This weekend I went on a two-day camping trip which afforded me the opportunity to imagine the environment in which our species evolved. And to do a bunch of bitching and whining about all the minor discomforts I experienced in that environment. And that led me to some speculations about whether the extremely comfortable nature of our modern life is capable of disregulating a pain system that was designed to work in a far different world.
The modern world is soft
Our ancestors evolved in an environment without soft beds, couches, pillows, chairs, floors, and roofs. Their world was composed solely of hard jagged things, dirt and pathogens, and scratchy stuff. When they were sleeping, sitting, standing or walking, they would have been in constant contact with objects that are hard and rough, and often cold, hot, wet, dirty or infested with bugs. This makes a startling contrast with our modern world, which is highly engineered to ensure that every object we touch is soft and smooth.
And this difference became very noticeable to me after a day or two of camping, even though I brought sunscreen, bug spray, clothes from REI, a sleeping bag, pillows and an inflatable bed. So I was not exactly roughing it, but my experience was still far rougher than my modern life. I had bug bites, I was covered with a layer of sweat and dirt, I had scratches from branches while hiking. I know, its heartbreaking, but I made it through.
As I was summoning the inner strength to perservere, it occurred to me that this constant low grade non-injurious irritation to the skin is actually the natural condition for humans. Which made me wonder whether the complete absence of this stimulus in the modern world can somehow dysregulate the pain system. Part of what gave me this idea was a seemingly related idea called the hygiene hypothesis.
The modern world is sterile
The hygiene hypothesis essentially asks whether the unnaturally clean lifestyles of the modern world are causing problems with our immune systems, which were designed to work in a world full of constant exposure to pathogens.
The immune system is basically an army of cells designed to kill invaders. In order to function optimally it needs proper training at a young age in the form of exposure to invaders. If it is denied this practice, it will lack essential skills, such as knowing what to attack when and how much. And perhaps if the army has nothing to do because there are no invading armies to fight, it gets restless and overreacts to the presence of minor irritants, which causes allergies. Or maybe it just gets confused and starts attacking the body, causing autoimmune disease. This is a rough sketch of some very complex ideas, but the logic is simple – the immune system is a complex system which evolved in the presence of constant exposure to pathogens, and therefore removal of this key input into the system can be expected to change its behavior in some way.
The hygiene hypothesis appears to be gaining more and more scientific support, including epidemiological data which shows various allergic and autoimmune diseases are far more common in sterile environments than more natural environments which involve far more exposure to pathogens.
The comfort hypothesis
So if the hygiene hypothesis can explain the modern rise in allergies, autoimmune disease, and the fact that my daughter cannot take peanuts to school, can the “comfort hypothesis” explain the prevalence of chronic pain in our society?
There is some similarity in logic between the two ideas. The pain alarm system is part of the immune system. It evolved in a situation in which one of the major players, the skin, was constantly receiving minor amounts of nociceptive input. We know that nociceptive or other sensory input in one area of the body will affect pain levels in other parts of the body. And counterirritation is a technique for pain relief that involves using an externally applied substance, such as capsaicin, to causes irritation and mild inflammation of the skin, for the purpose of relieving pain in other areas, such as muscles or joints.
Is it possible that a radical reduction in the amount of this peripheral low level nociceptive input to the skin can somehow cause disregulation of the pain alarm system, perhaps causing it to focus excess attention inappropriately in other areas? Perhaps this is a contributing factor (not the sole factor of course) in conditions such as allodynia, complex regional pain syndrome or fibromyalgia. Or perhaps it is involved in other more common forms of chronic pain such as low back pain or joint pain.
I don’t know the answers to these questions and I do not have any real practical recommendations on the basis of my speculations. Except that it’s probably a good idea to “rough” it from time to time so as not to become too “soft.” Our perceptions are in many ways relative. Food tastes better when you fast for a while. And my bed feels a lot softer after a camping trip.
What do you think about these ideas? Have you heard someone else propose them in a different form? Let me know in the comments.