"Can skin itching be considered a form of pain?""What's your question?" Vincent Bailleul asks us on our Facebook page. This is our reader question of the week. Thank you all for your participation.
At first glance, itching and pain seem to belong to two distinct worlds: one would drive us to scratch frantically, the other to protect ourselves from a threat. Yet, when we explore the neural architecture that governs these sensations, the boundary blurs. Itching (or pruritus) actually mobilizes a network of neurons closely resembling that of pain.
A dedicated nerve pathway, but one closely related to that of pain
Itching originates from the stimulation of pruri-receptors, specialized nerve endings scattered throughout the skin. These receptors transmit the signal along a chain of three neurons: the first starts in the skin and travels up to the spinal cord; the second relays the information in the spinal cord; the third, finally, projects the signal to a brain area involved in sensations and emotions, where we become aware that "it itches".
This organization strongly resembles that used by pain, which is no coincidence: the two systems are closely linked, even if they rely on distinct fibers and receptors.
Scratching: a strange dialogue between pain and itching
If scratching provides relief, it's precisely because the itch itself isn't painful… but it can be masked by scratching. Our skin harbors a second type of receptor: nociceptors, which specialize in pain. When we scratch, we inflict a micro-aggression on our skin, intense enough to activate these nociceptors.
Upon reaching the spinal cord, pain signals inhibit itch signals: a kind of biological priority that explains the temporary relief. But the rebound effect is rapid, because the neurons involved have been overactivated… and the urge to scratch returns immediately!
Read alsoWhy You Shouldn't Scratch Yourself
Itching and pain, "cousins" in the sensory landscape
In neurobiology, itching is considered a distinct sensation, possessing its own receptors and activation pathways. It is therefore not pain, strictly speaking. However, the two sensations are so closely related, particularly through their mutual inhibition and their proximity in the spinal cord and brain, that they can be seen as "cousins" in the vast sensory landscape.
Perhaps the closest thing between itching and pain is the way they both prompt us to question our bodies: one calls for immediate protection, the other for a compulsive reaction. Two warning signals, each in its own way.
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