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.