Thyme (Thymus spp.) has been used for medicinal and culinary purposes for thousands of years. Of great interest today is its use as a natural antibiotic — or, more correctly, an antimicrobial. Growing evidence supports what aromatherapists have already been teaching: thyme essential oil, which is distilled from the leaves of the plant, has potent antibacterial, antifungal, and antiprotozoal properties.
About Thyme and Thyme Essential Oil
Thyme (genus Thymus) has multiple species. The most commonly used and known is Thymus vulgaris, or Common Thyme. It is also the most preferred variety for use in aromatherapy. According to Natural Standard, Thymus zygis (Spanish thyme) is often used in its place medicinally (Ulbricht & Basch).
According to King’s American Dispensatory (1999-2010), the pungent, spicy smell and taste of the herb is due to its volatile oil content. When extracted from the leaves, this essential oil of thyme is known as red thyme. It is very strong and has harsh, irritating properties. When rectified (distilled), it becomes white thyme, a milder essential oil.
Be aware that red and white thyme essential oils can be made from different species of thyme, and that each has separate properties. Always check for the Latin name of the plant, which should appear on the bottle of oil (usually below the common name). Unless you are looking for another specific species, use Thymus vulgaris.
It is typical for thyme plants of the same species to produce essential oils that are made up of different, unique combinations of chemicals. (For the sake of this article, “chemical” automatically means “natural chemical.”) This means that two T. vulgaris plants can produce essential oils with distinct chemical makeups, properties, and therapeutic effects. These are called chemotypes.
(As you can imagine, this makes choosing the correct thyme essential oil even harder! Not only do you have to choose the right species and color of thyme oil that you want to use, you need to check that you have the chemotype you want, too!)
At least four chemotypes of thyme have been recognized, and they are named according to which component is most abundant in the essential oil. For instance, a plant of the thymol chemotype produces an essential oil that is primarily made up of the chemical thymol.
Four chemotypes of thyme oil are thymol, thujanol, linalol, and geraniol (Keville & Green,; Schnaubelt, 1995). According to Keville and Green, geraniol and linalol are gentler, thymol is very irritating and very antibacterial, and thujanol is good against viral infections.
A series of studies in the late 1970s and 1980s tested the antibacterial properties of six different chemotypes: geraniol, linalol, terpineol, thujanol, carvacrol, and thymol. A review published in 1987 compared the chemotypes and showed that, while all six were effective antibacterials, some were more effective against certain bacteria than others (Jansen, Scheffer, & Baerheim-Svendsen). Only one chemotype was very effective against all bacteria tested, and that was the thymol chemotype.
Schnaubelt (1995) states that most thymol type oil is produced from the species Thymus zygis. However, according to him, thymol-type T. vulgaris is better, because its oil is purported to have a broader spectrum against microbes and a more pleasing scent.
Antibacterial and Antifungal Properties of Thyme
Multiple recent studies suggest that thyme essential oil does, indeed, have significant antimicrobial properties.
According to one study, the antimicrobial effects of thyme oil appear to be additive; that is, they are due to several compounds working together (Iten, Saller, Abel, & Reichling). Thymol, carvacrol, and linalol appeared to be the active antimicrobial components. The researchers proposed that the complex, additive components of thyme oil (which can change from year to year and lot to lot) may make thyme oil more stable than preparations with only one active component (like pharmaceuticals).
Here are short summaries of the most applicable research results. (Note: of all the studies reviewed, including those not summarized here, every one concluded that thyme oil was an effective antibacterial.)
- Carvacrol-type thyme oil inhibited H. pylori (bacteria in the stomach that can produce stomach ulcers) (Eftekhar, Nariman, Yousefzadi, Hadiand, & Ebrahimi).
- Thyme oil was effective against a fungus that causes citrus fruit sour rot (Liu, Wang, Li, Li, Yu, & Zheng). The researchers suggested it can possibly replace commercial agricultural sprays that are currently used to treat the trees.
- Two chemotypes of thyme oil were found to be significantly effective against Staphylococcus aureus, E. coli, and Pseudomonas (Talei & Meshkatalsadat,).
- Thyme oil was effective against Entamoeba histolytica (a protozoan parasite) (Behnia, Haghighi, Komeylizadeh, Tabaei, & Abadi).
- The essential oil of two different species of thyme were both found more effective at killing fungi than a commercial fungicide, bifonazole (Sokovic, Vukojevic, Marin, Brkic, Vajs, & van Griensven, L.).
- A 1% solution of T. vulgaris appeared effective against three fungal skin infections produced by Trichophyton spp. (Sokovic, Glamoclija, Ciric, Kataranovski, Marin, Vukojevic, & Brkic). (A 1% solution is a typical, safe dilution used in aromatherapy, according to Keville and Green.)
Thyme Essential Oil Warnings
Thyme essential oil is highly irritating to the skin and mucous membranes. It is considered highly toxic.
According to Natural Standard, thyme should be avoided by anyone with an allergy to the mint family or to rosemary. Also, the authors state that thyme may decrease levels of thyroid hormone.