The Washington PostDemocracy Dies in Darkness

Crud on your cellphone screen reveals more about your life than you might think

A woman uses a smartphone in Los Angeles. (Frederic J. Brown/AFP/Getty Images)
Placeholder while article actions load

Are you a coffee drinker? Do you slather on sunscreen? How about mosquito repellent? You don’t have to tell a team of University of California at San Diego biochemists — they just need to borrow your phone. To them, the answer to such questions lies within a thin layer of grime on your cellphone’s screen and case.

In a proof-of-principle study, published Monday in the Proceedings of the National Academy of Sciences, the scientists investigated 39 people’s phones for what they called “molecular lifestyle signatures.” These chemical traces of our day-to-day activities and external environments accumulate as tiny bits of crud and detritus on our phones.

Hygiene and beauty products, pesticides, diet and medicines can leave signatures. “All of these chemical traces on our bodies can transfer to objects,” UC San Diego biochemist and study author Pieter Dorrestein said in a statement. “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.”

The scientists took hundreds of samples swabbed from volunteers’ phones and right hands. Thanks to a technique called mass spectrometry, which sorts molecules on the basis of their mass and electrical charge, the researchers could compare the signatures on a phone to a chemical database. Swabs from the back of the phone could reveal what was left behind by hands, and chemicals detected on the front of phone, the scientists wrote, could shed light on a person’s face.

They could tell if someone used an antifungal medication, skin inflammation or hair loss treatments, antidepressants and eye drops. Trace amounts of caffeine indicated a tea or coffee drinker. The scientists found a molecule associated with citrus fruits on the hand and phone of one subject. That person, naturally enough, was a “large consumer of oranges and uses a lot of citrus-based cleaning products,” the biochemists wrote in the paper.

Plant sugar and sunscreen indicated a person spent time outside. Capsaicin, the active ingredient in chili peppers, revealed a spicy food fan. Some signatures, like the anti-mosquito pesticide DEET, remained detectable for up to five months after application.

“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,” study author Amina Bouslimani, a postdoctoral researcher at UC San Diego’s Skaggs School of Pharmacy, said in the statement.

This was not the first research into the dirt that gloms onto our cellphones. One 2011 study estimated that, in 1 in 6 devices swabbed, fecal bacteria called a phone home. (Although, to put that finding in context by way of mangling Sting: We are spirits in the bacterial world. Germs cover almost everything, and the ones that dwell happily in your lower gut are no exception.)

The goal of this recent research was not to create a way to identify a particular person by phone. The signatures were not so specific that they could replace a fingerprint. Rather, the scientists envisioned that the technique could be used to gather details about someone’s routine — a boon, the authors said, for fighting crime. (And to the National Institute of Justice, which funded the study.)

“The molecular analysis would help a criminal investigator in narrowing down the owners of the object (e.g., a suspect of a crime scene or understanding the habits of a terrorist),” they wrote in the paper, “by identifying specific lifestyle characteristics from objects they touch.”

More from Morning Mix

An Ohio lawyer hypnotized six female clients and then molested them. Now he’s going to prison.

U-Va. students, faculty ‘deeply offended’ by university president quoting Thomas Jefferson, the school’s founder

Restaurant denies free Veterans Day meal to black veteran after man in Trump shirt accuses him of lying