Same Botanical Name. Different Aromatic: Understanding Essential Oil Quality

Originally published: [June 2025] Updated September 2026: This article has been updated with additional information on chemotypes, natural aromatic variation, essential oil quality assessment, and the naturopathic and functional medicine perspective on individualized essential oil selection.

 

Article Summary

How do you know if an essential oil is truly high quality?

Essential oil quality is more complex than a label claim such as “pure” or “therapeutic grade.” The botanical species, chemotype, growing conditions, harvesting, distillation, storage, sourcing, and manufacturing practices can all influence an oil’s chemical and aromatic profile.

This article explores how to evaluate essential oil quality from the plant source to the finished product, including verification testing, GC/MS analysis, Certificates of Analysis, natural chemical variation, and the limitations of relying on any single quality measure.

I also discuss why the same botanical can produce different aromatic profiles and how a naturopathic and functional medicine perspective considers not only the oil’s chemistry and quality, but also the individual, their physiology, health history, goals, and intended application.

Quality requires more than a label. It requires discernment.

 

Table of Contents

• Finding Quality Essential Oils
• My Initial Search for Quality Essential Oils
• Understanding Natural Variation in Essential Oils
• Understanding Chemotypes
• Ensuring Quality Control from Start to Finish
• Verification Testing for Essential Oil Quality
• Certificates of Analysis and GC/MS
• Understanding the Limitations of GC/MS
• Safe Application of Essential Oils
• A Naturopathic and Functional Medicine Perspective
• Aromatic Personalization
• Summary: Evaluating Essential Oil Quality
• Resources
• Frequently Asked Questions

 

Finding “Quality Essential Oils”

Finding high-quality essential oils can be challenging due to varying opinions on preferred brands and the absence of a single comprehensive governmental regulatory standard defining essential-oil quality and purity for aromatherapy. As a result, I have compiled a series of articles to help clarify this confusion for both new and experienced users.

Part I reviewed:

• The various factors that impact the selection of essential oil brands, including individual values, company reputation, price, community engagement, and marketing strategies.
• My goal to remain brand neutral and focus on the scientific aspects of essential oils to reach a broader audience, without the distraction of selling, marketing, or introducing biases.
• Research on essential oils aims to investigate and, in some cases, standardize or characterize compounds based on their biological properties, yet it offers limited details regarding their quality and purity.

Part 2 covered the standards and regulations of essential oils. Key points included:

• Essential oils’ composition, quality, and safety can be affected by their production, manufacturing, and distribution.
• In the U.S., essential oils are not subject to a single federal standard for quality or purity as aromatherapy products; however, products are subject to applicable FDA requirements depending on their intended use, claims, labeling, and marketing.
• Standards set by key global organizations (ISO and AFNOR) provide specifications for the identity and chemical characteristics of particular essential oils.
• Meeting a standard or specification does not, by itself, establish overall quality or guarantee the absence of adulteration.
• High quality or pure essential oils may not meet consensus standards for specific compounds because natural chemical variation, including chemotypes, can occur within a botanical species.

In this final installment, Part III, I take a closer look at how I evaluate essential oil quality in practice—from the plant source and production process through verification testing, Certificates of Analysis, chemical composition, and safe application. I also explore why natural chemical variation, including chemotypes, matters when evaluating an essential oil and why a naturopathic and functional medicine approach considers the individual alongside the oil itself.

 

My Initial Search for Quality Essential Oils

When I first began my essential oils journey, I was very skeptical. At the time I was a pharmacy technician, and I was very wary of my mom’s “unregulated hippie herbs” and “plant juices.”

Wanting to discover if what she was touting and the “internet hype” was founded, I became curious and started researching. One of my first discoveries was the book, “The First International Symposium on Integrated Medical Aromatherapy in Grasse, France (March 21-22, 1998).”

This book contained various presentations from who I now understand to be impressive and esteemed essential oil experts. These included Pierre Franchomme and Daniel Penoel, M.D. It also discussed various quality control measures, including using certificates of analysis. These were one way to provide evidence of important constituents found in specific essential oils.

Other highlights within this text included:

• The complexity of determining the quality of an oil vs. identifying its compounds using gas chromatography
• Volatile contaminants have been found in essential oils from poor manufacturing
• Benzene (a potential carcinogenic compound) and contact allergens were present in various fragrances
• The chemical composition of essential oils varies with seasons, cropping type, location, and climate
• How topsoil affects components of essential oils

I was then given an opportunity to visit a premier company’s essential oil supplier’s farm, which I’ve since recently returned to. Based on my book knowledge, I was impressed with their organic farming, production, and their passion for purity.

This provided me with confidence that these oils were of high quality, prompting me to incorporate them into my clinic and for personal use. Later, I discovered I still had more aspects to consider regarding essential oil purity. Thankfully, the same producer fulfilled these as well as few others.

