What Are Essential Oils?
Essential oils are aromatic volatile oils produced by medicinal plants that give them their distinct flavors and aromas. They are extracted using a variety of different techniques, such as microwave-assisted extraction, headspace extraction, and the most commonly employed hydrodistillation.1 Different parts of the plant are used for the specific oils; the shoots and leaves of Origanum vulgare are used for oregano oil, whereas the skins of Citrus limonum are used for lemon oil.2 Historically, essential oils have been used for cooking, food preservation, perfume, and medicine.3,4
Historical Uses for Essential Oils
Essential oils and their intact medicinal plants were among the first medicines widely available to the ancient world. The Ancient Greeks used topical and oral oregano as a cure-all for ailments including wounds, sore muscles, and diarrhea. Because of its use as a cure-all medicine, it remains a popular folk remedy in parts of Europe today.3 Lavender also has a long history of being a cure-all plant and oil. Some of the many claims behind this flower include treatment of burns, insect bites, parasites, muscle spasms, nausea, and anxiety/depression.5 With an extensive list of historical uses, many essential oils are being researched to determine if their acclaimed qualities have quantifiable properties.
Science Behind the Belief
In vitro experiments with oregano (O vulgare) have demonstrated notable antifungal and antimicrobial effects.6 Gas chromatographic analysis of the oil shows much of it is composed of phenolic monoterpenes, such as thymol and carvacrol. They exhibit strong antifungal effects with a slightly stronger effect on the dermatophyte Trichophyton rubrum over other yeast species such as Candida.7,8 The full effect of the monoterpenes on fungi is not completely understood, but early data show it has a strong affinity for the ergosterol used in the cell-wall synthesis. Other effects demonstrated in in vitro studies include the ability to block drug efflux pumps, biofilm formation, cellular communication among bacteria, and mycotoxin production.9
A double-blind, randomized trial by Akhondzadeh et al10 demonstrated lavender (Lavandula officinalis) to have a mild antidepressant quality but a noticeably more potent effect when combined with imipramine. The effects of the lavender with imipramine were stronger and provided earlier improvement than imipramine alone for treatment of mild to moderate depression. The team concluded that lavender may be an effective adjunct therapy in treating depression.10
In a study by Mori et al,11 full-thickness circular wounds were made in rats and treated with either lavender oil (L officinalis), nothing, or a control oil. With the lavender oil being at only 1% solution, the wounds treated with lavender oil demonstrated earlier closure than the other 2 groups of wounds, where no major difference was noted. On cellular analysis, it was seen that the lavender had increased the rate of granulation as well as expression of types I and III collagen. The most striking result was the large expression of transforming growth factor β seen in the lavender group compared to the others. The final thoughts on this experiment were that lavender may provide new approaches to wound care in the future.11