One of the largest human-associated microbial habitats 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.
13 Total bacterial counts on the hands of HCWs have been reported to range from 3.9 x 104 to 4.6 x 106 colony-forming units per cubic centimeter.
14-16 A recent study concluded that a typical hand surface harbors >150 unique species-level bacterial phylotypes and a total of 4,742 unique phylotypes have been identified across all hands examined.
17 The most abundant genera (
Propionibacterium, Streptococcus, Staphylococcus, Corynebacterium, and
Lactobacillus) were found on nearly all palm surfaces. Although there appears to be a core set of bacterial taxa commonly found on palm surfaces, pronounced interpersonal variation in bacterial community composition was noted: women appear to have significantly higher diversity than men, and community composition is further affected by handedness and time since the last hand washing.
17