Editors' ChoiceDERMATOLOGY

Beauty is only skin deep

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Science Translational Medicine  08 Apr 2015:
Vol. 7, Issue 282, pp. 282ec60
DOI: 10.1126/scitranslmed.aab0846

The largest of our organ systems, skin is the interface between us and the world. Though we may think of skin as inherently part of oneself, it is actually a highly complex balance between self, microbe, and environment. Bouslimani et al. used detailed molecular and spatial characterizations to describe the interplay between our skin, its microbiome, and the chemicals in our environment.

Approximately 400 sites on each of two volunteers (one male and one female) were swabbed twice. One swab was used to define the microbiome with 16S ribosomal RNA amplicon analysis. The other swab was used to define the site’s metabolite, lipid, and protein composition using mass spectrometry (MS). This study, the most comprehensive in the field, is notable for several reasons. MS analysis is a technically well-defined task. However, making sense of the vast data generated posed a major challenge. The authors combined multiple reference libraries so that MS spectra could be accurately annotated; correlated redundant results into molecular families; discriminated between skin, microbial, or environmental origins; correlated molecular and bacterial diversity; and created three-dimensional (3D) spatial maps of these molecular and bacterial populations on the human skin. Among the key findings was that different body regions revealed distinct populations of microbes and chemicals. Moreover, only 41% of MS spectra matched between the two volunteers, suggesting a high degree of interindividual variability. The single largest category of detected and annotated chemicals (8% of the total) derived from beauty products or cosmetic ingredients. This was true even though volunteers had not showered or applied hygiene products for 3 days prior to sampling.

Despite this comprehensive approach to skin analysis, there are still notable limitations, driven primarily by an incomplete spectral library annotation (<3% of the total MS spectra could be annotated). The distribution of sources for compounds found on the skin will change as the annotation of detected molecules improves. However, studies such as this serve as the groundwork upon which to build a more comprehensive understanding of how we interface with the world around us.

A. Bouslimani et al., Molecular cartography of the human skin surface in 3D. Proc. Natl. Acad. Sci. U.S.A. 10.1073/pnas.1424409112 (2015). [Full Text]

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