There is a greater diversity of bacteria living on the human forearm than on any other part of the body, according to a new study.

On average, 44 different types of bacteria reside on the forearm, compared with 19 species living behind the ear, says the study by the National Human Genome Research Institute in the US.

Reporting the results of the study, ScienceNow says: "Microbes that live in and on our bodies outnumber our own cells ten to one." Intriguingly, these microscopic passengers were found to be evenly distributed around the body.


The team took skin samples from 20 sites on the bodies of 10 healthy volunteers who had been asked to wash with a mild soap for one week and come to the lab after not washing for 24 hours.

The skin sites were picked to represent three microenvironments: oily, moist and dry. Oily sites included between the eyebrows, beside the nose, inside the ear, back of the scalp, and upper chest and back. Moist areas were inside the nose, armpit, inner elbow, webbed area between the middle and ring fingers, side of the groin, top fold of the buttocks, behind the knee, the bottom of the foot and the navel. Dry areas included the inside surface of the mid-forearm, the palm of the hand and the buttock.

Samples were analysed using gene-sequencing technology to identify the microbial RNA (Ribonucleic acid), which could then allow them to identify the bacteria on the skin. They found more than 112,000 bacterial gene sequences, which they classified into more than 1,000 species.


In broad terms, the research revealed that a far wider variety of bacteria live on our skin than was previously believed. It also showed that dry and moist skin had a broader variety of microbes than oily skin. "Our results underscore that skin is home to vibrant communities of microbial life, which may significantly influence our health," said the study's primary author, Elizabeth Grice.

The team also sampled some of the volunteers twice, with visits four to six months apart, to see if the "skin microbiome" changed over time. The team found that the stability of certain microbial communities was dependent on where they were on the body. The greatest stability was found in samples from inside the ear and nose, and the least stability was found in samples from behind the knee.

The research is hoped could be used in efforts to combat the growing problem of methicillin-resistant Staphylococcus aureus (MRSA), a bacterium that can cause life-threatening infections. The team found that a significant proportion of people have colonies of S. aureus inside their noses, and that these colonies also exist in the crease of skin outside the nose. "Not only does our work shed new light on understanding an important aspect of skin biology, it provides yet another example of how genomic approaches can be applied to study important problems in biomedical research," said Eric D. Green, co-author of the study.