Before biting into an apple or giving your child a plum for a snack, you probably give the fruit a rise under the tap – a ritual so ingrained, it’s become second nature. Likewise, when preparing a meal, you rinse tomatoes, eggplants, cucumbers, or any other vegetables in the flow of a tap before cutting them up.

But what if washing alone isn’t enough? Perhaps it’s time to start peeling them, too.

That’s what scientists report in the American Chemical Society’s Nano Letters journal, based on research using new high-tech imaging analysis. This enables the detection of very small quantities of chemical compounds, such as pesticide or herbicide residues.

The scientists’ research may surprise those who feel reassured by rinsing an apple before taking a bite: they suggest that a trickle of clear water won’t be enough to rid the fruit of chemical residues, quite simply because pesticide compounds are able to travel and penetrate the pulp.

“Notably, the distribution of pesticides in the apple peel and pulp layers is visualised through Raman imaging, confirming that the pesticides penetrate the peel layer into the pulp layer (∼30 μm depth). Thus, the risk of pesticide ingestion from fruits cannot be avoided by simple washing other than peeling,” the abstract of the study highlights.

As a result, it’s better to peel a pear or Golden Delicious before eating it, if you don’t want to ingest (too many) pesticide residues. Note that pesticides don’t penetrate the fruit all the way to the core, which might be a small consolation.

Earlier this year, a study by Générations Futures revealed that 73.1% of non-organic fruit contained at least one pesticide residue, as did 45.8% of non-organic vegetables. The analysis was carried out between 2017 and 2021 on 21 fruits and 31 vegetables.

The most contaminated foods were grapefruit, nectarines, peaches, celeriac, and lettuce.