The neuroscience behind an itch
Written by Elijah Lagman, Year 13
“There is pleasure when an itch is scratched. But to be without an itch is more pleasurable still.” – Nāgārjuna, Buddhist philosopher
Let’s put the question out there: Why do we itch? Well, I can confidently tell you it’s because that part of your body is itchy… but you already knew that, didn’t you?
Recent research has tried to more adequately explain this mystery. The National Institute of Dental and Craniofacial Research reported that a molecule known as neuropeptide natriuretic polypeptide b (Nppb) is released from specific nerve cells in the skin, and is responsible for the itching sensations we feel. The molecule is actually released quite far from the actual itch site, but it triggers an electrochemical cascade that ultimately tempts the brain to scratch the “itchy” area.
A class of nerve cells known as TRPV1-expressing neurons are responsible for pain, itch and heat. This was proven in 2013, when neuroscientists Hoon and Mishra genetically engineered mice born without these neurons, and the mice could not feel such sensations. Now, although this experiment is quite ethically questionable, I still think it’s scientifically sound! After all, imagine a cold-blooded mouse; this mouse would probably die immediately if released in the wild. Now that’s a perfect example of how natural selection works.
But I digress. Let’s continue.
Hoon and Mishra also found that a specific subset of these TRPV cells that sense itchiness produce Nppb, unlike their pain-sensing cousins. So if you stimulate the skin with, let’s say, a strand of hair, or maybe even slowly stroke it with a feather, a signal is sent across sensory neurons to the brain through the release of these Nppb molecules. Because of this, Hoon and Mishra followed up their cold-blooded mouse experiment, and engineered mice that specifically lacked the variation of the TPPV1 neuron responsible for sending itches. The results--if you haven’t already guessed--were mice that sensed heat and pain, but not itches.
However, although we were able to find a neural explanation for why we itch, other questions have also arisen, such as ‘why does scratching the itch make it go away?’ Sadly, the answers to these questions remain undiscovered.
The sense of pain and itch is different. This leads to some ethical considerations. Torture is highly associated with pain and one can sufficiently argue that a douse of urushiol (drop from poison ivy) can make a person do some serious self-harm—so don’t get any ideas.
Anyway, here’s my two cents: When you get an itch, don’t scratch it unless you’re a masochist.
Works cited:
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