Lavender essential oil: a review

Lavender essential oil is popular as a complementary medicine in its own right and as an additive to many over the counter complementary medicine and cosmetic products ' \ Indeed, products derived from the popular garden herb Lavender (Lavandula spp.) have been used for centuries as a therapeutic agent, with the more 'recent ' addition, the essential oils derived from these plants, being widely used as an antibacterial in World War I],! The oil is traditionally believed to have sedative, carminative, anti-depressive and antiinflammatory properties, in addition to its recognised antimicrobial effects. Many of the activities attributed to lavender oil have not, however, been substantiated in the scientific literature. This is further complicated by the fact that the majority of research into lavender essential oils has been based on oil derived from English lavender (Lavandula angustifolia), with little or no differentiation being made between this and other lavender essential oils. The therapeutic potential of essential oils produced from other varieties, such as L. x intermedia (lavandin), L. stoechas (French lavender) and L. x allardii, have largely been ignored. Although the ethnobotanical uses and major chemical constituents are similar between various lavenders, some differences do occur in both oil composition and in the reported therapeutic uses for different ~ p e c i e s ~ , ~ . The significant scientific interest in recent years into the validity/veracity of the traditional beliefs surrounding lavender oil and their scientific basis, if any, was recently reviewed by Cavanagh & Wilkinson? In this paper we provide an overview of the use of lavender oil in infectious disease and an update on recent research on alternative uses of lavender oil. Lavender oil (primarily L. angustifolia) has been found to be active against many species of bacteria, including those resistant to antibiotics such as methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococcus (VRE) b~R. Recent investigations into the antibacterial properties of a range of Lavandula oils (L. angustifolia, L. allardii, L. x intermedia 'Grosso', L. x intermedia 'Seal', L. x intermedia 'Miss Donnington', L. x heterophylla and L. stoechas 'Avonview') support the anecdotal use of lavender oils as antibacterial agents and demonstrated that Despite the known antibacterial activity, questions remain about the clinical utility of lavender oil. The MIC (minimum inhibitory concentration) values of lavender oil (L. angustifolia and L. latifolia) have been reported as being comparable to that of tea tree oil (0.16% against Haemophilus influenzae, 0.32% against S. pyogenes and S. aureus and greater than 0.32% against E. ~ o l i ) ' ~ . These figures would appear to support the use of lavender oils as a prophylactic or for use in topical application for surface infection rather than for use against deep-seated infections. some oils which had previously not been investigated (e.g. L. Lavender oil has also been reported to be an effective antifungal heterophylla) displayed good antibacterial activity against a range agent against fungi of both medical and agricultural importance, of bacteria including Streptococcus pyogenes, Enterobacter aerogenes, especially in inhibition of germ-tube growth ". A recent study S. aureus, MRSA, Pseudomonas aeruginosa, Citrobacter freundii, demonstrated that all Lavandula essential oils examined to date Proteus vulgaris, Escherichia coli, VRE, Shigella sonnei and displayed some antifungal activity, with oils derived from L. Propionibacterium acnes 9. an~ustifolia and L. x intermedia demonstrating the greatest effect . Interestingly, there was considerable variability in the activity of against Aspergillus nidulans and Trichophyton mentagrophytes. the essential oils, with L. angustifolia and L. x intermedia oils In contrast, oil derived from L, stoechas was particularly effective showing the highest activity against several bacteria. However, against the agricultural fungi Leptosphaeria maculans and Sclerotinia no one oil produced the highest level of antibacterial activity sclerotiorum, demonstrating that Lavandula oils have activity against all bacteria tested, suggesting that differences in chemical against fungi of both medical and agricultural importance, and composition make some oils more effective against particular suggesting that essential oils from various lavender varieties may bacteria. No strong correlation has been observed between be useful in the treatment of fungal infections ''. percentage of major chemical components and antibacterial activity, and P aeruginosa was not susceptible to any Lavandula oil The recent interest in the therapeutic use of hydrosols, however, tested9. These results support the anecdotal use of lavender oils appears unlikely to have scientific merit as no antimicrobial as antibacterial agents and demonstrate that some oils which had activity has been