Library · Physiology
Itching
Make it clearer
Itching has a medical name, pruritus. It starts in the skin, where sensory nerve fibers pick up a stimulus and alert the nervous system, and that alarm is what we feel as the urge to scratch.
The first neuron identified as responsible was the unmyelinated C fiber: unmyelinated because it lacks the myelin sheath that wraps other nerves and makes them fast, so this one conducts slowly. That fiber depends on histamine, the substance behind allergic reactions. Histamine docks onto a receptor called H1 on those same nerve endings, and that is where itching and pain come from.
But that is not the whole story, and it explains something many people have experienced. There are other neurons, the non-histaminergic ones, that also produce itching by separate routes. When the itch travels that way, an antihistamine, which is built to block histamine, will probably not take it away, and that does not mean the person is taking it wrong.
In brief
Itching, or pruritus, begins when sensory nerve fibers in the skin pick up a stimulus.
The first neuron identified was the unmyelinated C fiber, slow and histamine-dependent.
Histamine, the same one behind allergic reactions, acts on those endings through its H1 receptor, and that produces itching and pain.
There are also non-histaminergic neurons, which probably explains itching that antihistamines do not relieve.
Itching does not travel down a single wire, so shutting one off does not always shut it off.
Sources (2)
- National Center for Biotechnology Information, StatPearls PublishingUremic Pruritus Evaluation and Treatment, StatPearlsPublished
- National Center for Biotechnology Information, StatPearls PublishingBiochemistry, Histamine, StatPearlsPublished
This page explains the topic in general terms; it does not tell anyone what treatment to follow.
Updated