 

Understanding Natural Variation in Essential Oils

The same botanical name does not always mean an essential oil will have an identical chemical or aromatic profile. Natural variation can occur within a plant species due to genetics, growing location, climate, soil, season, plant maturity, harvesting conditions, and extraction methods. These factors can influence the relative proportions of constituents and, consequently, the aroma and other characteristics of the resulting essential oil. Natural variation is not necessarily an indication of poor quality or adulteration.

This is one reason quality assessment requires context. A difference in chemical composition does not automatically mean one oil is better or worse; it may reflect the natural biology of the plant and how it was grown, harvested, and processed.

 

Understanding Chemotypes

A chemotype is a chemically distinct variation within the same botanical species. Plants can share the same botanical name and physical characteristics while producing essential oils with different predominant chemical profiles. These differences may be influenced by genetics and can interact with environmental and growing conditions. Importantly, not every difference in an essential oil represents a chemotype; a true chemotype reflects a recurring and relatively stable chemical pattern rather than a temporary change caused by season, location, harvest, or processing.

This distinction matters when evaluating essential oils because different chemotypes of the same botanical may have different aromas, chemical characteristics, and potentially different biological effects. Therefore, knowing only the botanical name may not provide the complete picture when selecting an essential oil for a specific purpose.

 

Ensuring Quality Control from Start to Finish

Since this time, I have consistently been updating my knowledge on essential oil quality to ensure I’m still using high-quality oils that are free from unwanted synthetics and additives.

This means that in addition to examining the final product, I also assess the oil production method by asking the manufacturers about the following:

What is their sourcing process and raw materials?- Is the oil sourced from seeds that are organic, grown on pristine soil, and what is the global location of plant material?

What are their cultivation practices?- What are they and are they sustainable?

How do they monitor distillation time, temperature, pressure, and specs for each oil?- An oil’s chemical makeup varies with distillation time, and this can alter biological properties. (R) Shortcuts can speed up distillation time but may lead to changes in the oil’s chemical composition and quality.

What are their verification tests?- More on this below.

Are they carefully bottled and labeled using state-of-the-art equipment?- This helps protect the oil from light, heat, air, and other factors that can contribute to degradation and oxidation.

 

Verification Testing for Essential Oil Quality and Sourcing

Due to the complexity of essential oils, it’s important to use more than one verification test to evaluate the identity, composition, quality, and authenticity of the final product.

Here are some vital examples of tests to verify and identify quality essential oils and their components:

• Gas chromatography (GC)- identifies constituents using a temperature-controlled capillary column which separates mixtures into individual components.
• Mass spectrometry (MS)- identifies the various chemical components based on the mass-to-charge ratio of ions. (14)
• Flash Point– identifies fluids based on the lowest temperature at which vapors of a fluid will ignite.
• Optical Rotation– measures the direction and degree to which a substance rotates plane-polarized light. It can help characterize an essential oil and may provide clues about its identity or authenticity, but it does not independently establish purity or whether an oil is natural or synthetic. (15)
• Refractive Index– a dimensionless number that describes how light propagates through that medium.
• Specific Gravity– the ratio of the density of a substance to the density of a reference substance.
• Fourier transform infrared spectroscopy–creates a molecular fingerprint of the sample via the molecular absorption and transmission.
• Contamination testing including:
  • Heavy metals analysis (which aren’t usually distilled)
  • Microbial contamination

No single verification test provides a complete assessment of essential-oil quality or authenticity. These methods are most useful when considered together with botanical identity, sourcing, production practices, and other quality-control information.

 

A Few Words on Certificates of Analysis- Gas Chromatography/Mass Spectrometry (GC/MS)

A certificate of analysis (CA) is a document that details a product’s specifications and quality testing results. In regards to an essential oil, CAs will often include Gas Chromatography/Mass Spectrometry (GC/MS) results of the various molecules present and deemed important for that specific oil.

Unfortunately, it’s becoming harder these days to get an essential oil’s CA from some companies due to propriety claims and popularity. If you are able to obtain them, you will notice that they can vary greatly from vendor to vendor and from product to product.

I have discovered that GC/MS of essential oils have several caveats to consider, including:

• Standards do note equal quality: Not all essential oil manufacturers deem the same constituents as important in their products. This means if a standardized constituent is present, it doesn’t ensure the source is pure. Furthermore, if the constituent is absent, it doesn’t mean the oil is not pure.
• Some essential oils are 100% sourced from a company’s own farms, trusted suppliers, or esteemed producers of them. These companies should disclose if testing was in-house and/or third party verified.
• Not all producers are honest regarding their results, sources, verification, or production. You have to do more digging than just viewing the website claims.
• Acceptable values for the composition of components that are found on GC/MS of essential oils usually contain a range to account for the natural variations noted above. This is helpful for several reasons:
  • Essential oils that reside in the plant are constantly changing their chemical composition. Temperature, time of year, and environmental shifts will affect the secondary metabolites produced and which compounds are more prominent. (1, 2, 3, 4, 5, 6) This helps the plant to adapt to its ever-changing internal and external conditions.
  • Variations, therefore, can be a clue that the company is accounting for natural variation rather than artificially adjusting the oil to achieve a predetermined chemical profile. This reflects how the constituents within essential oils can change according to the plants’ needs and growing conditions.

