Thursday, 27 February 2014

Will Eating Oranges Kill Parasites?

Oranges are a popular and relatively
affordable fruit. It would be great if
claims that they kill parasites were
true. Image by Rosino: CC BY-SA 2.0
Have you read that oranges have antiparasitic properties, and that eating them can help keep parasites away? Is there any truth to this claim? It’s certainly true that many substances derived from plants are antiparasitic, so what’s the evidence for oranges?

Antiparasitic Oranges - The Science

A search for papers on the antiparasitic properties of oranges yields very little, but when I looked at orange essential oil and parasites, I found some research. Studies have used orange oil to treat parasites in fish, sheep, gerbils, and in the lab, but none (at least none that I could find) have used human subjects.

A study by Squires and colleagues investigated whether an orange oil emulsion would kill a roundworm parasite in gerbils and sheep. These researchers found that, at a high enough dosage, the treatment killed a significant number of the worms, suggesting that it might be useful in animal parasite control.

In contrast, in a 1990 Japanese study, “many essential oils were found to be nematocidal to the larvae of dog-roundworm, Toxocara canis,” but essential oil of oranges wasn’t one of the star examples. In the lab, only about a third of larvae were killed by orange oil, and only after 24 hours of exposure.

Hirazawa and colleagues studied whether plant essential oils could be used to kill a flatworm that infests puffer fish. They looked at caprylic acid (derived from palm and coconut oil, and human milk), orange oil, peppermint oil, and cinnamon oil, exposing the parasites to the oils in the lab. The researchers found that orange oil is the only one of the four that does not affect this parasite.

Other studies found orange oil to be ineffective at killing honey bee mites, and ineffective at killing kissing bugs, the vector of Chagas' disease. So it looks like orange oil may kill some parasites, under specific conditions, but it’s no panacea. The good news is that it does appear to be useful, if used properly, in the control of subterranean termites.

Oranges vs Orange Essential Oil

Essential oils are derived from plants using a distillation process. They are highly concentrated essences, and orange oil is generally made from the peel of the fruit. Obviously, eating an orange is very different from ingesting orange oil (and I’m not sure that this would be safe). I wonder how many oranges one would have to consume (including the peel) to get any benefit, assuming you had a parasite that they would kill.

I believe it’s safe to say that there is no convincing evidence that orange oil is a good way to keep parasites at bay, and there is no evidence at all for oranges.



Hirazawa, N., T. Ohtaka, and K. Hata. 2000. “Challenge trials on the anthelmintic effect of drugs and natural agents against the monogenean Heterobothrium okamotoi in the tiger puffer Takifugu rigripes.” Aquaculture, 188, 2000

Nakamura N., F. Kiuchi, Y.Tsuda et al. 1990 "Nematocidal and bursting activities of essential oils on the larvae of Toxocara canis." Shoyakugaku Zasshi: 44(3).

Squires J., J. Foster, D. Lindsay et al. 2010. "Efficacy of an orange oil emulsion as an anthelminticagainst Haemonchus contortus in gerbils (Meriones unguiculatus) and in sheep."  Am.Vet Parasitol. Aug 27;172(1-2):95-9. doi: 10.1016/j.vetpar.2010.04.017. 


  1. I just discovered your wonderful website and blog, and soon I will add your Parasites book to the shelf.

    On the topic of oranges and parasites, your writing inspired me to do a little reading and an intellectual wander.

    Limonene is the main ingredient extracted from orange peels into orange oil. Comparing that against the molecule for thymol (which is effective against nematodes), it looks like the thymol's O atoms are one of the differences.

    Peel back the orange and you have inside ascorbic acid, which has alot of O's. What do you get when you mix orange oil (limonene) with ascorbic acid?
    Alas I am not a chemist, but it looks interesting. Is this a binary weapon against certain parasites?
    Are there survival/propagation benefits (for the orange tree) of wrapping the fruit’s ascorbic acid in a limonene cover?

    The next thought that occurred to me was “how do other animals eat oranges?”

    At lunch today I peeled my orange, so maybe I missed out on something. Also I did not swallow the seeds, walk a long distance, and, uh, leave the seeds in a new place, so I probably fouled up the orange’s long-successful evolutionary strategy for propagation. ;-)

    According to Wikipedia, fruit bats crush an orange to get the juice. Would that crushing mix limonene with ascorbic acid?

