Study: 1 in 8 people have cocaine on their hands, even if they’re drug-free

LONDON — Sober? That doesn’t necessarily mean that you’ll pass a drug test, a new study finds. That’s because one in every eight people are walking around with traces of cocaine on their hands — and there’s a good chance they have no idea where it came from.

Researchers at the University of Surrey in the UK recently tested the fingerprints of 65 volunteers, 50 of whom reported not using drugs, to determine whether regular citizens could mistakenly test positive. Perhaps so: 13 percent of participants who self-reported being clean had traces of cocaine on their fingertips, while another one percent had minute levels — about one metabolite — of heroin, the researchers found.

Person holding out their hand
A new study finds one in eight people are walking around with traces of cocaine on their hands — and they likely have no idea where it came from.

A subsequent part of the experiment had the group’s drug-free volunteers shake hands with its drug-using subset, which allowed the researchers to analyze the sober volunteers’ fingerprints afterwards. The fingerprint analysis showed that tests could still reliably differentiate between actual use and secondary contact, findings that law enforcement could use in criminal proceedings.

In case you’re wondering, that magic cut-off point is one metabolite.

“Believe it or not, cocaine is a very common environmental contaminant— it is well known that it is present on many bank notes. Even so, we were surprised that it was detected in so many of our fingerprint samples,” says researcher Dr. Melanie Bailey, a lecturer in forensic analysis, in a university media release. “[However], we can give those tested the piece-of-mind of knowing that whatever the result of the test may be, it was not affected by their everyday activities or shaking hands with someone that had taken drugs.”

The results held true even after participants washed their hands.

Although most drug tests are still done through more traditional means, such as blood or urine, the researchers firmly believe that fingerprint testing is the wave of the future.

“There are many factors that set fingerprint testing apart — it’s non-invasive, easy to collect and you have the ability to identify the donor by using the sample,” explains Mahado Ismail, the study’s lead author. “Our study will help to add another robust layer to fingerprint drug testing.”

Ismail et al. published their findings in the Sept. 2017 edition of the journal Clinical Chemistry.