metagenomics of skin microbiome
Sampling was performed by applying pressure to a 2 x 2 cm area of one side of the forehead in a circular motion for 60 seconds with sterile cotton swabs (Fisher #22-029-630) pre-moistened with a swabbing solution (Tris-EDTA (TE) buffer + 0.5% Tween-20 + 1% TritonX-100). Sample locations were noted and swabs were placed in cryotubes with in 700l DNA/RNA Shield Buffer (Zymo Research # R1100-50) at -80 C until sample extraction time. For skincare compound applications, subjects applied a cotton round saturated with either SLES solution (3% in water) or RL solution (3% in water) to the treatment side of their forehead for 30 seconds, twice a day. We processed skin swabs by extracting DNA and RNA using the ZymoBIOMICS DNA/RNA miniprep kit (cat# R2002), and prepared metagenomics library  with the Illumina Nextera XT DNA library preparation kit (Illumina, cat# FC-131-1096).