Unlike the microbiome of the epidermis, the microbiome of the dermis appears to be consistent across ages and between genders, researchers report in mBio (Feb. 11, 2020; 11(1):e02945-19). In this study, skin samples were taken from the knees and hips of Danish patients scheduled to have knee surgery. Sample donors did not have any skin infections and were otherwise healthy. “We found that the microbiome in epidermis is unique. It is very different depending on age and gender. On the other hand, the microbiome in dermis is the same—regardless of age and gender. This has not been shown before,” said co-author Lene Bay, in a press release. Bay is a postdoctoral researcher at the department of immunology and microbiology at the University of Copenhagen. The authors say the findings will have an impact on the understanding of the skin and its bacteria, and may improve the understanding of why skin disorders occur and how to treat them. “It is important that we drop the assumption that we are all different, and that the microbiome of the skin does not matter very much. We do know that bacteria play a major role in skin disorders. Therefore, we need to understand the bacteria and the skin in its three dimensions,” said co-author Dr. Thomas Bjarnsholt, professor at the department of immunology and microbiology, University of Copenhagen. “Especially in connection with skin disorders, you see that the healthy skin balance disappears and that there is a build-up of some dominant bacterial species. Hopefully, this knowledge will help us to understand for example how eczema occurs and which irregularities are taking place in the skin,” said Dr. Bjarnsholt. Understanding the microbiome of the dermis may also improve understanding how infections occur in acute and surgical wounds. For knee and hip surgery, the risk of surgical wound infections is 1% to 2%, the authors note. “[Infection in knee surgery] is not a huge problem, but there are many knee and hip operations on a yearly basis, and we will see more and more in the future. That is why it will represent a growing problem. We believe that the dermis' microbiome has a bearing on the risk of infection after surgery,” said Bay. “When you cut through the skin during surgery, you may be pushing some of these bacteria even further down. And the underlying bacteria are not cleansed with surgical ethanol like the bacteria on [the] epidermis. What significance that may have and whether it may be the cause of post-surgery infections is one of the things that we need to study more closely,” said Bay. The researchers' next step will be to study other skin areas. Knees and hips are dry skin areas. Therefore, researchers would also like to study oily and moist skin habitat, such as the upper back and the armpit. In the long term, the researchers would also like to study skin samples from diseased patients in order to be able to compare the microbiome in dermis from healthy and diseased persons.