Lemon Myrtle

Generic name: Backhousia Citriodora F. Muell.
Brand names: Lemon Myrtle, Sweet Verbena Myrtle

Usage of Lemon Myrtle

Citral has sedative, antiviral, and antifungal properties. Although not clinically proven, citral is also considered to have antitumor properties.(Pengelly 1991)

Antibacterial/Antifungal/Antiviral activity

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)

Clinical data

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)

Anti-inflammatory effects

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)

Antioxidant effects

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)

Sarcopenia

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)

Tick repellent

Animal data

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)

Before taking Lemon Myrtle

Information regarding safety and efficacy in pregnancy and lactation is lacking. Caution is warranted with topical B. citriodora oil use during pregnancy.(TGA 2007)

How to use Lemon Myrtle

Clinical trial data are lacking to provide dosing recommendations.

Warnings

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)

What other drugs will affect Lemon Myrtle

Information regarding the interaction of Backhousia with drugs, foods, or herbs is lacking.

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