let’s get receptive: the relationship between pain and itching

black and brown coat animal on brown trunk
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When I was still in my physical therapy graduate program, we had a lecture on pain and neural pathways, and I stayed after class to ask the professor about the relationship between pain and itching because I noticed my itches sometimes felt like they traveled along a nerve (such a perk of being a PT student, you’ve got to know your nerve branchings!).

I’m reading this book now called Living with Itch by doctors Gil Yosipovitch and Shawn G. Kwatra. This book first got on my radar when I was reading a National Eczema Association post called “Itching for Answers”, and it mentioned Dr. Yosipovitch and talked about how cytokines (one of the molecules secreted by the body’s immune cells that we usually blame for our overactive immune responses), are also located in the nerve cells. The thought is that some of the nerves may have “faulty wiring” and so they are constantly firing and sending up itch signals when there is low to no itchy stimuli.

Anyway, the book goes into detail about various chronic itch-related disorders/diseases as well as the anatomy behind the itch, and it depicts the relationship of pain and itching to be almost inverse. As the book explains, we have a bunch of different sensory receptors on our external body to send information from what we encounter in our environment to our brain. One such receptor type, located in the epidermis layer (the shallow most skin layer) is the C nerve fiber, which relays information about, you got it, pain and itching. These C nerve fibers send the sensation information to a structure called the dorsal root ganglion, and then the info crosses the spinal cord and goes up the opposite side of the lateral spinothalamic tract to get to the thalamus in the brain. There the thalamus sends info about the itch sensation to other parts of the body that link it to our physical, cognitive, and emotional responses. The lateral spinothalamic tract also relays information about pain and temperature, which is important and I’ll get to in a minute.

So what do we know about pain and itching? We know our bodies’ physical response to pain versus itch is very different. With pain, we withdrawal the part of the body that comes in contact with the painful stimuli; step on a nail, you immediately try to pull your foot away. But with an itch, we immediately go to a scratch reflex. The book goes into more detail about why that is, saying that the scratch reflex causes a sort of pain, which effectively masks the itch, and we now know that is precisely because the two stimuli types do share that same lateral spinothalamic tract. And because temperature also can share that tract, this is why using cold on inflamed skin, or taking a hot bath can also mute the itch.

Lastly the book goes into why chronic pain and chronic itch can be similar. The biggest commonality is that both involve the nerve fibers being overactive, so we perceive the pain/itch to be even more intense (this is called hyper sensitization). And yes, when the sensations are that heightened, like say you are always itchy due to eczema or another condition, something that should be painful like an electric shock, or pouring rubbing alcohol on your scratch wounds (the latter which I’ve done…) might just make you itch more!

The most recent medications/treatments on the market are called biologics (and include names such as Dupixent), and they target the cytokines that give us so much grief. For eczema, those cytokines include interleukins 4 and 13 (IL-4 and IL-13) so far, and they are working to make treatments that target more ILs in the future.

One other takeaway from the book that I thought was relevant is that the epidermis layer, when sufficiently compromised (like after it’s been scratched a lot), can have more sensitive nerve fibers because they are more exposed by the broken skin barrier. So one important treatment in managing eczema is helping to try to repair and protect the skin barrier to subsequently protect the nerve fibers. The book mentions two ways of going about this:

  1. using moisturizers with ceramide in them to help coat the skin barrier as the skin barrier lacks the protein filaggrin*
  2. using moisturizers and cleansers that are more acidic so that they help get the skin back to its normal pH range of about 4-6 (with 1-6 being acidic, 7 being neutral, and 8-14 being alkaline). Note that most soap bars are alkaline.

*A cool way to know if you genetically are lacking filaggrin is to look at your palms. People with crazy amounts of lines are generally lacking filaggrin. I’ll be talking more about filaggrin in a post later this week. Meanwhile look at my lack of filaggrin below!

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What I am curious about is why then, is it advised by so many dermatologists to take bleach baths? I understand that when diluted, bleach can still help kill a lot of germs on the skin, but if bleach is a pH level around 12 (so pretty basic/alkaline and maybe gets diluted to around 9 when in a bath), it is very far from the desired pH of our skin. If we are adding an element that further changes our skin pH, how does that help our healing? Though I guess if the pH of our skin is higher than 9, bringing it down to 9 with bleach baths would be beneficial then too.

I haven’t searched super thoroughly yet, but the most recent study I found so far indicated that bleach baths with a course of topical steroids was no more effective than just doing the course of topical steroids alone. A review tested a treatment group using bleach baths and mupirocin (a topical antibiotic) versus a control group using normal baths and petroleum jelly and found that the former was more effective, at one month at reducing Staphylococcus aureus (the bad Staph we all know), but again this is not comparing bleach baths in isolation (and the study went on to say that at 3 months there was unchanged frequency of Staph in the treatment group meaning it was still as widespread on the body, though they didn’t test the concentration to see if the quantity of Staph had changed).

Yet another study supported that the topical antibiotics with diluted bleach baths were most efficient at killing Staph, yet also noted all groups (no bleach, bleach with topical antibiotics, etc) had reoccurrence rates of Staph after 4 months. A different review on using diluted bleach talked about how bleach is awesome because it’s a ubiquitous cheap house product that kills bacteria, viruses, and fungi alike and doesn’t cause bacteria to become resistant. However, then it also talks about why the studies using it for infected eczema are lacking, and includes reasons that one might one to avoid using it such as:

  • the amount in a cleaner can vary
  • its strength can degrade over time
  • it can make dermatitis worse
  • it often contains fragrances
  • the studies done didn’t have enough people in them, and
  • there is no consensus on the optimal amount of bleach to use or how frequently use it to effectively stave off future Staph infections.

And again, I’m not sure what the role of a diluted bleach bath would be for those of us avoiding topical steroids/going through withdrawal and not currently on antibiotics.
However, given the pH of bleach alone, and then adding the fact that so many studies mentioned the frequency of Staph reoccurrence, as my skin is going okay right now, I’ll personally be using apple cider vinegar baths more frequently instead.

Amended: This does not mean I no longer take bleach baths, because I still do. I just treat them as a more aggressive maintenance treatment for the management of my skin, and subsequently take them sparingly, but as needed.

 

REFERENCES

Barnes TM, Greive KA. Use of bleach baths for the treatment of infected atopic eczema. Australasian Journal of Dermatology. 2013 Nov; 54(4): 251-258.

Chang MW, Hirschmann JV. Bleach Baths for Atopic Dermatitis. NEJM Journal Watch Dermatology. 2009 Jun 5;(nd).

Crane, Margaret. “Itching for Answers.” National Eczema Association, https://nationaleczema.org/itching-for-answers/. Accessed 23 Oct 2018.

Fritz SA, Camins BC, Eisenstein KA, Fritz JM, Epplin EK, Burnham C Dukes J, Storch GA. Effectiveness of Measures to Eradicate Staphylococcus aureus Carriage in Patients with Community-Associated Skin and Soft Tissue Infections: A Randomized Trial. Infect Control Hosp Epidemiol. 2011 Sep; 32(9): 872-880.

Gonzalez ME, Schaffer JV, Orlow SJ, Gao Z, Li H, Alekseyenko AV, Blaser MJ. Cutaneous microbiome effets of fluticasone proprionate cream and adjunctive bleach baths in childhood atopic dermatitis. J Am Acad Dermatol. 2016 Sep; 75(3): 481-493.e8.

Panther DJ, Jacob SE. The Importance of Acidifucation on Atopic Eczema: An Underexplored Avenue for Treatment. J Clin Med. 2015 May; 4(4):970-978.