In Love? True Togetherness Means Sharing the Same Microbes

Love is the spice of life — it is also the microbes that couples share through sickness and in health, through the bathroom and in a hallway.

The skin is our largest body organ. Your skin is the most significant protective barrier between squishy, vulnerable innards and a pathogen-filled world. Complex and layered, the skin plays hosts to a multitude of organisms that call us home. We all have microbes covering our bodies — most of them are harmless, and some even help crowd out bad bugs.

Despite our personal feelings about our skin and the skin of our lovers, it is a pretty harsh region for microbes. Continually shedding, relatively dry, and subject to antibiotic soaps or disinfectants, our skin is often not a happy place for the communities of organisms that live there. But still — researchers say between one million and one billion microbes are having a party in each square centimeter of your skin all the time.

Research published in the journal mSystems took a look at how much of these microbes we truly share with our significant others.

Microbial ecologists at the University of Waterloo in Canada collected swabs from 10 sets of sexually active couples who were living together. They swabbed microbes from 17 different areas of the body, for a total of 330 samples.

The study turned up some interesting news, not the least of which is, yes, the microbial resemblance on the skin of couples is so high, that an algorithm could identify who was sleeping with who, with an accuracy rate of about 86%.

There are four bacterial types typically found on the skin — Actinobacteria, Proteobacteria, Bacteroidetes, and Firmicutes. Different types of bacteria live in different areas of the body. Some species prefer wetter areas, while others live where it is drier. There is less bacterial diversity in the skin's sebaceous glands (where acne gets started).

While your hygiene practices influence the bacteria on your skin, your age, health, gender, ethnicity, and geographic location play a big role too. Using gene profiling and statistical analysis, the authors found these results:

Cohabitating couples can be identified by the signature of their skin bacteria 86% of the time. The most similar communities of microbes on partners are on the feet, eyelids, and back.
Sequencing showed Staphylococcus epidermidis was the most common bacteria found on the skin. Usually harmless, S. epidermidis is a common inhabitant of the skin microbiome. In recent years, S. epidermidis has gained a title as an opportunistic pathogen in healthcare settings, much like its more deadly relative, Staphylococcus aureus.
The left and right side of individual bodies scored similarly in microbiota; the highest matches were on the inner thighs and eyelids. Where is the weakest correlation? For individuals, it is the outer nose and the outer thighs.
Skin samples from females were much more diverse than males. Because of the similarities between female skin microbe communities, gender could be determined by algorithm about 80% of the time. Gender could be accurately determined 100% of the time using just microbes from the inner thigh.
Regarding cosmetics and lotions, the research associates the use of a "large number" of skin products with higher microbial diversity. The authors note an earlier study found "skin composition was influenced by hygiene product application," and this study endorsed that finding.

In Love? True Togetherness Means Sharing the Same Microbes — *Image by W.carter/Wikimedia*

Environmentally, couples who consumed several servings of alcohol each day had substantially less microbial diversity, than those who had one serving a month. Apparently, a bacteria called Brevibacterium is present more often on the skin of drinkers, possibly because ethanol is secreted through sweat glands and the bacterium possesses an enzyme that can make use of it.

Not surprisingly, having a canine friend and spending time outdoors translates to higher microbial diversity than those without dogs. An earlier study showed that the skin microbiome of people with dogs was more similar to other dog-owners than to those who did not have dogs.

Researchers believe couples share microbes through a shared environment and direct contact. Noting that humans shed more than one million biological particles per hour, we drench the things we touch and the places we live with our microbial residue. Bacterial forensics can match fabrics, keyboards, and cell phones to their owner — or other users — through the microbe prints left behind.

Sharing microbes is part of the package of being in love. When couples break up — who gets the microbes? That one's easy, you walk out the door with whatever is yours.