Anyone who’s ever dabbled in drugs and applied for a job has learned to dread the hair test. This test, the more intensely investigative cousin of the urine test, analyzes strand of hair to reveal whether its owner has done drugs in the past three months. Now, forensic scientists have learned how to squeeze even more information out of a strand of hair to reveal more details more personal than they ever thought imaginable.

Introducing their new technique at the 253rd National Meeting and Exposition of the American Chemical Society this week, researchers from West Virginia University report that they can tell a person’s eating habits, body mass index, and even sex from their hair sample.

“We have this chronological record of metabolism and diet in people’s hair,” Glen P. Jackson, professor of forensic science and leader of this project, tells Inverse, noting that this technique could be used to dig up information about a person “that they’re not willing to tell you themselves.”

Details about a person’s eating habits, metabolism, and sex are written in hair at the atomic level, he explains. You just need the right tools to read it. His technique relies, in particular, on examining differences in the ratios of isotopes in the hair; isotopes are atoms of an element, like carbon or nitrogen, that can have varying numbers of neutrons. These atoms link up to form amino acids, which in turn form keratin, the major building blocks of hair. It’s the ratios of different isotopes in the amino acids that ultimately reveal what a person’s been eating, how fast they’ve been burning it off — and, unexpectedly, what their sex is.

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“The amino acid composition of human hair is different depending on male and female — and not just the quantities of the amino acids, but also the isotope ratios of them,” he says.

Jackson envisions his method (involving a rather wordy chemistry technique called “liquid chromatography in conjunction in isotope ratio mass spectrometry”) being used in crime investigations. “There’s a lot that we can learn about, for example, people on parole — whether or not they’re telling the truth — or people being questioned in legal settings. Military applications, tracking people’s history and where they’ve been, what they’ve been eating,” he says. In about ten years, when the cost of his method comes down, he imagines it will be widely used in crime labs for criminal investigations.

In the meantime, the insights it provides us about how the food and drugs we eat are processed inside our bodies are valuable in their own right. He describes how his analysis of one sample from an 11-year-old boy revealed a noticeably higher amount of the amino acid phenylalanine than usual; it turns out that the boy had been taking a drug for autism that contained this amino acid, and Jackson was able to read this in the boy’s hair. It’s likely, he says, that a similar method could be used to detect other compounds — including illegal drugs that evade current strand tests.

Future criminals — and prospective employees — better take note.

Photos via Flickr / Global Voyager