Your smartphone is filled with apps, emails and photos all collecting and storing information about who you are and what your lifestyle is like.
Now, new research published in the Proceedings of the National Academy of Sciences shows that our phones carry information about us from sources that have nothing to do with our digital footprint.
By swabbing the surface of a mobile phone and the hand of its owner, researchers were able to chemically match the phone to its user and construct lifestyle sketches for each person just by analysing the dirt.
Although the test wasn't able to biologically identify individuals as well as a DNA test could, the residue left on the phones still contained enough trace chemicals from the body to give a picture of its owner's day-to-day life when analysed using liquid chromatography time-of-flight mass spectrometry.
This highly sensitive technique first separates the chemicals found in the swabbed sample, breaking it down into its individual parts then accelerates those particles through a tube to measure the mass of the emitted ions.
From the study, they found that each person had a very distinct set of chemicals on their hand, almost like a chemical fingerprint which was also found on their phone.
This enabled the researchers to chemically match the phones to their owners.
The swabs determined information about the phones owner including their gender, diet, preferred beauty products, medications taken, health status and lifestyle.
The research found that more molecules transfer from the hand to the back of the phone than to the front and that not all chemicals transfer.
Piperine from black pepper and capsaicin from chilli peppers were found on the hands of some individuals but not on their phones.
The goal of this research was to see if the personal lifestyle of an individual could be learned based on skin-associated chemistries detected on their personal objects.
A follow-up study is now in place analysing other personal items including keys and wallets.
In this phone study, 39 individuals and their phones were swabbed and the method was able to pick up details such as which individuals used high end cosmetics, who used hair regrowth treatment, which person had inflamed skin through their skin inflammation medication and who used eye drops.
The food and beverage choices of an individual were also detectable with high levels of sinensetin-type molecules from citrus fruits detected for one individual who ate a lot of oranges and caffeine traces from coffee and tea drinkers.
In addition to soap and shampoo detection, other products applied to the skin such as sunscreen ingredients and mosquito repellents were also found on the phones indicating the predominantly outdoor or indoor lifestyle choices of an individual.
Interestingly, the mosquito repellent was detected again in a follow up study four months after the individual had applied it showing that some chemicals stick around for a long time after they have been used.
The testing and its chemical database are still in their infancy, but the method has the potential to help support forensic evidence through chemical interpretation of objects found on a crime scene if the DNA or fingerprint information isn't conclusive.
The technique could also be used to give skin molecule read-outs which could provide information about a person's exposure to environmental pollutants and chemical hazards, especially for workers in high-risk chemical workplaces or communities living near potential pollution sources.
Some compulsive smartphone users have described their phones feeling like a part of their body - this new research shows there might be more truth to that than they realised.