Scientific Name(s): Backhousia citriodora F. Muell.
Common Name(s): Lemon myrtle, Sweet verbena myrtle
Medically reviewed by Drugs.com. Last updated on Jan 1, 2023.
The leaves and flowers of lemon myrtle are used in tea blends and beverages, biscuits, breads, confectionery, pasta, syrups, liqueurs, flavored oils, packaged fish (salmon), and dipping and simmer sauces. A topical 10% solution of lemon myrtle essential oil showed a 90% reduction of symptoms in children treated for Molluscum contagiosum. The leaf paste, essential oil, and hydrosols have antibacterial and antifungal activity against Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Candida albicans, methicillin-resistant S. aureus (MRSA), Aspergillus niger, Klebsiella pneumoniae, and Cutibacterium acnes. The Complementary Medicines Evaluation Committee (CMEC) of the Australian Therapeutic Goods Administration (TGA) reported the proposed use as an antiseptic therapy in the treatment of pimples and acne. B. citriodora leaf oil is approximately 98% citral. Clinical trial data are lacking to recommend use for any indication.
Clinical trial data are lacking to provide dosing recommendations.
Contraindications have not been identified.
Information regarding safety and efficacy in pregnancy and lactation is lacking. Caution is warranted with topical B. citriodora oil use during pregnancy.
None well documented.
Information regarding potential adverse reactions is limited.
Lemon myrtle 1% oil has been shown to be low in toxicity and could be safely used in topical antimicrobial products. The majority of research has been conducted on the compound citral as a common ingredient. Citral and citral oil are considered safe at a 1% dilution and have US Food and Drug Administration (FDA) generally recognized as safe (GRAS) status.
B. citriodora is a small genus, with 6 species located in tropical regions of eastern Queensland and northeastern New South Wales, Australia.
Backhousia is a tree that grows up to 20 m, but in cultivation rarely exceeds 5 m. Leaves are opposite, glabrous, lanceolate, and dark green, and measure 100 mm. The fruit is a dry indehiscent that splits into 2 chambers.(Hegarty 2001, Konczak 2010, Pengelly 1991) Lemon myrtle can be cultivated successfully in cooler areas when young plants are protected from frost.(Ryder 2005) It is a hardy plant that tolerates all soils, except those that do not drain well, and though slow-growing, it responds well to slow-release fertilizers. Lemon myrtle has also been successfully cultivated indoors. B. citriodora is best propagated from cuttings, because the seeds are difficult to germinate. When cultivated, moist, rich soils are preferred.(Hess-Buschmann 2004)
B. citriodora is grown for the strong lemon fragrance of the foliage. The prolific apical clusters of white 4-petaled flowers are attractive on branches in the summer and autumn.(Hayes 2003, Konczak 2010) The species is known to have at least 2 chemical variants; chemovars and their respective aromatic essential oils in the leaves are rich in citral or its close chemical relative citronellal.(Hegarty 2001) Citral is more commonly used for its sweet, fresh, lemon-type perfume and flavor.
B. citriodora was previously incorrectly known in forestry literature as "lemon ironwood," but in modern use in foods or drinks, it is called lemon myrtle. Lemon ironbark (Eucalyptus staigeriana) also contains citral, but in lower concentrations.(ANPSA 2022)
The genus is named after the British botanist James Backhouse (1794 to 1869), and the specific epithet, citriodora, comes from the richly scented lemon leaves. Traditional use is not well documented due to limited density, but it is likely that Australian Aboriginal people used the leaves, which are prominent in bushfoods, as a seasoning.(Hess-Buschmann 2004) The flowers and fruits are used as flavorings, antiseptics, and surface disinfectants, and in foods as a natural antimicrobial agent.(Hegarty 2001, Hess-Buschmann 2004) The leaves and flowers are used in tea blends and beverages, dairy biscuits, breads, confectionery, pasta, syrups, liqueurs, flavored oils, packaged fish (salmon), and dipping and simmer sauces.(Konczak 2010)
The plant was named by the German-Australian botanist Baron Ferdinand von Müller in 1853, but its use was not expanded until the 1990s when it was evaluated as a crop plant and cultivated.(Hess-Buschmann 2004)
