Hold the lime! Could eating citrus zest and peel really be bad for your health?

Do you sprinkle citrus zest on to your cooking or drink hot water with a slice of lemon? According to an Instagram post that went viral last week, you shouldn’t. “Select citrus fruits at Lidl now come with a ‘Peel unfit for consumption’ warning,” posts @wholefoodwarrior. She photographs some of the supermarket’s labels, which list the post-harvest chemicals used to conserve the fruit: azoxystrobin and fludioxonil (limes) and imazalil, 2-phenylphenol, thiabendazole, pyrimethanil and fludioxonil (easy peelers), plus E903 in the peel’s wax coating (both).

The 10,500 comments on the post are largely appalled. So what are these substances? And how worried should consumers be?

Sarah Compson, the head of policy and campaigns at the charity Pesticide Action Network UK (Pan UK), says that many of them are fungicides and known or suspected carcinogens and endocrine disruptors. For example, “Imazalil is a post-harvest fungicide used extensively on citrus fruit during storage and transportation,” she says. “It is a suspected carcinogen and reproductive and developmental toxin. It mostly appears on the skin of citrus fruit, so can be consumed if the zest is used.” Nick Mole, a policy manager at Pan UK, adds that the EU considered a reduction in the maximum residue level for imazalil in 2018, but citrus got a reprieve and changes made in 2019 applied only to bananas, apples and pears.

So while the warning labels may be new, the use of these pesticides certainly isn’t. “Citrus fruit regularly tops our ‘Dirty Dozen’ list of produce found to be high in multiple pesticide residues,” says Compson. “This can include highly hazardous pesticides banned from use in the UK and Europe due to their toxic impact on people and the environment.” This year, grapefruit topped the list, with limes in third place. Over the past five years, soft citrus, oranges and lemons have always featured in the top seven.

Supermarkets are advised, but not legally obliged, to declare the chemicals used in the production and preservation of fruit and vegetables, says Compson. “It’s great to see a supermarket being clear about it. Labelling of the chemicals on citrus at least allows consumers to make more informed choices, but they shouldn’t be exposed to these chemicals in the first place.” Pan UK surveys British supermarkets every two years and ranks them on their efforts to tackle pesticides. In the latest rankings, in 2024, Waitrose and M&S were “leading the way”.

However, when the Guardian contacted Lidl for comment, it emerged that the labels were not a bid for greater transparency, but were apparently added in error. “We can assure our customers that these products have not changed and continue to fully comply with all UK safety standards,” said a spokesperson. “We are working with our supplier to have the packaging label updated to avoid confusion.’”

While all the chemicals (accidentally) listed are classed as safe to use individually at certain levels, it is the “cocktail effect” that most concerns campaigners. “Safety testing isn’t carried out on real-life dietary exposure,” says Compson. As Lidl’s labels revealed, “People are exposed to more than one pesticide at a time. The regulations don’t do enough to protect public health.”

Can’t we just give our oranges and lemons a good scrub when we get them home? “No, sadly not,” says Compson. “The pesticides are present in cells throughout the produce. They are designed to stick to the fruit. It’s not just a case of washing it off.” How about buying unwaxed fruit? “I don’t think it makes enough of a difference,” says Compson.

The only way to cut out these chemicals altogether is to grow your own citrus – easier said than done in the UK – or to buy organic. “We all love a lemon drizzle cake or sticking lime in a gin and tonic,” says Sarah Hathaway, the head of technical at the Soil Assocation. “For people wanting to avoid these chemicals, they are not allowed in organic farming at all, either in production or post-harvest.”

That is likely to mean paying more for your limes. If you would rather take the risk of pesticide exposure – most of us, of course, aren’t eating a huge amount of citrus zest – consider the farmers growing the fruit, who often don’t have the luxury of choice. A report last month found that 46% of farmers worldwide are being poisoned by pesticides every year.