I was studying the skin, the microbiome and their interrelationships, and something really unexpected happened. I realized that Charles Darwin’s theory of evolution was incomplete. Even more unexpected were the repercussions this held for how I viewed skin, beauty, and whole-body care.
For decades, there has been a relatively silent, science-driven movement questioning Darwin’s theory of evolution allowing a new, more inclusive theory to emerge. As it stands, Darwin’s theory does not fully embrace environmental, micro, or macro influences on a species’ evolution or the interdependence of these factors outside of competition. With all the past and emerging science on the human microbiome, it’s becoming clear to the scientific community that humans, or any species for that matter, did not evolve in vacuums. In fact, we may not have been solely responsible for our own evolution. As humans, we had a counterpart throughout that process called the microbiome—a living layer that cloaks our bodies inside and out, comprised of trillions of microorganisms.
If you’re wondering what this has to do with your skincare routine, buckle up. The importance of the human-microbiome relationship could make you think twice about what you apply to your skin and perhaps even your overall diet and lifestyle. After all, you are more microbial than you are human and acknowledging that in your routine could be the shift your body needs.
Are We Outnumbered?
So just how much of you is microbial?
A number of scientists describe different ratios of human cells (HCs) to non-human cells (NHCs) like bacteria, fungi and viruses that we walk around with. Most current is the prestigious journal Nature suggesting the quantity of NHCs (39 trillion) to HCs (30 trillion).
While from the surface this partnership looks like a (still remarkable) approximate 4:3 match, a deeper look at the human versus microbial genetic codes paints an even more dramatic picture.
You see, within each of these NHCs, there resides a much vaster bank account of genetic information. In September 2017, researchers at Harvard and the University of Maryland published a seminal study in Nature “revealing millions of previously unknown genes from microbial communities in the human gut, skin, mouth, and vaginal microbiome”.
Twenty thousand human genes suddenly were matched against an astoundingly greater number—
33 million non-human genes.
Simple math confirmed that for every expressive human gene, there are somewhere in the neighborhood of 1,650 non-human genes. So, in the race for real dominance of evolutionary destiny, the scale appeared to look more like a true landslide in favor of the NHCs.
The last time I remembered even remotely feeling something like this was when I was seven years old and visiting the Hayden Planetarium in New York City for the first time. The presenter expanded the power of the animated telescope and the vision of the sky turned from a few planets and one star into hundreds, billions and then trillions of stars. Now, more than ever, I realize the same is true when we look within. We are more than meets the eye, we are truly a universe of life.
The Hologenome Theory
I’m not alone in this revelation. In fact, decades of science has led to an entirely new proposed theory of evolution that embraces this concept—"the hologenome theory”. Its namesake is based on the acknowledgement of the whole, or ‘holo’, of our microbial and human DNA, or ‘genome’, as a collective community, or ‘hologenome’.
A much more inclusive iteration of evolution, research supporting the hologenome theory was popularized as early as 1991 and has built momentum through the proceeding decades.
The evolutionary theorist, Lynn Margulis, first gained traction in 1991 in the book Symbiosis as a Source of Evolutionary Innovation when she identified the combination of different species as a ‘holobiont’.
A holobiont is an ecological unit that comprises all parts of a symbiotic relationship—in our case as humans, that would be our human cells and the thousands of species that define our microbiomes. As we discussed above, the genetic knowledge of the holobiont is referred to as the ‘hologenome’.
Margulis’s revelatory seed was expanded upon by recent research published in Microbiome Journal that proposed the hologenome as a viable unit of evolution.
The hologenome theory can be summarized simply as we are not evolving alone—our microbiome acts as our co-pilot in this process and, in many ways, is just as much a part of us as our human cells. We are part of a vast interdependent network featuring nature’s kingdoms and the environment, all connecting, communicating, competing, and cooperating with each other for resources, survival, longevity and legacy. As Mark Lyte, from Texas Tech University Health Sciences Center wrote ‘‘they monitor us’’ and ‘‘we monitor them’’ in a divine dance of “interkingdom signaling”.