In 1889, botanist Joseph H. Maiden, working for the innovative flavor and fragrance German company Schimmel & Co, reported on the potential use of lemon myrtle for commercial production. He was supposedly the first to identify the ingredient citral, which accounts for 90% of the essential oil found in B. citriodora. Other lemon-flavored oils contain less citral (eg, citrus [3% to 10%], lemongrass [75%], tropical verbena [74%]) but are more common due to their lower cost. With the addition of many acres of trees and more research, there is the potential for greater commercial opportunity regarding B. citriodora.(Hegarty 2001)
B. citriodora citral levels can be higher than 80% in the essential oil from the leaves. The approximate essential oil components are 40% neral (alpha citral) and 50% geranial (beta citral). Identification of the essential oils was authenticated by enantioselective capillary gas chromatographic and isotope-ratio mass spectrometry coupled online with capillary gas chromatography.(Nhu-Trang 2006) The Australian TGA and the CMEC indicate that B. citriodora leaf oil is approximately 98% citral.(CMEC 2000)
The other main chemovar, citronellal, can contribute up to 80%, which makes the leaves unsuitable for commercial use. The oil provides most of the aroma and flavor.(Hegarty 2001, Hess-Buschmann 2004)
The leaves of B. citriodora contain 0.33% to 0.86% essential oil. Antioxidant properties were found in Backhousia by testing crude extracts with the Trolox-equivalent antioxidant capacity assay and Australian Quarantine and Exports Advisory Council (now known as the Biosecurity Advisory Council) methods. Total phenolics were 88.1%, radical scavenging was 56.6%, and antioxidant activity was 46.7%.(Hegarty 2001) Antioxidants were found at 102, 60, and 31 mg gallic acid equivalents per gram of dry weight, respectively.(Konczak 2010)
Uses and Pharmacology
Citral has sedative, antiviral, and antifungal properties. Although not clinically proven, citral is also considered to have antitumor properties.(Pengelly 1991)
In vitro data
The leaf paste, essential oil, and hydrosols have demonstrated antibacterial and antifungal activity against S. aureus, E. coli, P. aeruginosa, C. albicans, MRSA, A. niger, K. pneumoniae, and Propionibacterium acnes.(Wilkinson 2003, Zuas 2007) Water, alcohol, and hexane extracts of leaves were tested against food-borne bacteria (Enterococcus faecalis, E. coli, Listeria monocytogenes, P. aeruginosa, Salmonella enteritidis, Salmonella typhimurium, and S. aureus).(Burke 2004, Dupont 2006, Hayes 2002, Hayes 2003) Gram-positive and gram-negative bacteria were treated with 0.125% and 0.5% concentrations of B. citriodora essential oil. The bacteria were inhibited at 0.0625% v/v.(Zuas 2007) One gram of Backhousia leaves was extracted in 50 mL of methanol, and the 15.7 mg/mL extract was found to be effective against 2 gram-positive bacteria (Bacillus cereus, Bacillus subtilis) and 2 gram-negative bacteria (Aeromonas hydrophilia, Pseudomonas) in a disk diffusion method.(Cock 2007)
Potential antiviral activity of citral extracted from lemon myrtle has been demonstrated in silico against a key enzyme responsible for replication of SARS-CoV-2.(Ullah 2022)
Thirty-one children were treated with a 10% solution of B. citriodora for the viral infection M. contagiosum. Of the treated group, 81% demonstrated a 90% reduction of lesions in 30 days compared with the vehicle, olive oil.(Burke 2004, van der Wouden 2009)
In vitro data
Anti-inflammatory activity of lemon myrtle (B. citriodora) ethanolic extract has been demonstrated in vitro in a dose-dependent manner, with significant reductions in interleukin 6 (IL-6) and tumor necrosis factor alpha observed. The strongest effect was proportional to the phenolic compound content.(Kang 2020, Shim 2020)
In vitro data
Antioxidant activity of B. citriodora ethanolic extract has been demonstrated in vitro in a dose-dependent manner, with the strongest effects correlated to phenolic compound content.(Kang 2020, Shim 2020)
Animal and in vitro data
The aqueous extract of B. citriodora leaves promoted proliferation of skeletal muscle satellite cells, with casuarinin determined to be one of the active compounds involved in the effects. Myoblasts were unaffected. Both the extract and casuarinin upregulated IL-6 expression in the satellite cells, which is essential for their activation, proliferation, and subsequent muscle hypertrophy. These results were further supported by oral administration of the extract and casuarinin in rats.(Yamamoto 2022)
Essential oil extracted from the leaves of B. citriodora demonstrated potent and long-term (3-hour) repellent activity against Rhipicephalus sanguineus, a tick species believed to be a vector of a number of human pathogens, including Rickettsia species, which causes spotted fever. Repellent activity at 1 hour after application was significant (P=0.005).(Lunguinho 2021)
Clinical trial data are lacking to provide dosing recommendations.
