The skin microbiome is a community of microbes that live on the surface of human skin, or inside its associated structures such as pores (hair follicles), sebaceous glands and sweat glands.
Skin microbes include many different species of bacteria, fungi and viruses, which colonize different areas based on their affinity for the specific skin environment found in that particular area. For example, bacteria such as Propionibacterium acnes is attracted to more oily areas on the skin, Corynebacterium is predominantly found in moist sites, whereas beta-Proteobacteria and Flavobacteriales are more prevalent in areas of dry skin. In addition to these general environmental preferences, the degree to which each species colonizes a specific site is also heavily influenced by the human host’s individual biological and immune differences, as well as the activity of other microbes that colonize the same site. For this reason, each individual’s skin carries unique microbial communities that are shaped by many factors including our genetics, nutrition, lifestyle and the activity of our hormones and immune system.
The skin is the largest organ in our body, providing protection and helping to control our body’s homeostasis. Our skin is not a passive protective barrier, but a network of effector cells and molecular mediators that constitute a highly sophisticated network known as the “skin immune system”. Skin immunity is achieved through the interaction between external and internal skin layers and compartments, which operate in balance with the skin colonizing microbes. Skin disease ensues when this fine balance is disturbed. Genetics, hormones, the neurological system and the external environment can all influence the growth and activity of our skin’s microbial communities and alter or reduce the efficacy of the skin’s immune defence. The immune regulation of the skin, in both healthy and diseased states, is currently the subject of intense scientific research.
Skin colonizing microbes are not only associated with various skin diseases, but, under certain circumstances, they can also induce severe internal infections. Most common are infections caused by a breach in the skin barrier, due to skin injury or surgical interventions. Bacteria such as Staphylococcus aureus, Propionibacterium acnes and Staphylococcus epidermidis are especially common pathogens in implant-associated infections (IAI).