The skin microbiome is fairly diverse and key differences exist between different areas of the skin. This section will examine some of the most prominent of these and help provide a good foundation for further discussion.
Since the skin at various sites of the body significantly varies in its microbial communities, one must be very careful when discussing the overall skin microbiome. The skin is home to a number of different ecosystems and environments.
So when discussing the skin microbiome, it is essential to look at each one separately. An easy way to visualize these differences is to simply think of the differences between the locations (palms – dry, armpits – sweaty, face – oily).
Sebaceous areas include places such as side of the nostril, behind the ear, the forehead and the back. These areas have the highest concentration of sebaceous glands, produce significant amounts of oil rich sebum and rely on it for their protection and regulation. The microbial population at these sites is typically the least diverse.
These areas appear to be the most problematic and the majority of pervasive skin conditions affecting the adult population occur here. On normal skin the propionibacterium (actinobacteria) species appears to be the most common and well established .
Moist areas are places like the belly button, armpits, groin, sole of foot, inner elbow, and back of knee. These areas do not produce much of the oil sebum and mostly rely on the production of aqueous sweat for their protection and regulation. The most common bacteria that are active on these skin sites include microbes from the species of staphylococcus (firmicutes) and corynebacterium (actinobacteria) .
Dry areas include the forearm, hand, buttocks, and other areas with little perspiration or lubrication. These areas have been documented to contain the largest diversity of microbes. However, due to the vast variation and the relatively low numbers of each of the microbes in these areas, it is difficult to determine which are actually long-term residents and which are only temporary.
The section examined the general differences of the skin environment and how these effect the unique microbiome composition. Key points include:
- Different areas of the skin have unique properties which effect the relative environment and microbial composition
- Moist areas do not produce sebum, primarily rely on sweat for protection/regulation and are mainly populated by staphylococcus and corynebacterium
- Oily areas of the skin are most abundant in sebaceous glands, rely on sebum for their protection and appear to be the most prone to skin disease
- Dry areas of the skin harbor the largest diversity of microbes, have low microbial density and determining the long-term residents can be difficult