Mandarins – Peel, Wash, Enjoy

Hanna Dias, Kathi Hacker

When eating mandarins, many articles recommend washing your hands or rinsing the fruit after peeling and before eating it. But is that practical in everyday life? And why is this so advisable for these particular fruits? CVUA Stuttgart lays out the facts as to why a trip to the sink before consuming this sweet fruit is worth it for your health. We analyzed 12 mandarins from conventional cultivation for pesticide residues, with and without the peel. The results confirm the many advisors – washing your hands after peeling is definitely worth it!

Mandarin - with and without peel.

Illustration 1: Mandarin – with and without peel

What lands on and in the fruit

Pesticides differ by application and mode of action. So-called systemic substances are absorbed via the roots or leaves of the plant and spread throughout the entire plant and its fruit. These substances enter the plant tissue, so they can't be removed by washing.

Non-systemic pesticides affect the plant surface. These include contact poisons applied to the outside of the plant, most of which remains on the peel.

Mandarins are not only treated with plant protector substances during cultivation, but also often after harvest. This additional application protects the fruit from spoilage during transport and storage. At least some of these non-systemic pesticides and post-harvest substances can be removed by thoroughly washing the fruit with lukewarm water.

A further treatment of citrus fruits includes wax in combination with post-harvest substances, in order to prevent mold and loss of moisture. Typical post-harvest treatment substances include the fungicides imazalil, thiabendazole, orthophenyl phenol and pyrimethanil.

Was there a post-harvest treatment? How will I know?

Packaged mandarins must be labelled with information regarding a possible post-harvest treatment or wax coating, such as "preserved with" or "waxed". For loose mandarins, this information should be found on the crate on the supermarket shelf (e.g. on the cardboard label), as long as the fruit is presented in its original packaging. Labels affixed directly on non-packaged (loose) fruit are only required to indicate whether the substance thiabendazole was used in preserving the fruit and whether it was waxed. Other post-harvest treatment substances, however, fall under different legal requirements and need not be separately indicated on the label.

Info Box

What's the rule for organic?

In organic cultivation neither synthetic pesticides nor post-harvest treatment substances are allowed.

For waxing the citrus fruit, beeswax and carnauba wax are permitted for organic production. The fruit must carry a label indicating that it was waxed.

Analytical Results

In the autumn of 2025 CVUA Stuttgart analyzed 12 samples of conventionally produced mandarins for residues of pesticides and contaminants. The samples were divided and analyzed once in their whole form (peel and flesh) and once in peeled form (flesh only).

Average residue levels of 3.0 mg/kg were detected in the whole fruit, in contrast to 0.31 mg/kg in the flesh alone (both excluding findings for the fungicide phosphonic acid). Thus, around 90 % of the pesticides are found on the peel, whereas only about 10 % are in the fruit flesh. Overall, the average number of different substances found in the fruit flesh (7 substances) was also lower than the number found in the whole fruit (12.5 substances).

Bar chart: Quantities of pesticide residues (sum of all residues excluding phosphonic acid) in the whole fruit and in the fruit flesh.

Illustration 2: Quantities of pesticide residues (sum of all residues excluding phosphonic acid) in the whole fruit and in the fruit flesh. The average pesticide level per sample is strongly influenced by the relatively high levels of phosphonic acid, so the phosphonic acid levels are excluded here. The complete findings are listed in Annex 1, however.

A significant difference between systemic and post-harvest treatment substances was seen in terms of their distribution throughout the fruits, with the systemic-working spirotetramat and post-harvest substance imazalil as examples. Spirotetramat was found in equal amounts in both the whole fruit and the fruit fresh. The post-harvest treatment substance imazalil contained only one-fifth the amount of residue in the fruit flesh compared to that found in the whole fruit.

Bar chart: Systemic substance vs. post-harvest treatment substance.

Illustration 3: Quantities of spirotetramat (systemic substance) and imazalil (post-harvest treatment sub-stance) in the whole fruit and in the fruit flesh.

In addition to the 12 conventional mandarin samples, an organic sample was also analyzed. Neither in the peel nor in the fruit flesh were any determinable residues found.

Conclusion

Mandarins are often treated with post-harvest substances, which end up on the peel. The quantities of pesticide residues found in the whole fruit (peel and flesh) are approximately 10 times higher than those found in the fruit flesh alone. To ensure unadulterated enjoyment of mandarins, CVUA Stuttgart recommends washing your hands after peeling the fruit. This can prevent any pesticide residues adhering to the peel being transferred via your hands onto the fruit flesh and consumed with the fruit. It also makes sense to rinse the whole fruit in warm water before peeling it. In this way, at least part of the residues can be removed before peeling.

Pesticides are not permitted in organic cultivation at any time: not during the growing season and not post-harvest. Those who want to avoid consuming pesticide residues as much as possible should therefore rather purchase organic mandarins.