What Cell Phone Grime Reveals About Lifestyle

Chemical traces left on cell phones show what people eat, what drugs they take and even what cosmetics they use

Dirty Phone
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Sure, a Hello Kitty phone case says a bit about its owner. The phone's apps, texts and photos can also reveal a lot. But it turns out that a huge amount of personal information can be gleaned from the molecules on the case itself. Researchers at the University of California, San Diego, recently detected the “molecular lifestyle signatures” of 39 people by analyzing the traces of daily life in the grit and grime on the screens and cases of their cell phones, reports Ben Guarino at The Washington Post.

The study, published in the Proceedings of the National Academy of Sciences, is a proof of concept determining whether tiny traces of food, medication, skincare products and other chemicals can be used to connect objects to individuals, according to a press release. “You can imagine a scenario where a crime scene investigator comes across a personal object—like a phone, pen or key—without fingerprints or DNA, or with prints or DNA not found in the database. They would have nothing to go on to determine who that belongs to,” senior author Pieter Dorrestein says in the release. “So we thought—what if we take advantage of left-behind skin chemistry to tell us what kind of lifestyle this person has?”

The researchers took swabs from the volunteers’ phones and right hands, Guarino reports. Then using a method called mass spectrometry, which helps researchers identify compounds based on their mass, Dorrestein and his team were able to identify the chemical signatures of the products found on the phones and volunteers. They could discern whether a phone's owner was a coffee or tea drinker by traces of caffeine. They could tell the medications they used—anti-depressants, anti-fungal cream, eye drops, hair-loss treatments. There were also traces of citrus, sunscreen, insect spray and capsaicin from spicy peppers.   

With all of these traces, researchers could assemble a fairly detailed profile of the phone’s owner. Using these profiles, Dorrestein tells Nicola Davis at The Guardian, that the team was able to match the chemical signature of the phone to its owner in 69 percent of the samples. In two cases they were not able to make the match, but in one of those instances the volunteers lived together.

“By analyzing the molecules they’ve left behind on their phones, we could tell if a person is likely female, uses high-end cosmetics, dyes her hair, drinks coffee, prefers beer over wine, likes spicy food, is being treated for depression, wears sunscreen and bug spray—and therefore likely spends a lot of time outdoors—all kinds of things,” says the study’s lead author Amina Bouslimani in the press release. “This is the kind of information that could help an investigator narrow down the search for an object’s owner.”

John Bond, an associate professor in criminology at the University of Leicester tells Davis that he questions the usefulness of the technique when it comes to police work. “The problem is they are not very discriminating things,” he says. “If you were to find a particular brand of cosmetic it is not really going to narrow down for you who you would be looking for.”

In the press release, Dorrestein acknowledges that the trace molecules are not a stand-in for fingerprints, and to make them useful for police would require building a reference database of foods, carpets, paint and other elements people come into contact with on a daily basis.

Beyond forensics, however, he says the chemical signatures have other uses. They could be used by doctors to monitor metabolites on a patient’s skin to determine if they are taking their medication. That same technique could also help researchers understand how different people metabolize drugs or be used to monitor chemicals and pollutant exposure.

The researchers are continuing the study with 80 volunteers, examining the chemical signatures on other personal effects including wallets and keys. In the future, they plan to also investigate the bacteria and microbes on the objects, adding another layer to the chemical signature—a thought that could make you reach for the screen cleaner.

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