Credit Kiichiro Sato/Associated Press
Your phone is pretty much a high-tech bucket of germs. Thousands of microscopic bugs crawl around on its surface. Remnants of dirty, old skin cells smudge its cover. Tiny hairs stick inside its buttons. And your hands have smeared hundreds of chemicals across its surface. The foundation on your face, the antidepressants you take, the shampoo in your shower and even the hard-core mosquito repellent you applied down in Panama four months ago: All of these things leave traces on your hands and phone. That’s why scientists say they can use your phone to learn a lot about your lifestyle.
In a study published in Proceedings of the National Academy of Sciences last week, Pieter Dorrestein, a biochemist at the University of California, San Diego, and his colleagues asked: Can scientists — or maybe one day police investigators — profile a person chemically, based on the objects he or she possesses? They started with your phone, which you touch on average, about 2,617 times a day.
In the study, they swabbed the hands of 39 people, along with their phones, producing hundreds of chemical samples. Then they used techniques from biochemistry to break down, analyze and identify some of the chemicals, matching them with entries in a database of crowdsourced chemical structures. Based on the compounds common to both hands and phones, they made inferences about each person’s lifestyle, like whether they drank tea or coffee, liked citrus fruits or spent time in the sun.
“Not every molecule is a clue,” said Dr. Dorrestein, but those that are “enable you to build a lifestyle sketch of the particular owner or user of that object.”
The study, which was funded by the National Institute of Justice, a research agency of the United States Department of Justice, calls these high-tech deductions “molecular lifestyle signatures,” which could be used in criminal investigations to narrow down a subject pool when DNA or fingerprint evidence doesn’t yield a match. Some legal experts said the technique could improve upon the subjective impressions of investigators.
“This is not different in kind from what happens all the time in criminal investigation, except that it purports to do it more systematically, more scientifically, and potentially more reliably,” Frederick Schauer, a law professor at the University of Virginia who has written about profiling and stereotyping and was not involved in the study, wrote in an email.
The suggestion is worrisome to some forensic scientists. It’s easy to imagine the scenario playing out in a courtroom drama: no match from the DNA in the phone? Pull out the test tubes. Turn on the mass spectrometer. Cue the montage music.
“If you watch a lot of TV and films, you can think this is what’s coming next,” said Brent Turvey, a forensic scientist and criminal profiler.
But Dr. Turvey says that exaggerating the technique’s potential could take the actual science too far too soon, as it has with gunshot residue analysis. As gunshot residue became a greater part of investigations, forensic scientists determined that it can turn up in places other than the hands of a person who fired a gun, potentially creating false positives.
While chemical profiling could one day find its way to a crime lab for use in limited circumstances, Dr. Schauer said there was a fat chance it would ever make it into the courtroom. Expert evidence has to reach an extremely high standard for admission at trials, which the technique may not be able to meet.
Jonathan Koehler, a behavioral scientist at the Northwestern University Pritzker School of Law, worries that if this technique were to take off, investigators might ignore or undervalue other leads and push courts to prematurely admit evidence based on potentially inaccurate inferences.
“I don’t smoke and am rarely around cigarette smoke, but I just happened to be around someone yesterday who was smoking up a storm,” he said. “So what would detection of nicotine on my iPhone really say about my lifestyle, other than something really misleading?”
Dr. Dorrestein, the study’s lead author, acknowledged that even if a chemical profile could narrow down a pool of suspects, later proving someone’s identity, and perhaps their guilt beyond a reasonable doubt, ultimately comes down to a full investigation.
That means your filthy phone is more likely to reveal that you remembered your meds or sunscreen than it is to nail you in court.