in the uninjured surroundings of a cut or tear can trigger painful sensations (touch-evoked hyperalgesia), and 2) a slightly painful pin prick stimulation is perceived as more painful around a focused area of inflammation (punctuate hyperalgesia). Touch-evoked hyperalgesia requires continuous firing of primary afferent nociceptors, and punctuate hyperalgesia does not require continuous firing which means it can persist for hours after a trauma and can be stronger than normally experienced. In addition, it was found that patients with neuropathic pain, histamine ionophoresis resulted in a sensation of burning pain rather than itch, which would be induced in normal healthy patients. This shows that there is spinal hypersensitivity to C-fiber input in chronic pain. Treatment
A variety of over-the-counter and prescription anti-itch drugs are available. Some plant products have been found to be effective anti-pruritics, others not. Non-chemical remedies include cooling, warming, soft stimulation.
Topical antipruritics in the form of creams and sprays are often available over-the-counter. Oral anti-itch drugs also exist and are usually prescription drugs. The active ingredients usually belong to the following classes:

Antihistamines, such as diphenhydramine (Benadryl)
Corticosteroids, such as hydrocortisone topical cream; see topical steroid
Counterirritants, such as mint oil, menthol, or camphor
Crotamiton (trade name Eurax) is an antipruritic agent available as a cream or lotion, often used to treat scabies. Its mechanism of action remains unknown. Local anesthetics, such as benzocaine topical cream (Lanacane)Phototherapy is helpful for severe itching, especially if caused by kidney failure. The common type of light used is UVB.Sometimes scratching relieves isolated itches, hence the existence of devices such as the back scratcher. Often, however, scratching only offers temporary relief and can intensify itching, even causing further damage to the skin, dubbed the "itch-scratch cycle".The mainstay of therapy for dry skin is maintaining adequate skin moisture and topical emollients. No studies have been conducted to investigate the effectiveness of emollient creams, cooling lotions, topical corticosteroids, topical antidepressants, systemic antihistamines, systemic antidepressants, systemic anticonvulsants, and phototherapy on chronic itchiness of unknown origin. The effectiveness of therapeutic options for people who are terminally ill with malignant cancer is not known. History
In 1660, German physician Samuel Hafenreffer introduced the definition of pruritus (itch). Epidemiology
Approximately 280 million people globally, 4% of the population, have difficulty with itchiness. This is comparable to the 2–3% of the population who have psoriasis. See also
Feeling, a perceptual state of conscious experience.