by Robert Tisserand

Essential-oil quality is important in aromatherapy, because substandard oils may contain ingredients that render the oil less effective or result in adverse skin reactions.

Yet, while it is widely accepted that aromatherapy—the use of essential oils to benefit health and well-being—can add benefits to massage, not many massage therapists know what determines the integrity of an essential oil.

Essential oils contain more than 100 individual, naturally occurring chemicals. Because they are plant-derived substances, there is a natural variation in composition, depending on such factors as where the plants are grown, soil composition, weather conditions, or time of day or year the plant is harvested.

For many essential oils, there are International Organization for Standardization standards in place, as well as pharmaceutical standards, that determine maximum and minimum ranges for certain key constituents in the oil.

Unfortunately, an oil may be adulterated, or manipulated, so that it conforms to standards. Therefore, such terms as pharmaceutical grade, therapeutic grade or food grade have no meaning in relation to the quality of essential oils for aromatherapy.

Quality, however, does depend on the following four areas: composition, oxidation, contamination and adulteration.

Composition: The amounts of specific chemicals present in a particular oil may make it more or less useful or desirable for aromatherapy purposes.

For example, a good-quality peppermint oil will be high in menthol (peppermint’s main active ingredient) and low in menthofuran and pulegone (both of which are slightly toxic). However, an oil that is not of good quality in this sense could still be derived from organically grown peppermint.

Oxidation: Many essential oils are prone to oxidation. This is a process in which some essential oil constituents combine with atmospheric oxygen to form breakdown chemicals—peroxides and hydroperoxides—many of which are skin allergens.

As an essential oil ages and oxidizes, it loses its therapeutic potency, because many of the active ingredients oxidize to quite different chemicals.

“Thinner” essential oils, such as citrus, pine and frankincense, are generally more likely to be oxidation-prone than viscous ones.

To avoid using oxidized essential oils: Replace bottle caps immediately after use; store essential oils in a refrigerator when not being used; do not leave essential oils near a source of heat or in direct sunlight; discard any essential oils that are more than 12 months old; and discard essential oils when there are only a few drops left in the bottle.

Contamination: Potential contaminants include antioxidants, herbicides and pesticides (collectively known as biocides), industrial solvents and phthalates.

Biocides are likely to be found in cold-pressed citrus oils from nonorganic fruit peel. They may also be found in nonorganic steam-distilled oils, though water-soluble biocides will probably not carry over into an essential oil. Simply because they are present in such small quantities (10 to 50 parts per billion), the amount of a biocide absorbed from aromatherapy is negligible compared to the amount ingested in nonorganic foods and beverages.

However, it will still contribute to biocidal body burden, and nonorganic citrus oils can contain pesticides at up to 50 parts per million. There is some evidence essential oils from organically grown plants are of better quality than those from nonorganic plants, but so little research has been carried out that it’s impossible to make any definitive statements.

Industrial solvents are used for the extraction of absolutes and resinoids. For example, there is no essential oil of benzoin (only a resinoid) and almost all jasmine “oil” is jasmine absolute. Rose absolute is also commonly used in aromatherapy, though there is an essential oil as well, known as rose otto. Solvents used include hexane and cyclohexane.

Most of the solvent used for extraction is recovered and reused, but traces do remain, at about 1 to 10 parts per million. Some people prefer not to use absolutes because of the solvents present in them, but these amounts are completely nontoxic, being several hundred times below minimal toxic levels.

There are a number of phlalate esters, commonly known as phthalates (the “ph” is silent), used in the manufacture of many plastics. They help make the plastic pliable. Since plastic tubing is used in citrus oil extraction, most cold-pressed citrus oils (organic or not) contain traces of phthalates. Manufacturers try to minimize phthalate quantities, which again are present at extremely low levels (about 1 part per million). Phthalates may also be artificially added to essential oils as adulterants, where they will be present in much higher concentrations.

Additionally, if an antioxidant has been added to a pure essential oil, this would technically be classified as a contaminant, since it is not a natural constituent of the oil. However, oxidation-prone essential oils will remain purer with an added antioxidant than without, since with no antioxidant, breakdown chemicals will form.

Adulteration: An adulterant is anything added to extend the genuine substance in order to increase profits. Adulterants include cheaper essential oils, synthetic aromachemicals, phthalates and other materials.

Most adulteration is not easy to identify from smelling an essential oil, but may show up in a gas chromatographic (GC) analysis. However, GC analysis is meaningless unless the person reading it knows what to look for.

There are many benefits of aromatherapy—and massage therapists who want to add aromatherapy to their practices must take the time to research essential-oil quality. Read labels and request information from aromatherapy companies. Make an effort to have a conversation with a representative of any company offering essential oils. Invest in high-quality aromatherapy products to achieve the best results for clients.

Robert Tisserand, MASSAGE MagazineRobert Tisserand is internationally acclaimed for his pioneering work and expertise in the practice of aromatherapy. He has been studying and promoting the benefits of essential oils since his first book on aromatherapy in 1977. Today he is actively involved in the formulation of Tisserand Aromatherapy’s personal-care products. For more information, visit