In a recent study researchers took swabs of the hands and phones of 39 volunteers. Just by analyzing the samples in a mass spectrometer (a machine that sorts and identifies chemicals) the researchers were able to identify various lifestyle aspects of the volunteers.

For example, they figured out that one participant spends a lot of time outdoors due to the presence of sunscreen components and DEET in their samples. They were also able to positively identify cosmetics like anti-aging creams, prescription treatments like antidepressants and hair regrowth treatments, and even flavor preferences based on trace amounts of spicy compounds or herbs and seasonings.

If it sounds like something straight out of CSI or NCIS there's a reason for that. The study was supported in part by the National Institute of Justice, a branch of the Department of Justice. As the authors write in the paper, criminologists might be interested in using the method to track suspects or tie them to crime scenes, and it may also prove useful for people monitoring terrorist groups. But that isn't the only possible application. These methods could also be used to measure your environmental exposure to pollutants over time or in a particular area.

But there is a catch. In order for the gunk on your phone to be useful in identifying where you've been or what you get up to, there has to be a database in place that can identify all the different signatures left by lotions, foods, and all the other chemicals we come into contact with on a daily basis. As the authors note: “Currently, such a database does not exist and it will take significant community effort akin to the level of fingerprint databases.”