Here is a list of frequently asked questions with answers.

What is an essential oil?

An essential oil is a highly condensed form of plant matter extracted from special secretory glands within the plant that could be located in various parts such as the petals, fruits, leaves, wood, or roots. These secondary metabolites are produced by the plant for various reasons such as to detract insects and herbivores, to protect from disease, or to reduce the growth of other plants nearby. Not all plants produce essential oils, and some produce oils that can be very toxic, like sassafras (Sassafras spp.), pennyroyal (Mentha pulgium), and thuja (Thuja occidentalis).  Essential oils are extracted, in the majority of incidences, by steam distillation, in which only the highly volatile constituents with a molecular weight under 250 are kept, leaving all of the heavier components and plant matter behind, and typically only representing about 1% of the plant. Thus, an essential oil’s chemistry can be quite different than that of the overall herb.

What is aromatherapy?

Aromatherapy is the use of essential oils for aromatic pleasure as well as physical and mental well being.

What is an herb?

An herb is a plant used in phytotherapy to prevent and treat disease. Herbal drugs can be gentle or very powerful, depending upon their chemical components. They can be used to treat whole body wellness, or a specific symptom, and, like drugs, they have a therapeutic margin, contraindications, drug interactions, and potentially undesirable side effects. According to Weiss and Fintelmann,1 herbs with very potent active constituents also run the risk of having greater side effects, and it’s important to stay within the guidelines of the maximum permissible dose (amount in one dose, number of doses per day, and for the amount of duration) based on weight, age, and overall health.

What is the difference between an herb and a steam distilled essential oil?

Steam distillation is a method of extracting just the essential oils from a plant. Steam distillation only extracts compounds with a maximum molecular weight of 225 – 250.2 Thus, the essential oil from a plant will have a significantly different chemical composition than an herb preparation of a plant because only the volatile chemical constituents are extracted. Typically, this represents 2% or less of a plant’s total matter. An estimated percent yield for basil (Ocimum basilicum) is 0.5 – 1.5%, cedarwood (Cedrus atlantica) is 4.5%, eucalyptus (Eucalyptus globulus) is 1.0 – 7.0%, and rose (Rosa x damascena) is 0.006%. According to Clarke, 2 it would take about 4000 pounds of rose petals to produce one pound of essential oil! Thus, essential oils only contain the light weight chemical constituents, including terpenes (monoterpenes, sesquiterpenes, and sometimes diterpenes) and oxygenated compounds: Alcohols, aldehydes, ketones, acids, esters, phenols, ethers, lactones, and oxides.

Furthermore, some chemistry can change with the distillation process, when constituents become hydrolyzed by the hot water. An example is the linalyl acetate ester in lavender (Lavandula angustifolia) breaking down into linalool and acetic acid.2 Another example: During steam distillation, the matricin component in German chamomile (Matricaria recutita) decomposes to chamazulene.2 Essential oils are made up of multiple chemical constituents, and the quantity of each constituent can vary based on the quality and chemotype of plant matter used, conditions associated with the distillation process, and possible dilution and adulterations made to an oil.

When using essential oils, there tends to be a much smaller therapeutic margin than when using the whole herb, and it is important to be aware of key constituents in each oil, thus knowing the therapeutic benefits and also possible toxicity and contraindications. In addition, when making recipes and using oils, realize that all essential oils are volatile, meaning that they evaporate easily, and are hydrophobic; meaning that they are fat soluble so they dissolve easily into oil based ingredients, and not well in water based ingredients.

What is a contra-indication?

A contra-indication is a medical condition in which a certain remedy is less safe to use.  For example, cinnamon essential oil is contra-indicated with young children, pregnant women, pets, and certain health conditions.

What is a therapeutic margin?

With intake of any medicine or herb, there is an amount needed to be effective, and an amount that is too much, and unsafe.  Therapeutic margin is the ratio between the amount that is determined as safe and the amount that is determined as toxic.

What is a chemical constituent?

These are the chemical components that make up a plant material.  Each plant, and the way it is prepared will render differing chemical compounds.  Some chemical compounds can be a major contributor to aroma, flavor, therapeutic actions, and contra-indications.  Collectively, it is all the chemical components of an herbal preparation that make it synergistically special.

What is a botanical or scientific name?

Botanical names identify a specific plant and usually originate from Latin or Greek words.  This can be helpful when a plant has multiple common names across multiple countries.  Most commonly, the genus and species are listed in a botanical name, and are usually written in an italics font.  Sometimes, subspecies or chemotype may also be included at the end of the name, and is not written in italics font.  For research purposes, it is important to use botanical names to accurately identify the plant being studied.


  1. Weiss, R. & Fintelmann, V.  (2000). Herbal Medicine.  Second Edition. Revised and Expanded.  Thieme. Stuttgart.
  2. Clarke, S. (2008). Essential chemistry for safe Aromatherapy. Edinburgh: Churchill Livingstone.