found to be associated with any Lavandtlla previously not been investigated have good antibacterial activity. hydrosols examined by this group to date 12. Hydrosols or Vol10 Issue 1 March 2005 Australian Infection Control distillate waters are a by-product of steam distillation and contain variable amounts of essential oil and other plant derived components. The variation found in the activity of the different oils suggests that different oils should be targeted for different therapeutic uses. Further work is required to determine whether the in uitro results are realised in a clinical environment, but it is clear that not all lavenders are equal in terms of their antimicrobial properties. Interestingly, the volatile components of Lavandula essential oils have also been found to display potent antifungal activity; however, no significant differences in activity have been reported between different Lauandula oil volatiles l 2 I 5 . Vapour treatment would appear to have an advantage over solution treatment in that the microbial growth could be inhibited by a smaller amount of essential oil, while potentially also acting as a potent inhibitor of sporulation, assuming that suitable vapour concentration and treatment times can be determined. Initial studies suggest that the gaseous contact activity of the essential oils was determined mainly by the maximum vapour concentration at an early stage of incubation and that maintaining high vapour concentration for long periods of time was not necessary 15. It should be noted, however, that the effective vapour concentrations in a clinical setting have not yet been directly related to the concentrations used routinely in aromatherapy. The use of essential oil volatiles for therapeutic benefit is not new. Indeed, lavender oil today is used predominantly in aromatherapy or massage, and many benefits are claimed for its use in this way, including relief of the symptoms of stress and depression, in improving 'mood' and relieving anxiety 3. Aromatherapy is thought to be therapeutically effective due to both the psychological effect of the odour and the physiological effects of the inhaled volatile compounds, where the latter effects are believed to act via the limbic system, particularly the amygdala and hippocampus. However, although inhalation of lavender oil volatiles has been reported to be capable of altering patient mood and improving sleep patterns, the true therapeutic benefit of inhalation of lavender oil remains controversial ', 16, 17. This may be related to the fact that many studies combine both massage and lavender oil and are unable to determine whether the benefits seen are as a result of massage or of lavender oil inhalation/absorption. For example, a recent study investigating the use of lavender oil aromatherapy in dementia patients found no evidence that a purely olfactory form of aromatherapy led to decreased agitation in severely demented patients and suggested that cutaneous application of the essential oil may be necessary to achieve the optimum effect 18. Similarly, although percutaneous administration of one of the main ingredients of lavender oil, (-)linalool, led to a decrease in systolic blood pressure and skin temperature, compared to a corresponding control group receiving a placebo, no effect on subjective evaluation of wellbeing was noted 19. In another study, although massages with lavender essential oil and an inert carrier oil were unable to demonstrate any significant long-term benefits in improving pain control, but anxiety or quality of life (compared to those patients who received the inert carrier oil only or no massage) and sleep scores improved significantly in both the massage and the combined massage (aromatherapy and massage) groups. These findings were accompanied by a statistically significant reduction in depression scores in the massage group, whether lavender oil was used or not 20. Inhalation of lavender aromatherapy during radiotherapy was also found to reduce anxiety 21. Conversely, several authors have noted an association between lavender odour, positive emotional states and therapeutic benefit 22~25. For example, Diego et al. 26 found that individuals receiving lavender oil (10%) odour for 3 minutes were significantly more relaxed, had decreased anxiety scores, better moods and showed increased alpha power in their EEGs (an indication of increased drowsiness). Similarly, in a pilot study by Walsh & Wilson 27, long-stay neurology in-patients also showed increased mood scores and reduced psychological distress following aromatherapy (tea tree, rosemary and L. angustifolia oils), suggesting that lavender aromatherapy can improve patients' experiences in intensive care with no detrimental physical or behavioural outcomes. Inhalation of lavender oil is also reported to be of benefit in pain relief. Lavender oil has been shown to be an effective short-term treatment for lower back pain when acupoint stimulation was followed by acup