Recent advances have increased our understanding of the human microbiome, including the skin microbiome. Despite the importance of the hands as a vector for infection transmission, there have been no comprehensive reviews of recent advances in hand microbiome research or overviews of the factors that influence the composition of the hand microbiome. A comprehensive and systematic database search was conducted for skin microbiome-related articles published from January 1, 2008 to April 1, 2015. Only primary research articles that used culture-independent, whole community analysis methods to study the healthy hand skin microbiome were included. Eighteen articles were identified containing hand microbiome data. Most focused on bacteria, with relatively little reported on fungi, viruses, and protozoa. Bacteria from four phyla were found across all studies of the hand microbiome (most to least relative abundance): Firmicutes, Actinobacteria, Proteobacteria, Bacteroidetes. Key factors that impacted the hand microbiome composition included temporal and biogeographical dynamics, as well as intrinsic (age, gender) and extrinsic (product use, cohabitants, pet-ownership) variables. There was more temporal variability in the composition of the hand microbiome than in other body sites, making identification of the "normal" microbiome of the hands challenging. The microbiome of the hands is in constant flux as the hands are a critical vector for transmitting microorganisms between people, pets, inanimate objects and our environments. Future studies need to resolve methodological influences on results, and further investigate factors which alter the hand microbiome including the impact of products applied to hands. Increased understanding of the hand microbiome and the skin microbiome in general, will open the door to product development for disease prevention and treatment, and may lead to other applications, including novel diagnostic and forensic approaches.

Hands play a critical role in the transmission of microbiota on one’s own body, between individuals, and on environmental surfaces. Effectively measuring the composition of the hand microbiome is important to hand hygiene science, which has implications for human health. Hand hygiene products are evaluated using standard culture-based methods, but standard test methods for culture-independent microbiome characterization are lacking. We sampled the hands of 50 participants using swab-based and glove-based methods prior to and following four hand hygiene treatments (using a nonantimicrobial hand wash, alcohol-based hand sanitizer [ABHS], a 70% ethanol solution, or tap water). We compared results among culture plate counts, 16S rRNA gene sequencing of DNA extracted directly from hands, and sequencing of DNA extracted from culture plates. Glove-based sampling yielded higher numbers of unique operational taxonomic units (OTUs) but had less diversity in bacterial community composition than swab-based sampling. We detected treatment-induced changes in diversity only by using swab-based samples (P < 0.001); we were unable to detect changes with glove-based samples. Bacterial cell counts significantly decreased with use of the ABHS (P < 0.05) and ethanol control (P < 0.05). Skin hydration at baseline correlated with bacterial abundances, bacterial community composition, pH, and redness across subjects. The importance of the method choice was substantial. These findings are important to ensure improvement of hand hygiene industry methods and for future hand microbiome studies. On the basis of our results and previously published studies, we propose recommendations for best practices in hand microbiome research.

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