Scientists build smartphone user profiles by studying their dirty screens

Molecular traces left on cell phones can be used to reveal the owner's lifestyle(Credit: Amina Bouslimani and Neha Garg)

Smartphones really are filthy things. Their screens are so good at gathering up microbes that they actually carry around 10 times the bacteria of most toilet seats. This is bad news if licking your smartphone screen is a favorite past time, but good news if you're in the forensic science game looking for new ways to gather evidence. By analyzing these and the other molecules left behind on these displays, scientists have worked out a way to paint pictures of user lifestyles that include details like diet and whether they've used sunscreen – information that may one day help crime scene investigators close in on a suspect.

The inspiration for the work came from earlier research carried out at the University of California, San Diego. A team lead by Pieter Dorrestein, professor at the university's School of Medicine, built 3D models mapping the locations of hundreds of molecules and microbes on two adult human bodies. The team was surprised to find that even though the participants agreed not to use personal hygiene and beauty products for three days leading up to the study, it was exactly these types of molecules that showed up in the greatest numbers.

"All of these chemical traces on our bodies can transfer to objects," says Dorrestein. "So we realized we could probably come up with a profile of a person's lifestyle based on chemistries we can detect on objects they frequently use."

So Dorrestein set out to explore this possibility. Thirty-nine participants took part in his latest study, which saw him and his team swab almost 500 samples from their phones and hands. Using mass spectrometry and a crowdsourced database, the team identified enough molecules within the samples to produce a lifestyle profile of each participant.

The molecular traces include medications such as anti-inflammatories, anti-fungal skin creams, antidepressants, hair-loss treatments and eye drops. Food molecules were also found, such as citrus molecules, caffeine, herbs and spices, while sunscreen ingredients and DEET mosquito repellant showed up even months after they had last been used.

The researchers point out that in its current form, the approach has its limitations. While it can offer a general outline of a person's lifestyle, it isn't intended to provide a one-to-one match like a fingerprint might. But by adding more and more molecules to the reference database, bit by bit they can make the method more precise. To this end, the team has already moved onto a larger study involving 80 participants and including other personal, frequently handled items like keys and wallets.

"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 first author Amina Bouslimani, an assistant project scientist in Dorrestein's lab. "This is the kind of information that could help an investigator narrow down the search for an object's owner."

The research was published in the journal Proceedings of the National Academy of Sciences.

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