The use of drugs is now so widespread that 13% of those who do not take anyway have traces of cocaine on their fingertips (and 1% of heroin). Researchers at the University of Surrey (UK) found this out while they were finalizing a test to detect substance users through a quick fingerprint analysis.

Cocaine and brain: at the origin of the risk of relapse

Touched, or sweaty? The team was looking for a definitive way to distinguish between those who come into contact with cocaine and heroin through environmental contamination and those who are normal users of these substances: they succeeded in establishing a "limit threshold" that reveals genuine consumption, and distinguishing between the superficial traces present on the skin and those secreted through sweat when the drugs are "disposed of" by the body. But it was the figure on the amount of substances dispersed in the environment that left people dumbfounded.

The researchers took fingerprint swabs from the unwashed hands of 50 non-drug users and 15 people who had taken them in the previous 24 hours. However, 13% of non-users showed cocaine traces of the metabolites on their hands (ie produced through metabolism): contamination probably occurs through banknotes, but also due to contact with tables and other "dirty" objects.

Where is he from? According to a 2011 study, 11% of British banknotes come into contact with cocaine or other drugs; more recent research has found traces of drugs on 8 American banknotes out of 10 (but the contamination could concern all the places of wide exchange and contact, not least the happy hour counters, the surfaces of the subways …).

Sponge shot. When the volunteers washed their hands thoroughly, the test correctly identified 87.5% of cocaine users and 100% of heroin users. Tests like these could be used in forensics or to bring about illegal behavior, such as drug use in the workplace, in prisons or in other public contexts.