Essential Oils: What to Watch for in These Complex Natural Extracts

A Dangerous Outbreak, Suspicious Claims, and The Regulatory Response

In late June 2014, a worker in a cotton factory in Sudan was hospitalized with severe diarrhea and dehydration. The patient died within a week and was unfortunately the first victim of an unknown disease. The subsequent outbreak killed over 150 people and sickened almost 300, some with severe symptoms that included internal, and even external bleeding such as bleeding through the tear ducts. It would be months until the virus responsible for this disease was identified and named. The world had experienced its first Ebola outbreak. This horrible disease would help shape global health policies, such as travel bans and screenings, that would eventually have an impact during the COVID-19 pandemic. Ebola would also lead the FDA to some of the first policies and strong enforcement on essential oil therapeutic claims.

When the first Ebola cases were detected outside of sub-Saharan Africa in 2014, there was significant public concern. A US-base aromatherapy company began marketing some of their products with claims they could be used to treat Ebola as well as other conditions such as cancer, infections, and brain injuries. Prompted by concerns over fake cures and false claims. The FDA issued several warning letters and began responding aggressively to firms that made therapeutic claims without the proper evidential support and regulatory filings. Much of the regulatory enforcement of essential oils involves health claims, but there is still confusion over how to define and market essential oils for all applications.

What is an Essential Oil?

Essential oils are the mixtures of aroma chemicals and related compounds such as terpenes and vegetable oils extracted or physically isolated directly from botanicals. They may not be oily, but often have a viscous oily-like appearance. They could even be waxy solids or resins. IOFI (the International Organization of the Flavor Industry, iofi.org) and ISO (the International Organization for Standardization, iso.org) both offer similar definitions of essential oils and related complex, aromatic, botanically derived ingredients.^1,2 The IOFI and ISO documents define many types of botanically derived, aromatic mixtures distinguished primarily by extraction, isolation, and/or purification methods. For the sake of this article, I will not differentiate between such forms as gums, waxes, resins, and essential oils but will use the term essential oil as a generic term for all direct botanical extracts.

Manufacturing Methods

The most common method for extracting essential oils from botanicals is steam distillation, but they can be obtained through solvent extraction or even by expression using physical presses. Some essential oils can be obtained through other highly specialized methods, such as slow-folding methods for extracting citrus oils known as sfumatura (from the Italian for softening or blurring indicating the soft, slow method) or digestion, diffusion, or immersion of flowers to obtain pomades. The extracts and distillates may be isolated ready-to-use or may require further purification ranging from simple decanting to fractional distillation. Regardless of the manufacturing method, the end-product is a complex mixture of aroma chemicals and related compounds.

Natural Declarations and Verification

Since these methods all involve physical separation of the aroma chemicals from their botanical sources, essential oils meet regulatory and other definitions of natural flavors. Essential oils, when used as flavoring, can be labeled as a natural flavor in the US, EU, and most other global regions, but some caution should be taken when evaluating the flavoring. Similarly, essential oils inherently meet the definition of “natural raw material” in ISO 9235, often used for cosmetic or fragrance products so long as there are no synthetic additives in the essential oil. Processing and purification methods for isolating essential oils sometimes result in the loss of some aroma chemicals. Oils may therefore sometimes be top-noted or base-noted by the addition of aroma chemicals. Care should be taken when evaluating oils to determine if they have had any modifications or additions. Such material may be synthetic flavors which then disqualifies natural claims associated with the essential oil.

Natural verification of essential oils can be difficult. Since they are complex mixtures, it is often difficult to analytically identify a single component that could be added. Furthering the complexity are expected variations of the composition of the natural oil itself. Botanical crop quality is subject to regional and seasonal variations which may impact the composition of the oil. Extraction, purification, and storage methods also impact essential oil quality and composition.

Confirming Quality

Addition of top or base notes to oils may be fully legitimate as long as the oil is properly labeled to indicate such additions. However, oils may also be intentionally adulterated to save costs. This type of intentional adulteration for economic purposes includes diluting the oil with other cheaper oils, or even synthetic mineral oil. Fortunately, careful analytical testing can often detect adulteration. Essential oils have distinct “fingerprints” detected by different chromatographic tests. Gas chromatography (GC) can separate and characterize each component of an oil and when coupled with mass spectroscopy (GCMS), analytical chemists have a powerful tool to identify potential adulterants in essential oils. Some simple methods, such as viscosity or specific gravity analysis can also identify adulteration such as dilution. Naturalness verification by carbon-14 ratio (¹⁴C) will indicate if an oil has been diluted with synthetic materials. Sensory testing can also be used by experienced flavorists and perfumers who can identify off-notes that may indicate poor quality or adulterated oils. A strong reliable supply chain and a good relationship with the suppliers is one of the best methods to help address the risk of intentionally adulterated essential oils. Regardless of the controls in place, buyers should always be skeptical of essential oils offered below market price.

Watch for Allergens

As with all flavors and fragrances, allergens can be a concern for essential oils. Undeclared allergens continue to be one of the primary reasons for food recalls and fragrance allergens are of particular concern for essential oils. IFRA (the International Fragrance Association, ifrafragrance.org) has identified hundreds of products of concern in cosmetic and household products. The EU has a similarly extensive list in its regulations on cosmetics.³ Some essential oils are specifically identified as skin irritants, whereas others could contain components on the EU and/or IFRA prohibited or restricted lists. For example, juniper oil (Juniperus sabina) is prohibited for use in cosmetics in the EU and citral, a constituent of lemon grass oil as well as lemon oil, basil oil, and related oils is a known skin allergen in the EU. Therefore, juniper oil should not be used in cosmetic applications, and where citral-containing oils are used, care should be taken to ensure the citral levels are below the thresholds of concern provided by the regulations.

When the oils are used as food flavoring, there is considerably less concern from potential allergens. The US FDA, the EU, and many other regulatory bodies recognize that highly refined oils are free or nearly free of the proteins that could cause food allergies. Highly refined oils are therefore exempted from allergen labeling requirements. Nevertheless, it is recommended that flavor producers disclose to their customers any essential oils derived from major food allergens. Food companies often require a full list of products they receive that could be derived from a major food allergen.

Therapeutic Claims

In addition to flavor and fragrance applications, essential oils are sometimes promoted for therapeutic uses. Regulatory enforcement agencies are consistent that any products with therapeutic claims are drugs and must meet all the stringent requirements associated with manufacturing, registering, and marketing of a drug. Therapeutic claims are defined as any claim the product would treat a disease or affect the function of the body. Claims such as digestive relief, reduction of muscle soreness, or treating depression are all therapeutic claims. Proper wording of any claim and evidence for those claims is important. For example, a claim that an essential oil will help a person sleep is a therapeutic claim, but statements promoting the conditions important for sleep may be acceptable. Any claims promoting specific health benefits or treatment of health conditions should be carefully reviewed, and it is recommended that any questions on such claims be brought to regulatory authorities to understand their position.

Summary

Essential oils are a wonderful addition to any perfumer or flavorist’s toolbox. These complex mixtures provide flavor and odor sensations not realized by simple aromatic chemicals. However, a thorough understanding of the potential risks from adulterated or mislabeled essential oils is important. The complex nature of these ingredients may make it easier for bad players to try and pass off inferior or even dangerous ingredients as high-quality essential oils. Extreme care must also be taken before promoting beneficial claims from essential oils. Only registered drug products can make therapeutic claims and regulatory agencies monitor false claims related to therapies and treatments. Knowing the risks associated with essential oils allows formulators to use these important ingredients to develop new and rich formulations for a demanding marketplace.

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