What is Itch and Scratching?

What is Itch and Scratching?

Itch is a sensation that many people experience yet don’t understand. The philosopher Aristotle (384-322 BC) recorded one of the first known descriptions of itch, characterizing how animals scratch themselves in a manner similar to modern humans. Since then, it has been a topic of interest for physicians and philosophers alike. In 1660, one of the earliest formal definitions of itch was coined by the German physician Samuel Haffenreffer, where he described itch as ‘‘an uncomfortable sensation that provokes a desire to scratch.’’

Evolutionarily, itch is an important adaptation that alerts us to potentially hazardous situations. Our bodies are wired to recognize hazardous contact with irritants like stinging nettles and poisonous insects. In addition to its protective role, itch has also been important for aiding in the healing process by alerting the body of disruptions in the skin barrier, whether it be through infection, injury, or trauma.

Itch, in and of itself, is a subjective experience and can’t be measured. However, since it is a sensation, itch also triggers a reflex. A reflex is an unconscious response to a stimulus, essentially your body’s way of instantly reacting without thought or decision-making processes. When you touch a hot surface or prick yourself with a needle, the withdrawal reaction happens almost immediately — that’s due to special nerve pathways in our bodies designed for quick responses like these called reflex arcs. When a stimulus occurs, it activates receptors to send signals to your spinal cord. From there, commands are conveyed to a target organ or muscle group, bypassing the brain. Reflexes are responsible for your urge to scratch or rub when you feel the sensation of itch.

In general, sensation is mediated by the nervous system, which consists of the brain, spinal cord, and nerve fibers that connect to your other organs. The nervous system receives information from the sensory nerves that supply your tissues like the skin and sends signals to the spinal cord and brain, where that information is interpreted as a particular sensation such as itch, pain, or even cold or heat. Hence, sensation cannot be registered in your mind without reaching your brain. Your brain is ultimately where you perceive the itch, independently of the reflex or whether you scratch. This is why it’s a virtual paradox to tell someone, “Just stop scratching!”. It’s impossible to fully suppress scratching because any moment you are not thinking of it, you will find yourself scratching.

The sensation of itch historically was thought to be a submodality of pain. Thus, although significant resources have been dedicated to understanding the basic mechanisms underlying pain, itch has been relatively overlooked. Itch and pain are closely related, but distinct sensations. While they share many overlapping mediators and receptors, recent research has uncovered the existence of itch-specific nerves.

However, since itch is a reflex, in addition to being a sensation, you would still feel itch in your spinal cord, even if your brain was missing. As a result of its ability to evoke a reflex, we have ways to measure itch objectively through scratching. For instance, we could count the number of times you scratch in a given period of time or measure the amount of time you spent scratching. These methods are still indirect, but we could also ask about how you are feeling and experiencing itch subjectively.

Overall, itch is a complex experience that affects us both physically and psychologically. Though itch has served a protective evolutionary role, in modern day, it is an uncomfortable and for some, unbearable experience that affects people of all ages with little useful purpose. While itch in and of itself is not harmful, chronic itch can significantly impact your quality of life. As we gain further understanding into the mechanisms underlying itch in both normal and pathological conditions, we may better develop new targeted treatments to add to our arsenal of effective therapies to combat chronic itch.