ABSTRACT: Skin sampling has been conducted as described in the [Molecular cartography of the human skin surface in 3D Amina Bouslimani, Carla Porto, Christopher M. Rath, Mingxun Wang, Yurong Guo, Antonio Gonzalez, Donna Berg-Lyon, Gail Ackermann, Gitte Julie Moeller Christensen, Teruaki Nakatsuji, Lingjuan Zhang, Andrew W. Borkowski, Michael J. Meehan, Kathleen Dorrestein, Richard L. Gallo, Nuno Bandeira, Rob Knight, Theodore Alexandrov, and Pieter C. Dorrestein PNAS April 28, 2015 112 (17) E2120-E2129] by swabbing areas of skin with a cotton swab and extracting the swabs using ethanol. The samples were stored in -80 C freezer until analysis. The GC-MS analysis was carried out on a Thermo Scientific TRACE 1310 GC-MS [TG-5ms 5; length, 30 m; ID (inner diameter), 0.25 mm; film thickness column, 0.25 um] and a TSQ 8000 EVO mass spectrometer (Thermo Fisher Scientific), equipped with electron ionization (EI) source, equipped with robotic sampler system. 1uL aliquot of sample was injected into the GC inlet maintained at 250C. The GC protocol was as follows: starting temperature 40 C (hold of 0.1 min), 15 C/min oven ramp to 280 C (hold of 0.1 min), and a 3 min hold period to purge the column. The helium carrier gas was set to constant 2 mL/min flow, splitless injection mode was used throughout. The scanned m/z range in a single quadrupole was 35-350 Th with solvent delay of 4 minutes.