It feels *so*  sweet and relieving when you scratch that awful itch. Until it starts itching more and drives you crazy. Have you ever wondered why its like that?

An itch, also known as ‘Pruritus‘, is a general sensation arising from the irritation of skin cells or nerve cells associated with the skin. While it can be a nuisance, pruritus serves as an important sensory and self-protective mechanism, as do other skin sensations such as touch, pain, vibration, cold and heat. It can alert us to harmful external agents, but can become unbearable if not treated.

The research published in the journal Neuron states that the study conducted on mice provides insight into how to prevent itchy sensations in humans, especially those suffering from chronic itching. It is a well-known fact that scratching blocks the itching sensation. The pain that is accompanied by scratching manages to temporarily distract the brain from the itch. These pain signals are transmitted to the brain by nerve cells just like an itchy feeling is also transmitted by another set of nerve cells.

“The problem is that when the brain gets those pain signals, it responds by producing the neurotransmitter serotonin to help control that pain,” said senior author Zhou-Feng Chen in a statement. “But as serotonin spreads from the brain into the spinal cord, we found the chemical can ‘jump the tracks,’ moving from pain-sensing neurons to nerve cells that influence itch intensity.”

Pruritus is a dominant symptom of many skin diseases and also occurs in some diseases that affect the entire body. An itching sensation of the skin arises due to stimulation of pruriceptors—itch-sensing nerve endings—by mechanical, thermal or chemical mediators. These include:

  • Chemicals for immune response (histamines) and pain relief (opiods)
  • Neuropeptides, which include pain-regulating messengers released within the brain, such as endorphins
  • The neurotransmitters acetylcholine and serotonin
  • Prostaglandins, which are lipids that, among other functions, create the sensation of pain in spinal nerve cells

Stimulation by any of these agents is typically related to inflammation, dryness or other damage to the skin, mucous membranes or conjunctiva of the eye.

In general, pruritus involves activation of the pruriceptors of specialized nerve cells called C-fibers. These C-fibers are identical to those associated with the sensation of pain, but they are functionally distinct and only convey the itch sensation—they comprise about 5 percent of the total C-fibers in human skin. When stimulated superficially on the skin, these C-fibers carry signals along the nerve to the spinal cord and on to the brain, where they are processed, generating a scratching or rubbing reflex response. Scratching and rubbing then interfere with the sensations arising from pruriceptors by stimulating various pain and touch receptors in the same areas. Scratching can relieve itch by creating minor pain. But when the body responds to pain signals, that response actually can make itching worse. Though it is helpful in relieving the itch, scratching offers only temporary relief and may cause the skin to become further irritated and possibly tear, which could result in an infection. Scratching may seem to relieve an itch, but it actually makes it worse.

Despite approximately a century of pruritus research, there is no single effective antipruritic treatment, but several topical and orally-administered agents are available that suppress itching in certain clinical settings. These agents include lotions and creams (such as calamine and hydrocortisone), antihistamines, opioid antagonists, aspirin and ultraviolet light therapy.


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