Normal Microbial Flora of the Skin

One of the largest human-associated microbial ecosystems is the skin. To understand the objectives of different approaches to hand hygiene and associated adverse effects, knowledge of the normal bacterial flora of the skin is essential. Different areas of normal human skin are colonized variably primarily by aerobic bacteria and bacterial density may be as high as 107 cells per square centimeter.11 Total bacterial counts on the hands of HCP have been reported to range from 3.9 x 104 to 4.6 x 106 colony-forming units per cubic centimeter.12-14

Hand surfaces harbor >150 unique bacterial phylotypes and a total of 4,742 phylotypes have been identified across all hands examined.15 The most abundant genera (Propionibacterium, Streptococcus, Staphylococcus, Corynebacterium, and Lactobacillus) are found on nearly all palm surfaces. Although there appears to be a core set of bacteria commonly found on palm surfaces, women appear to have significantly higher diversity than men; and microbial community composition is further affected by handedness and time since last washing hands.15