A study has found that about one in 10 people may have traces of class A drugs on their fingerprints despite not taking them, but it’s possible to differentiate them from those that have.

The study from the University of Surrey, published in Clinical Chemistry, tested the fingerprints of 50 volunteers who said they had not used drugs and about 25 who had taken cocaine or heroin in the past 24 hours.

Of those who were drug-free, about 13 percent had traces of cocaine on their fingerprints and 1 percent had a trace of heroin, even after washing their hands. But by setting a cut-off level, the researchers could tell who had simply been exposed to the drugs in the environment and those who were active users.

"Believe it or not, cocaine is a very common environmental contaminant – it is well known that it is present on many bank notes,” Dr Melanie Bailey, from the University of Surrey, said in a statement. “Even so, we were surprised that it was detected in so many of our fingerprint samples.”

The test was done by putting their fingerprints on chromatography paper and then extracting substances from them with solvents, which were then analyzed. Traces of the class A drugs were found on the aforementioned 13 percent of non-drug users.

The researchers also tested the possibility that drugs could be transferred via a handshake, with the drug-free volunteers asked to shake the hands of the drug users. Fingerprints taken after did show traces of the drugs, suggesting they can be transferred, but it was still possible to tell the difference between the two groups.

There were a couple of limitations with the study, notably that the sample size was somewhat small and that all the volunteers came from the same locale of Surrey in the UK.

But Dr Bailey told IFLScience that it still proved their concept. And this same team has previously shown that researchers can use fingerprints to tell within seconds whether a person has used cocaine. The test is especially alluring because it is non-invasive, hygienic, and can't be duped. Fingerprints can also quickly be attributed to an individual.

"Fingerprints provide a really convenient way of screening for drug use," Dr Bailey told IFLScience. "We anticipate the test will be used in workplace testing or for the rehabilitation of drug users."

In England and Wales, it's estimated that about 2.7 million people aged 16 to 59 took illicit drugs in 2015 and 2016, with more than 8,500 taken to hospital with drug-related mental health disorders and 2,500 deaths from drug misuse.