Consider a hairy, moist armpit is a “rainforest” of bacteria, but the forearm is a desert. Scientists surveyed the types of micro-organism living on a healthy human skin and found that it’s much more diverse and crowded than originally thought.
There’s a common notion that all bacteria on the skin are bad, but that’s not exactly true. Some bacteria are beneficial to us, but what they are and where they thrive on the skin has never been studied before. Enter the “Human Microbiome Project” of the NIH, which was created to find out the roles that bacterial communities play on keeping the skin healthy, and which of them cause diseases.
Published on today’s issue of Science, researchers decoded the genes of over 100,000 bacteria from 20 different spots on the skin of 10 individuals. They discovered that the most diverse area of the skin is the forearm, with 44 different species residing on it, and the least diverse is the area behind the ears. When they re-examined the forearm a few months later, the readings changed significantly, obviously since this place is exposed so much to the outside environment. But bacteria on places like the groin and inside the ear didn’t change much.
The NIH researchers also found that certain skin diseases prefer certain sites on the skin. Microbes related to atopic dermatitis prefer behind the knee, which are highly diverse, even and rich places for bacteria to congregate. Psoriasis occurs in the elbows, knees, and creases. Because of increasing public concern about methicillin-resistant S. aureus(MRSA), the bacteria was also surveyed, and found to prefer the moist, soft tissues of the inner nostrils.