Skin microbiome is a community of microbes that live on the surface of human skin or inside its associated structures such as skin pores (hair follicles), sebaceous 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. For example, bacteria such as Propionibacterium acnes is attracted to more oily areas on the skin, Corynebacterium predominates in moist sites, whereas beta-Proteobacteria and Flavobacteriales are more prevalent in dry skin areas. 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 individual differences and the activity of other microbes that colonize the same site. For this reason, the skin of each of us carries unique microbial communities shaped by many factors including our genetics, nutrition, life style and the activity of our hormones and immune system.
Skin is the largest organ in our body that provides protection and controls our body 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” (SIS). Skin immunity is achieved through interaction between the 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. The age, sex, ethnicity, endocrine system, neurological system and genetics influence both our skin microbial communities and skin immune defense. The immune regulation of the skin in health and in disease is currently the subject of intense 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 skin barrier breach that occurs because of skin injury or surgical interventions. Bacteria such Staphylococcus aureus, Propionibacterium acnes and Staphylococcus epidermidis are especially common pathogens in implant-associated infections (IAI).