    Let me take a side-path here.
    Interestingly, the fruit bat is a reservoir for Ebola virus.
    The fruit bat, like primates, does not produce ascorbic acid and so must acquire the form of Vitamin C via food.
    Dogs, however, do produce ascorbic acid, and can catch Ebola, and can be asymptomatic.
    Hmmmmm. Pigs also catch Ebola, they do tend to develop the disease, and they do produce ascorbic acid. I thought it would be good to see what the hog farmers say, so I found NationalHogFarmer’s guidance that healthy pigs do not have a Vitamin C requirement, but supplementing vitamin C seems to help reduce mortality from PCVAD. The article suggests that certain immunological challenges impact the pig’s production of Vit C. Again, hmmmm.

    Time is out on this wander, but lots to wonder about.

    Thanks for writing the article on orange oil.

    Leander, TX
    (just outside of Austin)

    1. I think you've just outlined a whole career's worth of research!

      Two thoughts: I believe thymol was once the drug of choice for treating hookworm infections; however, like many treatments for parasites, it was a matter of giving enough to kill the worms without doing the same to the host! Nasty stuff.

      I can readily believe that limonene and even ascorbic acid are part of the orange tree's defenses against its own parasites. Maybe we should focus on kumquats which, of course, are most delicious eaten whole.

      Thanks for your fascinating thoughts. :-)

    2. Hi Rosemary,

      Your thoughts on kumquats are interesting as well. Thank you.

      Wikipedia says the main ingredient in kumquat’s essential oil (from the peel) is
      so I see why you made the association with kumquats.
      Wikipedia didn’t say anything about the inner fruit of the kumquat. A little extra Bing’ing shows that, like the orange, kumquat contains ascorbic acid. If indeed limonene + ascorbic acid can be a binary weapon against certain parasites, then I presume this applies to the kumquat as well as to the orange.

      There may be more to learn from the kumquat.
      Check out this excerpt from

      The Cantonese often preserve kumquats in salt or sugar.[citation needed] A batch of the fruit is buried in dry salt inside a glass jar. Over time, all the juice from the fruit is diffused into the salt. The fruit in the jar becomes shrunken, wrinkled, and dark brown in color, and the salt combines with the juice to become a dark brown brine. A few salted kumquats with a few teaspoons of the brine/juice may be mixed with hot water to make a remedy for sore throats.[citation needed] A jar of such preserved kumquats can last several years and still keep its flavor.[citation needed]

      In the Philippines and Taiwan, kumquats are a popular addition to green tea and black tea, either hot or iced.

      [end of excerpt]

      Looking at the minor ingredients listed for the essential oil, I saw something that intrigues me. With respect to alpha-pinene, look at the “Reactivity” section of
      They show how certain molecules that include chlorine, i.e. HCl and NOCl, combine with alpha-pinene. It would be interesting to look at what happens over time when you combine NaCl and alpha-pinene (a la what the Cantonese do). I’m sure the salt acts as a preservative for the kumquats, but there may be other chemical/medicinal molecular insights to be gained. I wish I had access to a building full of chemists--I would ask one of them to do an analysis on the brine.

      Moving on, the excerpt mentions kumquats in tea.
      According to
      4-Hydroxybenzoic acid ... is one of the main catechins metabolites found in humans after consumption of green tea infusions.

      On a hunch I Bing’d for
      +"4-hba" +nematodes
      and found
      4-HBA extends lifespan of wild-type C. elegans under normal and stress conditions.

      I sifted through a lot more than I presented here, and there are enough clues to make me wonder if a long time ago someone in Asia noticed that adding kumquats to tea gives an anti-parasitic health benefit, and if the chemistry can be elucidated with modern analysis capabilities.

      Alas, I am out of time, but saying that, I want to address your comment about thymol. Thymol is present in culinary thyme, and in thyme tea, so it is still widely used at low concentrations. Personally I hate the stuff, but I can see the logic of why it became a common ingredient in cooking.
      I’ve always thought it would be fun to write a cookbook that discusses the relationship between regionally-used spices/ingredients and the parasites indigenous to those same regions. A sure eyebrow-raiser in the kitchen, but probably a very select audience. ;-)

    3. I hit "publish" too soon. I mean to make more clear that if the tea's 4-HBA can benefit nematodes as well as the human host, then the addition of the kumquat and therefore limonene + ascorbic acid might harm the nematodes and prevent them from reaping the benefits of 4-HBA.


      John Beach
      Leander, TX
      (just outside of Austin).

  2. Hours after my previous post, it dawned on me to Bing for
    +monoterpene +porcine
    and what do you know?
    I found an existing food additive for piglets that contains thymol, vanillin, citric and sorbic acids.
    I wonder if this stuff would prevent a pig from becoming an Ebola reservoir?

    Just so no one wonders, I have no affiliation with, nor do I have a stake in the success of the additive.


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