Pregnancy / Lactation
Information regarding safety and efficacy in pregnancy and lactation is lacking. Caution is warranted with topical B. citriodora oil use during pregnancy.(TGA 2007)
Information regarding the interaction of Backhousia with drugs, foods, or herbs is lacking.
When applied to the epidermal surface of human skin discs at exposure durations of 1 to 12 hours, 18.29 mg/cm2 of the essential oil resulted in reduction of cellular functioning, loss in integrity, loss of cellular vacuolation, cellular necrosis, and lower solubility of the stratum corneum. By comparison, when 0.18 mg/cm2 of the essential oil was applied to human skin discs for 8 hours' duration, the damage due to citral was limited to the epidermal cells.(Hayes 2002, Hayes 2003)
Cytotoxicity was found in vitro in the human cell lines HepG2 and F1-73 and primary cell cultures of human skin fibroblasts. Cytotoxicity 50% inhibitory concentration (IC50) values ranged from 0.008% to 0.014% (w/v) at 4 hours to 0.003% to 0.012% (w/v) at 24 hours of exposure. The no-observed-adverse-effect level for lemon myrtle oil was calculated as 0.5 mg/L at 24 hours' exposure, and the reference dose was determined to be 0.01 mg/L. A product containing 1% lemon myrtle oil was found to be low in toxicity and could therefore potentially be used in the formulation of topical antimicrobial products.(Hayes 2002)
As a topical product, the Australian CMEC recognizes the leaf oil of B. citriodora as safe and suitable for use as an active ingredient at a concentration not exceeding 1% w/w. Safety considerations are based on citral. The following issues regarding safety of B. citriodora should be considered: the existing exposure of the population to the active ingredient citral, given that it is widely used in the household, cosmetic, and food industries and the apparent lack of known adverse reactions associated with such exposure; the paucity of other important data regarding metabolism of citral, which might inform an assessment of the importance to humans of the physiological alterations induced by topical citral in rats; and topical administration of B. citriodora presented a potential risk, but that this risk was probably small. The committee recognized that additional data were needed to determine any safety risk posed by B. citriodora.(CMEC 2000)
The Australian TGA has approved B. citriodora oil derived from the leaf for topical use only. Concentration should not exceed 10 g/kg, 10 g/L, or 1%. Label statements are required that include warnings that B. citriodora is an irritant that should be used with caution in children and during pregnancy.(TGA 2007)
The majority of research has been conducted on citral as a common ingredient. Citral and citral oil are considered safe as 1% dilutions and have FDA GRAS status. When concentrated, citral-rich essential oils can be irritating to the skin.(Hegarty 2001)
This information relates to an herbal, vitamin, mineral or other dietary supplement. This product has not been reviewed by the FDA to determine whether it is safe or effective and is not subject to the quality standards and safety information collection standards that are applicable to most prescription drugs. This information should not be used to decide whether or not to take this product. This information does not endorse this product as safe, effective, or approved for treating any patient or health condition. This is only a brief summary of general information about this product. It does NOT include all information about the possible uses, directions, warnings, precautions, interactions, adverse effects, or risks that may apply to this product. This information is not specific medical advice and does not replace information you receive from your health care provider. You should talk with your health care provider for complete information about the risks and benefits of using this product.
This product may adversely interact with certain health and medical conditions, other prescription and over-the-counter drugs, foods, or other dietary supplements. This product may be unsafe when used before surgery or other medical procedures. It is important to fully inform your doctor about the herbal, vitamins, mineral or any other supplements you are taking before any kind of surgery or medical procedure. With the exception of certain products that are generally recognized as safe in normal quantities, including use of folic acid and prenatal vitamins during pregnancy, this product has not been sufficiently studied to determine whether it is safe to use during pregnancy or nursing or by persons younger than 2 years of age.
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