Adventures in Ethics and Science

The other day, my better half and I were discussing scratching. Predictably, in the course of the discussion, I became aware of every itchy square millimeter of skin I might possibly possess.

I wondered whether scratching actually works — that is, whether scratching ever acts to make an itch go away, or even to reduce it.

“Of course it does,” my better half opined. “Why else would we do it?”

“Because we’re poorly adapted?” I ventured.

So, here’s the question*:

Is there any good research to demonstrate whether scratching alleviates itching? Is there any evidence (beyond your mom’s say-so) that scratching is bound to exacerbate your itching? Is there a “right” way to scratch that makes a difference here.

Sheesh, just writing this post makes me feel like I need an oatmeal bath!

______
*Yeah, actually three questions, but they’re related.

Comments

  1. #1 Raúl
    October 28, 2008

    I think it does. We are not the only species that scratches. Dogs with fleas do it all the time. If it didn’t help any, why would other species do it?

  2. #2 cephyn
    October 28, 2008

    depends on the reason for the itch.

  3. #3 Becca
    October 28, 2008

    Emperically, it results in subjective alleviation. It distracts you from the itch.
    And while there are many obvious itches one shouldn’t scratch (posion ivy, mosquito bites, ect. are definitely exacerbated by scratching), I don’t think “normal” itches are exacerbated by scratching. I suppose if you scratch really hard (to the point it gets extra pinkish) you’re probably increasing blood flow and maybe you could get a very minor tissue damage inflammatory response.

  4. #4 PalMD
    October 28, 2008

    There are a number of conditions in which scratching actively exacerbates itching. For example, people with dermatographism have mast cells that are particularly susceptible to physical trauma, and scratching causes mast cell degranulation, leading to a weal and flare response.

    that is, you can write your name on their skin with your finger nail, and you’ll get nice raised red itchy letters on the skin.

  5. #5 Liz
    October 28, 2008

    It won’t really answer your questions, but Atul Gawande’s New Yorker article “The Itch” is worth a read.

  6. #6 Rosie Redfield
    October 28, 2008

    I think we can all agree that scratching feels good while it’s in progress, and I think I’ve read neurological explanations for this. The big issue is whether the itching is reduced (or increased!) once the scratching stops.

  7. #7 Comrade PhysioProf
    October 28, 2008

    SG, I sure don’t know. But now I am all fucking itchy, and it’s all your motherfucking FAULT!!!!!!!1!1!!!

  8. #8 Eva
    October 28, 2008

    There’s this idea: “It is proposed that stimulation of large areas of skin such as by scratching, generates inhibitory activity which suppresses itch excitation.”

  9. #9 Chris
    October 28, 2008

    Scratching makes a lot of sense. Our first indication that a bug has landed on us is often an itching sensation at that spot. Thus, by scratching, we often knock the critter off before it has a chance to bite us. This makes a lot of sense as an evolutionary mechanism, because we know that insects can transmit all sorts of nasty diseases like malaria, dengue fever, etc.

    The fact that our system sends a lot of false positive signals to the brain is just indicative of a “better safe than sorry” strategy.

  10. #10 Corey
    October 28, 2008

    As I recall, the sensation of itching is due to low level firing of pain receptors. Much like a sharp pain nearby reduces pain through signal buffering (I can’t recall the exact mechanism at the moment), I would think scratching alleviates the itching in a similar manner.

    So…it alleviates the sensation, not the cause…

  11. #11 Comrade PhysioProf
    October 28, 2008

    Oh, shit, I thought this was obvious. The adaptive benefit of itching and scratching is thought to be removal of parasites and bloodsucking predators from our skin.

  12. #12 PalMD
    October 28, 2008

    @Corey

    Specific “itch” receptors, separate from pain receptors, have been identified (e.g. http://www.jneurosci.org/cgi/content/abstract/17/20/8003)

  13. #13 Corey
    October 29, 2008

    *looks at PalMD’s comment*

    *sighs*

    *edits his physiological psychology lectures*

    So much for my old physio psych books ;)

    Anyways, it’s still possible that mechanical activation of other receptors might be the source of alleviation of the symptoms of itching.

  14. #14 Mark P
    October 31, 2008

    IBS: Itchy Back Syndrome.

    As you get older you will almost certainly find that there is a point on your back that you absolutely cannot reach that will itch constantly. I remember seeing my father rubbing his back against a door frame as he talked to me. Now I have that same itch. It’s IBS.

    I always naively thought that scratching alleviated itching because it “overloaded” the nerves. In some cases it seems to eliminate the itch, but in other cases the relief is temporary. I have found that running very hot water over poison ivy alleviates the itch for a significant time, and there seems to be no rebound or other ill effects.

    But scratching does not relieve IBS, except for a moment. The only way to deal with it is to do something else to get your mind off it.

  15. #15 Quercki M. Singer
    November 13, 2008

    PalMD wrote:
    that is, you can write your name on their skin with your finger nail, and you’ll get nice raised red itchy letters on the skin.

    I’ve got dermatographism, and it isn’t particularly itchy. IBS is much worse.

    Once I demonstrated it for an acquaintance by letting him “write” on my tummy. He said, “This is even more fun than writing in wet concrete!”

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