It seems we learn more and more about the microbiome every day. And these days, it's about way more than just the gut microbiome—it's about the skin, mouth, and even the lung microbiomes, too. In their new book, The Whole-Body Microbiome, Jessica Finlay, Ph.D., and Brett Finlay, Ph.D. share the latest science on the bacteria that inhabit all areas of our body—and what that means for our health. Here's some of what they had to say about the skin microbiome and how it influences the health of our skin, especially as we age.
We are completely coated in microbes. There are approximately one million bacteria composed of hundreds of species on every square centimeter of our bodies. Skin contains the body's fourth-largest collection of microbes after the gut, oral, and vaginal areas. Have a look at your hand—there are over 150 species on one palm alone. Although we tend to think of our skin as homogeneous, from a microbial point of view it comprises immensely different environments: Both the moist, warm areas—the "tropics" of your groin, armpits, navel, and between the toes—and drier surfaces, the "deserts" of your forearm, buttocks, and hands. Although we don't know why, the dry areas of the skin have the most diverse composition of microbes but lower microbial numbers. (Just like plants, microbes need moisture to grow.) There are even microbial differences between the sides of our bodies. One study found that we share 68 percent of microbes between the left and right forearms, but only 17 percent between the left and right hands. While alarming at first, this difference actually makes perfect sense: In the last five minutes, which hand did you use to pick up a pen, scratch your head, or tap out a message on your phone? The things our two hands touch vary wildly, whereas our forearms are used in a much more even capacity.
What do these teeming colonies of surface microbes do to us? In addition to out-competing harmful microbes, they also produce molecules that counter specific pathogens. For the most part, they go about this business silently, breaking down fats and other molecules produced by our skin for food so that they can be our strongest first line of defense. To do this well, they also interact with the immune system, reporting on the state of our skin surface, so the immune system can better respond to and defend against foreign invaders.
One microbe that illustrates these concepts is Cutibacterium acnes (C. acnes, previously known as Propionibacterium acnes), so named for its involvement in acne. This microbe breaks down the triglycerides (fats) in sebum, an oily secretion that is produced by our skin glands. Breaking down these molecules produces fatty acids, which in turn acidify the skin. This acidity is necessary to block pathogens such as Staphylococcus aureus (S. aureus) from causing infections on the skin, as the bacterium prefers a more neutral pH. In fact, people with atopic dermatitis (an inflamed skin disease) have lower levels of beneficial microbes and higher levels of pathogenic S. aureus.
Another common skin inhabitant, Staphylococcus epidermidis (S. epidermidis), works for our benefit by secreting molecules that kill pathogens like S. aureus and Group A Streptococcus—pathogenic bacteria that can cause a variety of illnesses, ranging from minor skin infections and medical conditions such as pimples, cellulitis, atopic dermatitis, abscesses, and strep throat to life-threatening diseases such as pneumonia, endocarditis, and sepsis. A recent study showed that certain normal skin microbes, including S. epidermidis, secrete these antimicrobial peptides in order to kill off the competition vying to live on the skin. The researchers found that when these beneficial microbes were added to the skin of patients for 24 hours, the number of S. aureus (the pathogen) decreased. The take-away from all this seems to be that we can actually benefit from this ongoing microbial warfare on our skin. But if we lose the beneficial microbes, we also lose their protection.
While you wouldn't want to go around guessing people's ages by their faces, from a microbial perspective it's completely possible to do so. Because microbes are our essential companions as we age, and respond to our ever-changing internal and external environments, we can tell someone's age within a decade just from analyzing a microbial swab of the forehead. Remarkably, people over the age of 50 have distinctly different microbial signatures than younger adults.
