The bacteria and chemicals found on human skin have been sampled and mapped across the human body. The result is a series of 3-D images revealing the thousands of microbes and molecules people carry with them -- or on them -- each day.
The maps show the unique composition of skin -- the body's largest organ -- on the bodies of two test subjects, and can reveal the food they eat, medicine they consume and body products they use.
This interplay between the microbes found on skin with the surrounding environment can provide insight into someone's food and drug use, personal hygiene, and beauty practices.
"We wanted to understand the driving factors for microbial communities on skin," says Pieter Dorrestein, professor of pharmacology at the University of California, San Diego, who led the study. This is the first time the molecules and bacteria found on the surface of human skin have been mapped in such detail across the body and may one day further unveil the skin's role in health and disease.
"It's well known that these microbial communities have an impact on health and disease ... we have an opportunity to think about precision medicine," he said.
The chemical signature found on the skin is thought to be unique to an individual. It harbors specific combinations of bacteria -- 850 were seen in this study alone -- and a distinct mix of molecules from foods eaten, such as citrus, and even medicines taken. "If we extended this to other people we'd see [drugs such as] antidepressants and antifungals," says Dorrestein.
The team took swabs from 400 regions of the skin across one side of the human body in two volunteers who hadn't washed, shampooed or moisturized for three days. "We wanted to increase the number of microbes and decrease the beauty products," says Dorrestein.
Human skin has a surface area of up to 2 square meters and is the body's main interface with the environment. "It's your first exposure to a lot of different chemistry and microbes," says Dorrestein.
But despite the lack of washing among the volunteers, 14% of the molecules identified -- of the 20,000 chemicals and bacteria searched for by the team -- were from cosmetic and beauty products, such as shampoos and deodorants. "Personal care products we use every day really stay on the skin ... for moisturizer this would be advantageous," says Dorrestein. This persistence was found despite human skin shedding millions of skin cells each day.
"A lot can be known in terms of an individual and their lifestyle," he adds.
Location, location, location
Different types of bacteria are known to predominate certain parts of the body, due to factors such as moisture, which can aid their growth and development. For this reason, when mapped, the feet were the largest home for bacteria such as staphylococcus, whereas bacteria associated with conditions such as acne were predictably found in higher numbers on the face and upper back.
"But we don't know what they're doing there," says Dorrestein for whom this study is just a snapshot. The aggregation of chemicals in certain places around the body -- such as sunscreen around the neck -- need further research to be understood. "At this point it's a mystery," he adds.
Until now, little has been understood about the make-up and locations of the skin's microbial ecosystem. "[This mapping] adds a new dimension to the study of the complex community of microorganisms that live on normal human skin ... which provides interesting new information," says Thomas Kupper, head of dermatology at Brigham and Women's Hospital in Boston, United States. "[But] The full potential of this approach is as yet unrealized ... we need to consider these complex and uncharacterized interactions between the cells of our skin, the multitude of microbes that inhabit the skin, and how chemicals applied to our skin interact with both."
The findings are based on insight from only two volunteers and provide purely a first glimpse into this burgeoning new field of research -- providing a baseline to further investigate the workings of human skin. The team hope human skin composition could be one day be monitored or altered to improve, or prevent, diseases including skin allergies such as psoriasis and dermatitis.
"We want to know what's a healthy microbial community," says Dorrestein about the mapping technology and hopes it could be used to find indicators of what might be going wrong in an individual. "We can then improve health."