Pores for thought: how sweat reveals our every secret, from what we’ve eaten to whether we’re on drugs
When I deposited my index fingerprint on a laboratory slide so that Simona Francese could analyse it, I felt as if I was giving her the password to my body’s secrets. Most forensic scientists examine a fingerprint’s pattern but Francese, a forensic scientist from Sheffield Hallam University, analyses the chemicals left behind in those whirls and swirls. Her aim is to develop techniques that will allow her to extract identifying information about people at a crime scene from the sweaty residues they leave behind.
Fingerprints are inked with sweat, a body fluid that holds revealing information about our health and our vices.
Our sweat glands source perspiration from the watery parts of blood, and any chemicals flowing around your circulatory system can, in principle, leak out of your sweat pores.
When she examined my fingerprint’s chemistry using a technique called mass spectrometry, Francese easily found evidence of my morning coffee, thanks to the caffeine circulating in my blood. Had I spiked my latte with a shot of whisky or snorted a line of cocaine as a breakfast chaser, Francese could have detected that, too. In fact, in collaboration with law enforcement, she has previously tested her technique on a stalker’s fingermark left behind on a window sill, and found chemical evidence that he had been indulging in alcohol and cocaine – something he had also admitted to law enforcement.
It’s not just mind-altering substances that emerge in our sweat. One nurse in South Africa turned her sweat red thanks to an intense predilection for spicy tomato corn chips. Scientists matched the red pigment in her sweat to the chip’s flavouring, immortalising her fondness for Nik Naks in medical literature.
Researchers are also working on ways to distinguish vegans from meat eaters, based on chemicals left behind in sweaty fingerprints, as well as biological sex and age. “To people trained in chemistry, it’s obvious that fingerprints aren’t just inanimate objects,” Francese says. “There is organic and inorganic matter there to be discovered.”
Sweat also holds markers of disease – certain cancers, for example – as well as a potpourri of other chemicals that hint at our more private selves, such as stress hormones.
But it’s not just forensic scientists who are curious about the sweat we leave behind throughout the day. Although fingerprints are the most minuscule of sweaty marks, many of us leave oodles of perspiration behind on spin bikes, yoga mats, T-shirts, bike