Scientists are just beginning to uncover exactly how and why the skin's microbiome shifts and loses diversity as we age. No matter the reason, this phenomenon speaks to the critical need to enhance and maintain your skin microbiota as a robust ecosystem throughout life. Cosmetic companies have picked up on this fact: You can now find commercial skin care products that incorporate emerging microbial scientific discoveries into topical applications. At the time of writing, L'Oréal, for example, patented several bacterial treatments for dry and sensitive skin; Estée Lauder patented a skin application with Lactobacillus plantarum; and Clinique sells a foundation with Lactobacillus ferment. Products such as La Roche Lipikar Baume AP, used to treat eczema and other dry skin issues, likewise include bacterial additives to help restore a healthy skin microbiome and to stop itching. Keep an eye out for these and more emerging microbial skin care lines.
Despite this progress, Dr. Greg Hillebrand, a senior skin scientist at Amway, a major health and beauty corporation, believes there is still a serious need for new methods and treatments for aging skin. "The pace of innovation in the anti-aging category is slowing. Conventional topical products like moisturizers, serums, and essences contain active ingredients aimed at preventing or reversing the signs of aging. Retinoids [a class of active ingredients] remain the gold standard, yet they have been around since the 1980s. The skin microbiota represents an exciting new focus area for us, and it's the next best opportunity to solve many of the challenges associated with aging skin." Dr. Hillebrand's enthusiasm for the use of microbes goes back to 1995. He was sent to Japan by his former employer, Procter & Gamble, to figure out exactly how it worked by studying a prestige skin care line that consisted of a concentrated fungi ferment cultivated, processed, and filtered down into an essence product. "Many of my colleagues at the time did not actually believe it did anything; they all thought it was 'foo-foo dust.' I was only there for a few months when my director from the U.S. came over to see how I was doing. I was excited to share my progress and ideas and met with him and my VP. I told them that I thought it might be possible that the fermented filtrate worked in part by favorably modulating the bacteria on the face in a way that we didn't yet understand. Basically, I was proposing that the use of the product might shift the bacterial composition, perhaps maintaining the good ones and not the bad ones on the face." In 1995, we didn't yet appreciate the concept of "good" and "bad" bacteria on the skin—it simply wasn't conceivable that the skin microflora were important; we certainly didn't culture bacteria specifically to benefit the skin—so it was not surprising that the reaction of Dr. Hillebrand's director to this novel idea was less than enthusiastic.
Thankfully, Dr. Hillebrand followed his hunch. Flash-forward to present day, when he is critically involved in clinical studies and product testing for Amway explicitly focused on the microbes. Much of his team's effort involves data gathering to better understand this emerging area. Amway set up a clinical test site, for example, during a major art event in Grand Rapids, Michigan, where they figured there would be a large variety of patrons of all ages in attendance. The Amway team measured the skin microbiome of hundreds of festival-goers via swabs of their scalps, foreheads, forearms, and nasal/oral areas. The samples showed fascinating differences in microbial communities, especially associated with people's ages. Describing this particular sampling, Dr. Hillebrand grew animated at the prospects of how we can use these microbial differences to enhance appearance and health of aging skin.
While it's gaining traction, he admits that the concept of embracing, rather than eradicating, bacteria on skin remains as foreign today as the discovery of groundbreaking topical products was 30 years ago. But he remains optimistic: "With the microbiome, we can actually do something. The challenge now is to figure out exactly how to leverage science into more effective skin products for real innovation."
Excerpted from The Whole-Body Microbiome: How to Harness Microbes—Inside and Out—for Lifelong Health © B. Brett Finlay, Ph.D., and Jessica M. Finlay, Ph.D., 2019. Reprinted by permission of the publisher, The Experiment. Available wherever books are sold. theexperimentpublishing.com.
Father-daughter team Jessica Finlay, PhD, and B. Brett Finlay, PhD, are the authors of The Whole-Body Microbiome. Jessica is a University of Michigan postdoctoral research fellow who specializes in environmental gerontology and health geography. With degrees from Queen's University and the University of Minnesota, she has won awards for her work and authored publications in leading health, geography, and gerontology journals.