The human body is host to an active ecosystem. We each have microbes such as
bacteria, viruses, fungi and protozoa in our mouth, eyes, ears, nose,
intestines and skin. Although it is popular to believe microbes are dirty,
disease-causing creatures, this is a highly biased and narrow view of microbial
life. Microbes perform many important functions for us, producing vitamins,
helping digest our food, and working as an essential part of our immune system.
Our skin is a rich source of microbes. Adults have between 11,000 (forearm)
and 1.5 million (scalp) bacteria per square centimeter of skin. Babies are
born microbe-free, but rapidly pick up their own set of microbial friends and
reach an adult level of bacterial inhabitants within nine days.
This bacterial colonization is essential for immunity as these resident
microbes defend their territory against disease-causing microbes. In one
experiment, the typhoid bacteria, Salmonella typhi, was smeared on human
skin and, within twenty minutes, was completely destroyed by resident bacteria.
The same Salmonella tyhpi smeared on a glass slide, after twenty
minutes, had remained and reproduced. Constant battle and territorial defense
occurs on our skin. We owe much of our general good health to the results of
these bacterial wars.
There are two main types of microbes on our skin: permanent residents and
transients. Many people believe washing will remove these "bugs and germs."
In fact, studies show even the most vigorous washing does not remove all our
Permanent microbial species live on the surface of the skin and also in deeper
layers. Washing off the surface populations simply encourages microbes in the
lower layers to come and set up camp. However, transient populations, which
are picked up from other people or animals, are generally removed by washing.
So what happens to all those microbes when we shed our skin cells? Unlike our
beautiful reptiles here at Explorit, we humans are messy shedders. We
constantly shed skin cells everywhere. Every day, we produce 10 billion skin
flakes, called squames. In a year, these dead, discarded skin flakes weigh in
at over two kilograms.
Where do all these squames go? Dust. Dust is 90% skin flakes, which are the
favorite food of the peaceful dust mite. They have evolved with humans to live
in protected areas our beds and carpets. The average double bed has 2 million
dust mites. And yes, your bed has them. Numerous epidemiological studies have
found that 100% of homes have dust mites. These peaceful squames-munchers are
the final link in the skin's ecosystem.
Fortunately for our mental health, we humans don't see very well. We can't
visibly detect the millions of 0.4 millimeter dust mites cleaning up our mess
of squames. We don't see or feel our tiny (0.1-0.4 mm) resident skin microbes,
wriggling around, defending their territory against other microbes.
But maybe if we did see and understand them, we would accept and appreciate
their essential contribution to the only real home we have, our body.
Andrews, Michael. 1976. The Life that Lives on Man. New York:
Bodanis, David. 1986. The Secret House: 24 hours in the strange and
unexpected world in which we spend our nights and days. New York: Simon
Lewis, Rick. 1992. The Bugs Within Us. FDA Consumer, v. 26(7):
Sagan, Dorion. 1988. Garden of Microbial Delights: A Practical guide to
the Subvisible World. Boston: Harcourt, Bruce and Javonovich.