Our skin is home to huge numbers of bacteria, fungi, and viruses, and each of us has a unique fingerprint of our particular mix of microbial communities that is defined by its genetic makeup or microbiome.
Writing in the journal Cell, researchers from the National Human Genome Research Institute (NHGRI) and the National Cancer Institute (NCI) – both in Bethesda, MD – suggest their findings should help us better understand how skin diseases develop.
While most of the microbes that live on our skin are friendly and cause no harm, some have been linked to skin disorders, such as acne, eczema, and psoriasis.
Studies of the more harmful skin microbes have helped us understand, for example, why eczema tends to affect moist areas such as skin in the bends of the arms and legs, while psoriasis tends to appear on the outside, more exposed parts of elbows and knees.
In previous work, the researchers had already established that microbial communities not only have a strong preference for particular sites, but that each person has a unique genetic fingerprint of the range of microbes on their skin.
Within-person stability greater than between persons
For the new study, the researchers wanted to explore a less well-studied area, and that is how the microbial communities on our skin change over time and whether these fluctuations have a role in health and disease.
They found to their surprise that skin microbial communities remain remarkably stable over time, despite coming into regular and frequent contact with other sources of bacteria, fungi, and viruses, including other people, clothing, surfaces, and bacteria-laden objects.
The researchers analyzed the genetic makeup of microbes in skin samples taken from 12 healthy volunteers at three successive intervals, ranging from 1 month to 2 years apart. The samples came from 17 sites on the body. For the analysis, they used an approach called “metagenomic shotgun sequencing.”
In their paper, senior study authors Dr. Julie Segre, of the NHGRI, and Dr. Heidi Kong, of the NCI, and colleagues note how they found “an individual’s short- and long-term community similarity significantly exceeded similarity between individuals,” and that these findings are similar to “observations in gut and other communities.”
However, they also found that the stability of the microbial communities varied from person to person, and to different extents with different strains.
For example, oily sites – such as on the back and in the tube that runs from the outer ear to the middle ear – showed the least variation over time, as did highly exposed and dry sites, such as the palms.
But on skin areas with a much larger range of different microbes, such as the feet and moist sites, the researchers found the microbial fingerprint was much less stable over time. They suggest this could be because of the influence of personal hygiene or because the sites are exposed to more variable environments.
Because they only studied a small number of healthy adults, the researchers now plan to widen their investigations to include patients with eczema and skin disorders that arise because part of the body’s immune system is missing.
“Future studies can use the knowledge of the relative stability of the skin microbial communities in healthy adults to understand how various exposures or disease state may alter these skin microbes.”
Dr. Julie Segre
For example, researchers could study acne patients to find out if specific strains of skin microbes flourish during flare-ups or change when patients take antibiotics.