On your skin - a continuing story

Gee, they are still working out what sorts of things are living on our skin.   Not just bacteria, but archaea:

The researchers conducted both genetic and chemical analyses of samples collected from human volunteers ranging in age from 1 to 75. They found that archaea (pronounced ar-KEY-uh) were most abundant in subjects younger than 12 and older than 60. Their study has been published in Scientific Reports (a Nature journal) in an article titled, "Human age and skin physiology shape diversity and abundance of Archaea on skin."

"The skin microbiome is usually dominated by bacteria," said Hoi-Ying Holman, director of the Berkeley Synchrotron Infrared Structural Biology (BSISB) Program and a senior author on the paper. "Most of the scientific attention has been on bacteria, because it's easier to detect. Based on the literature, six years ago we didn't even know that archaea existed on human skin. Now we've found they're part of the core microbiome and are an important player on human skin."

These are usually tough bugs:

It was not until the 1970s that scientists realized how different archaea were from bacteria, and they became a separate branch on the tree of life -- the three branches being Bacteria, Archaea, and Eukarya (which includes all plants and animals). Archaea are commonly found in extreme environments, such as hot springs and Antarctic ice. Nowadays it is known that archaea exist in sediments and in Earth's subsurface as well, but they have only recently been found in the human gut and linked with the human microbiome....

This study stemmed from a planetary protection project for NASA and the European Space Agency. "We were checking spacecraft and their clean rooms for the presence of archaea, as they are suspected to be possible critical contaminants during space exploration -- certain methane-producing archaea, the so-called methanogens, could possibly survive on Mars," Moissl-Eichinger said. "We did not find many signatures from methanogens, but we found loads of Thaumarchaeota, a very different type of archaea that survives with oxygen."

At first it was thought the Thaumarchaeota were from the outside, but after finding them in hospitals and other clean rooms, the researchers suspected they were from human skin. So they conducted a pilot study of 13 volunteers and found they all had these archaea on their skin.

As a follow-up, which is the current study, they tested 51 volunteers and decided to get a large range in ages to test the age-dependency of the archaeal signatures. Samples were taken from the chest area. The variations in archaeal abundance among the age groups were statistically significant and unexpected. "It was surprising," Holman said. "There's a five- to eightfold difference between middle-aged people and the elderly -- that's a lot."