Abstract
The topical use of essential oils requires dilution into a carrier oil; however, scientific evidence regarding the antimicrobial efficacy and cytotoxicity when a carrier oil is combined with an essential oil is lacking. This study sets out to determine the antimicrobial activity and cytotoxicity of 23 essential oils combined with six known carrier oils. Gas chromatography-mass spectrometry/flame ionization detector (GC-MS/FID) was used to characterize the methyl esters of the carrier oils. The antimicrobial activity of the carrier oils alone and in combination with the essential oils was investigated using the broth microdilution assay against 11 skin pathogens and the cytotoxicity was determined using the brine shrimp lethality assay. The interactive profiles of the combinations for both antimicrobial activity and the cytotoxicity were analysed and calculated using the fractional inhibitory concentration index (ΣFIC). The carrier oils demonstrated no antimicrobial antagonism when combined with the essential oils and the overall cytotoxicity of the majority of the combinations was decreased. The carrier oils that could be identified as enhancing the antimicrobial activity and decreasing the cytotoxicity were Aloe vera Mill. and Simmondsia chinensis C.K.Schneid (Jojoba oil), with an overall reduction in essential oil cytotoxicity of 87.5% at 24 hrs and 85% at 48 hrs by A. vera. Five of the essential oils (when diluted in A. vera and S. chinensis carrier oils) demonstrated enhanced antimicrobial activity against pathogens such as Brevibacterium epidermidis, B. linens, and P. aeruginosa with MIC values ranging from 0.09 to 0.50 mg/mL (and ΣFIC 0.14-0.39). The study could conclude that the carrier oils are complementary to essential oil formulations, mostly reducing cytotoxicity and in some cases enhancing the antimicrobial activity.
Highlights
Essential oils are popular in complementary medicine and often used to treat dermatological conditions
There is a paucity of information relating to the effects of carrier oils on the antimicrobial activity and cytotoxicity of essential oils [7]; this study investigates this void with special emphasis on oils implicated in dermatology and interactions affecting skin pathogens
The selection of six carrier oils was based on the aroma-therapeutic literature available to the layman as reviewed by Orchard and van Vuuren [7], where the most frequently cited carrier oils for dermatological use and those claimed as having antimicrobial activity were selected
Summary
Essential oils are popular in complementary medicine and often used to treat dermatological conditions. (tea tree), which is known worldwide as an anti-infective essential oil and is used in many commercial acne products These products are considered as a “safe” alternative and a preferred holistic treatment by consumers, but what has not been considered is the common use with a carrier oil. Possible bases that essential oils can be diluted into include creams, gels, or carrier oils ( known as vegetable or fixed oils) [5]. It has, been found that a base can influence the overall antimicrobial activity of the oil [6]. There is a paucity of information relating to the effects of carrier oils on the antimicrobial activity and cytotoxicity of essential oils [7]; this study investigates this void with special emphasis on oils implicated in dermatology and interactions affecting skin pathogens
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