Human skin is home to far more bacteria than previously thought

A recent study of bacterial communities on the skin will aid the understanding of certain skin conditions and speed efforts to understand the complex genetic and environmental factors involved in diseases such as eczema, psoriasis, and acne.

The US National Human Genome Research Institute in Bethesda, Maryland, has just published a study in the journal Science. According to their research, there are 100 times more bacterial species living on our skin than previously thought. These findings emerged because of a new method employed in studying the bacterial communities living on us. This method used a genetic analysis of the DNA found on the skin rather than taking skin swabs and then trying to grow the microbes in the laboratory. Using this new method, the researchers took samples from 20 areas on the bodies of 10 healthy people and ran them through a DNA screening process. This revealed bacteria belonging to 19 different phyla. Most of these skin bacteria do us no harm and keep the skin healthy by preventing infections from more harmful microbes. The same regions of skin on different people tended to house similar communities of bacteria. This may explain why some skin complaints only tend to affect certain areas of the body and will help answer questions such as why psoriasis normally affects the outer elbow yet eczema often affects the inner area of the elbow. The greatest numbers of bacteria were often found in the moist, hairy parts of the body like the armpits. However, the greatest diversity of microbes were found on the forearm, where on average 44 species of bacteria were found. The least diverse habitat was behind the ear. Researchers found that the skin can be divided into three broad ecological habitats – oily, moist, and dry. The oily sites contained the most uniform mix of microbes and included the eyebrows and sides of the nose. The moist areas included the inside of the nose and the webbed areas between the fingers. The dry areas included the palm of the hand and the buttocks. Bacterial cells are roughly a thousand times smaller than human cells but are far more numerous – indeed there are about 10 times as many bacterial cells living on the skin as there are human cells in the body.