Wondering why your itch needs scratching?

Mark Andrews at Lake Erie College of Osteopathic Medicine states the following:

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.

That is from an article at Scientific American, full link here