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

Luke Grocholl, Head of Regulatory

Sigma-Aldrich® Flavors & Fragrances

Essential oils bottles with herbs

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 before 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, which would eventually have an impact during the COVID-19 pandemic. Furthermore, Ebola prompted the FDA to establish some of its earliest policies and enforce stringent regulations regarding therapeutic claims associated with essential oils.

When the first Ebola cases were detected outside of sub-Saharan Africa in 2014, there was significant public concern. A US-based 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 fraudulent claims, the FDA issued several warning letters and began aggressively responding 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 mixtures of aroma chemicals and related compounds, such as terpenes and vegetable oils, extracted or physically isolated directly from botanicals. They may not actually be oily but often have a viscous, oily appearance or 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 distinguished primarily by extraction, isolation, and/or purification methods. This article 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

Steam distillation is the most commonly employed technique for extracting essential oils from botanicals. However, they can also be derived via such methods as solvent extraction or 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 processes like digestion, diffusion, or immersion of flowers to obtain pomades. The extracts and distillates may be isolated and 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 quality and characteristics. Similarly, essential oils inherently meet the definition of “natural raw material” in ISO 9235 and are often used for cosmetic or fragrance products so long as there are no synthetic additives in the essential oil. Because processing and purification methods for isolating essential oils sometimes result in the loss of some aroma chemicals, oils may sometimes be top-noted or base-noted by the addition other chemicals. Care should be taken when evaluating oils to determine if they have had any modifications or additions. Such materials may be synthetic, which then disqualifies the 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 the expected variations in 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 if the oil is properly labeled to indicate such additions. However, oils may also be intentionally adulterated to save costs. This type of deliberate contamination 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. When gas chromatography (GC) is utilized, it becomes possible to separate and analyze individual constituents of an oil. By combining it with mass spectroscopy (GCMS), analytical chemists have a powerful tool for detecting possible impurities within 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) can indicate if an oil has been diluted with synthetic materials. Sensory testing can also be used by experienced flavorists and perfumers to identify off-notes that may indicate poor quality or adulterated oils. A strong, reliable supply chain and a good relationship with the suppliers are two of the best methods to help address the risk of intentionally contaminated essential oils. Regardless of the controls in place, buyers should always be skeptical of essential oils offered below market price.

Watch for Allergens

Like all flavors and fragrances, allergens are a serious consideration when it comes to essential oils. Undeclared allergens remain a leading cause of food recalls, and fragrance allergens pose specific concerns with respect to essential oils. Hundreds of products in cosmetic and household categories have been flagged by IFRA (the International Fragrance Association, ifrafragrance.org). 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, the European Union prohibits the use of juniper oil (Juniperus sabina) in cosmetics, and within the EU, citral, which is present in lemongrass oil, lemon oil, basil oil, and similar oils, is recognized as a skin allergen. 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 threshold limits provided by regulations.

When the oils are used as food flavoring, there are considerably fewer hazards with respect to 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. As a result, highly refined oils are exempt from allergen labeling obligations. 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.

To help with your allergen testing, see our line of allergen certified reference materials.

Therapeutic Claims

In addition to flavor and fragrance applications, essential oils are sometimes promoted for therapeutic uses. Regulatory enforcement agencies consistently emphasize that any products with therapeutic claims are classified as drugs and must meet all the stringent requirements associated with their manufacturing, registering, and marketing. Therapeutic claims are defined as any assertion that a product can treat a disease or impact bodily functions. Claims such as aiding digestion, alleviating muscle soreness, or addressing depression all fall under the category of therapeutic claims. It is crucial to use precise language when making claims and to provide supporting evidence for those claims. For example, advertising that an essential oil aids in sleep constitutes a therapeutic claim, but statements promoting the conditions important for sleep may be considered acceptable. Claims that promote specific health benefits or the treatment of health conditions warrant thorough scrutiny, and it is advisable to consult regulatory authorities for clarification on such claims and their official position.

Summary

Essential oils are a valuable addition to any perfumer’s or flavorist’s toolbox, offering a wide range of intricate blends that create unique flavor and aroma experiences beyond what simple aromatic chemicals can achieve. However, it is crucial to have a comprehensive understanding of the potential risks associated with adulterated or mislabeled essential oils. The complexity of these ingredients can make it easier for bad actors to pass off inferior or hazardous substances as high-quality essential oils. Furthermore, great caution must be exercised before making therapeutic claims about essential oils, as only registered drug products are authorized to make such assertions. Regulatory agencies closely monitor false claims related to therapies and treatments. Being aware of the risks associated with essential oils enables formulators to use these important ingredients in the development of innovative and rich formulations for a demanding marketplace.

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References

1.
2015. IOFI GPS – Definitions of Forms.
2.
ISO 9235 Aromatic Natural Raw Materials – Vocabulary.
3.
Regulation (EC) No 1223/2009 of the European Parliament and of the Council of 30 November 2009 on cosmetic products.
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