What is unclear is the extent to which human behaviors influence the composition of skin microbes. Some species are better at defending our skin than others ( Christensen & Brüggemann, 2014), just as some species produce different odors than do others ( Leyden et al., 1981). Since the 1950s it has been clear that the precise composition of the skin biome influences its effectiveness as a defensive layer against pathogens ( Eichenwald et al., 1965), and contributes to bodily odors ( Shelley, Hurley & Nicholas, 1953).
This life includes bacteria, fungi, Archaeans, bacteriophages, and even animals such as nematodes and Demodex mites ( Marples, 1965 Grice & Segre, 2011 Kong & Segre, 2012). Like the gut or the mouth, the human skin is covered with life. Although stopping the use of deodorant and antiperspirant similarly favors presence of Staphylococcaceae over Corynebacterium, their differential modes of action exert strikingly different effects on the richness of other bacteria living in armpit communities. Collectively these results suggest a strong effect of product use on the bacterial composition of armpits. In addition, individuals who used antiperspirants or deodorants long-term, but who stopped using product for two or more days as part of this study, had armpit communities dominated by Staphylococcaceae, whereas those of individuals in our study who habitually used no products were dominated by Corynebacterium. Sequence-based analyses suggested that individuals who habitually use antiperspirant tended to have a greater richness of bacterial OTUs in their armpits than those who use deodorant. These culture-based results are in line with sequence-based comparisons of the effects of long-term product use on bacterial species richness and composition. In addition, when antiperspirants were subsequently applied, bacterial density dramatically declined.
In doing so, we find that when deodorant and antiperspirant use were stopped, culturable bacterial density increased and approached that found on individuals who regularly do not use any product. Here we experimentally manipulate product use to examine the abundance, species richness, and composition of bacterial communities that recolonize the armpits of people with different product use habits. One obvious potential explanation for this variation has to do with the use of personal hygiene products, particularly deodorants and antiperspirants. The human armpit has long been noted to host a high biomass bacterial community, and recent studies have highlighted substantial inter-individual variation in armpit bacteria, even relative to variation among individuals for other body habitats. Understanding the factors that account for this variation, however, has proven challenging, with many studies able to account statistically for just a small proportion of the inter-individual variation in the abundance, species richness or composition of bacteria. Microbiomes vary greatly from individual to individual. An ever expanding body of research investigates the human microbiome in general and the skin microbiome in particular.