What Does This Mean For Skin & Body Care?
This theory reminds us to zoom out of hyper-focus and view our bodies, nature’s kingdoms, and the environment as one integrated system.
Given all the wisdom that resides in the microbiome, it’s cataclysmic to the behavior of your skin and body to stress or strip yourself of this critical living layer. Yet we do it regularly. Harsh skincare products, unhealthy lifestyles, pollution, and especially mental stress take their toll on our skin and microbiome. Taking it one step further, your skin and microbiome are inextricably linked with nature, and changes in the environment like the climate crisis, UV radiation, and pollution can elicit a chemical stress response in the skin which generates a variety of mood-shifting hormones and neurotransmitters. These shifts can block the crosstalk between your skin and microbiome, dulling the skin’s intrinsic barrier function and rejuvenating abilities.
A well-balanced microbiome acts as a living communication network, helping direct your body with the wisdom its gained throughout your evolution. It speaks volumes to receptive human cells, telling stories of environmental and internal stress and how to overcome it.
When crosstalk is facilitated between the skin and its microbiome, your skin has the information it needs to reach its fullest potential. In addition to the skin’s intrinsic barrier function, our largest organ is capable of much more than we take it for. In fact, the two major layers of our skin, the epidermis and dermis, both harbor a bilateral connection with the rest of the body. For instance, Mitsuhiro Denda from Shiseido Research Center suggested that our skin acts as a “third brain” and that our epidermal or outermost skin cells, keratinocytes, actually contain “multiple environmental sensors and a sensory information-processing system (that) generates a variety of hormones and neurotransmitters with the potential to influence whole-body states and emotions.” Our dermal layer then houses fibroblasts and mast cells that act as “a central player of the skin stress responses,” according to research published by scientists Ying Chen and John Lynga. These cells “are activated by stress, and in turn they also produce stress hormones…This could lead to a vicious cycle of stress-induced…events.”
In other words, your skin is acting as not only a physical barrier but a sensory network that is capable of speaking with the entirety of your body’s systems, including your brain and digestive system, also known as the “second brain”. This ability “plays a significant role in adapting whole-body physiology, and also emotional response, to changing environments.”
This astounding research suggests that the importance of our skin goes way beyond aesthetics or barrier function—that we may need to start thinking of skin as a sentient organ that plays a key role in the function of surrounding organs and even mood. The weight this carries for skincare, body-care, and even mental wellbeing is immense, as Chen and Lynga’s 2014 research states, “as of today there is no proven medical treatment that can either prevent or treat stress-induced or exacerbated skin conditions or aging.”
If the skin-brain connection so heavily rests on moderating internal and external stress, the application of clinically studied, soothing topicals to aid in these areas could be a critical addition to a holistic regimen.
So what if we were to treat the skin, its microbiome, and the rest of the body as the interdependent network that it is? How would that affect what products we apply topically? What products we ingest?
As a formulator for almost 40 years, I feel a responsibility to this revelation—a responsibility to acknowledge the interdependent and ancient relationship of not only the skin and its microbiome, but the body and its microbiome. I seek ingredients that uplift this crucial relationship and embrace the interdependence and shared majesty of The 5 Kingdoms* (microbial, fungal, animal, botanical, and algae). The deeper we look, the more we realize we are not one bigger or better than the other, instead we are all a part of each other and ultimately, evolving together.
By Paul Schulick
 Zilber-Rosenberg, Ilana (2008). "Role of microorganisms in the evolution of animals and plants: the hologenome theory of evolution". FEMS Microbiology Reviews. 32 (5): 723–35.
 Margulis, Lynn; Fester, René (1991-01-01). Symbiosis as a Source of Evolutionary Innovation: Speciation and Morphogenesis. MIT Press.