In summary, GC/MS CAs are not the guarantee of purity or quality some believe them to be, as they report on the constituents that are present, but not oil purity.

 

Safe Application Tips for Essential Oils

Now that we know how to find good quality oils, here’s some quick safety tips for how to use them.

• Essential oils can be applied topically, diluted with a carrier oil, and avoiding sensitive areas. Please see this chart and start with the lowest dilution ratio when applying oils to the skin. Dilution should be individualized based on the oil, intended application, area of the body, and the person using it. A 2% dilution is commonly used for topical applications, while higher dilution ratios, such as 5% or more, may be appropriate for certain acute applications under supervision.
• You can also directly inhale essential oils from the bottle and diffuse them for their mind-body benefits.
• Some oils can be taken internally as needed. Internal use requires additional consideration because safety varies by oil, dose, formulation, route, duration, and individual factors. Please only use internal ingestion of essential oils under the care of a qualified expert who is knowledgeable about their appropriate use.

 

A Naturopathic and Functional Medicine Perspective

From a naturopathic and functional medicine perspective, essential oil selection goes beyond identifying a quality product or matching an oil to a symptom. Biochemical individuality recognizes that each person may respond differently based on their unique physiology, health history, genetics, environmental exposures, and other factors.

Essential oils also have multifaceted actions and may interact with multiple body systems simultaneously. Therefore, I am not comfortable with a one-size-fits-all approach to essential oil use. The goal is to consider the whole person and how an aromatic may fit within their individual health picture, rather than simply asking, “What oil is best for this symptom?”

This approach is consistent with personalized medicine and the naturopathic principle of treating the whole person.

 

Aromatic Personalization

There is another layer to individualized essential oil selection: the aroma itself.

Our response to a scent is influenced not only by the chemistry of an essential oil, but also by personal experience, memories, preferences, and associations. This psychological response can interact with the biological activity of the oil. An aromatic that is calming to one person may be unpleasant or even distracting to another.

This is one reason I believe aromatic discernment is an important part of clinical aromatherapy. The question is not simply whether an essential oil is high quality or whether it contains a particular constituent. It is also whether that particular aromatic is appropriate for the individual and the intended purpose.

In other words, the same botanical name does not necessarily mean the same aromatic experience—and the same aromatic will not necessarily be experienced the same way by every person. This is where quality assessment, chemistry, sensory experience, and individualized care come together.

 

Summary on Verifying Quality and Purity of Essential Oils

We’ve covered a lot in our quest for quality essential oils. Here’s a summary of what we’ve learned:

• Choosing high-quality essential oils requires research and asking manufacturers the right questions.
• Evaluating purity and quality means considering sourcing, production practices, verification, and quality assurance testing.
• A CA using GC/MS does not, by itself, guarantee an essential oil’s purity or quality. Testing identifies and characterizes constituents, but does not provide a complete assessment of the oil.
• Once you obtain high-quality essential oils, use them safely, mindfully, and appropriately for the individual and intended application.

Quality is more than a label or a single test. It requires looking at the whole picture—from the plant and its cultivation to sourcing, production, testing, storage, and application.

By working together to achieve high standards, accessibility, sustainability, safety, and better education around essential oils, we can help move the field toward greater transparency, discernment, and responsible use.

I look forward to hearing your comments and feedback

 

Resources

• Not All Essential Oils Are Equal (The English Aromatherapist)
• The Quality of Essential Oils (The School of Aromatic Medicine)
• Guide to Verifying Essential Oil Quality (AromaWeb)
• In Defense of Essential Oils: Synergy, Nature’s Wisdom, & Misleading Studies (My peer-reviewed article on NDNR)
• Why Do Consumers Prefer One Brand Over Another? The Economics and Sociology of Brand Competitiveness (Journal of Retailing and Consumer Services, May 2023.)
• Exploring the Complexities and Caveats of Safe Internal Use of Essential Oils for Pain: Highlighting Intestinal Discomfort, Part 1. (My peer-reviewed article originally published on Townsend Letter. Quality and Essential Oils Science)
• GetOiling Site (My branded essential oils website)
• The Many Benefits of Lavender Oil (My video article with scientific references, an example of essential oils studies)
• Essential Oils DIY Recipe Group
• A Personalized Diet Using a Naturopathic Medicine Approach to Nourishing the Body with Food (My article with references, biochemical individuality)
• Aromatherapy and Essential Oils: Holistic Strategies in Complementary and Alternative Medicine for Integral Wellbeing. (Plants (Basel). 2025 Jan 29;14(3):400.)