The lemon eucalyptus, also called Corymbia citriodora or Eucalyptus citriodora, is a large tree that can reach 50 meters in height and is part of the Myrtaceae family. Its leaves give off a strong lemony smell. It is native to Australia and it is one of the favorite meals of koalas who taste its leaves with delight.
Today, it is present around the Mediterranean, in the United States, Mexico, Brazil and Chile. Australian Aborigines used its sap to help heal wounds.
In herbal medicine, leaf essential oil is commonly used for its many beneficial effects on the body, such as its anti-inflammatory, analgesic, antibacterial or insect repellent action. It contains in particular terpene aldehydes such as citronellal, monoterpene alcohols such as isopulegol and citronellol, terpene esters, monoterpenes and sesquiterpenes (LEE & al., 2008 ; SINGH & al., 2012).
These components are found in varying proportions depending on the eucalyptus species. Eucalyptus leaf essential oil can contain more than 70% 1,8-cineole (DHAKAD & al., 2018).
Eucalyptus citriodora essential oil has a high free radical scavenging capacity measured by 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulphonic) acid (ABTS) and peroxyl (MIGUEL & al., 2018).
In another study, it was shown to exhibit moderate to strong antioxidant activity in various antioxidant capacity tests including ferric reducing antioxidant potency assay, ferrous ion chelation, hydrogen peroxide scavenging, scavenging of 2-diphenyl-1-picrylhydrazyl (DPPH) radicals and inhibition of lipid peroxidation (SINGH & al., 2012).
Eucalyptus citriodora essential oil has an anti-inflammatory effect. Indeed, it inhibits the expression of pro-inflammatory mediators such as tumor necrosis factor (TNF)-α, interleukin-6, induced nitric oxide synthase, nitrogen oxide and cycloxygenase-2 in lipopolysaccharide (LPS) stimulated macrophages (HO & al., 2020).
In addition, it exhibits strong anti-inflammatory and analgesic properties in vivo. Indeed, it reduces formalin-induced edema and acetic acid-induced abdominal cramps in rats. These analgesic and antipyretic properties are similar to those of lysine acetylsalicylate (GBENOU & al., 2013). It inhibits carrageenan and dextran-induced rat paw edema, inhibits carrageenan-induced neutrophil migration into the peritoneal cavities, and reduces carrageenan- and histamine-induced vascular permeability in rats (SILVA & al., 2003).
In another study, Eucalyptus citriodora essential oil was shown to induce peripheral and central analgesic effects in models of acetic acid-induced writhing in mice and hot plate thermal stimulation in rats (SILVA & al., 2003).
Eucalyptus citriodora essential oil exhibits antibacterial effects. In particular, it has an inhibitory effect on two antibiotic-resistant strains (Staphylococcus aureus and Pseudomonas aeruginosa), often responsible for nosocomial illnesses (DE BILLERBECK, 2007).
In addition, it exhibits antifungal effect against Pyricularia (Magnaporthe) grisea, Aspergillus spp. and Colletotrichum musae. It inhibits spore production, germination and growth of these three fungal species. The citronellal found in the chemical composition of lemon eucalyptus is partly responsible for this anti-infective effect (AGUIAR & al., 2014).
In addition, the essential oil of Eucalyptus citriodora and citronellal exhibit antihelminthic activity on the gastrointestinal nematodes of sheep. Indeed, they inhibit the motility of Haemonchus contortus 6 hours after exposure, inducing in particular internal ultra-structural modifications in this parasite. In addition, treatment with Eucalyptus citriodora essential oil significantly reduced the amount of eggs excreted in feces by 69.5% (ARAÚJO-FILHO & al., 2019).
Finally, it has a repellent effect against Ixodes ricinus nymphs in vitro. In field trials in tick-infested areas in central Sweden, it demonstrates equivalent first-day action (89%) to blankets treated with 19% diethyl-methyl-benzamide (DEET), a powerful insect repellent (JAENSON & al., 2006).
Food of choice for koalas who love it, you now understand why koalas never have fleas, ticks or gastrointestinal worms.
