Aromatherapy is More Than Scent

Plants communicate through chemistry. The aroma of a leaf, flower, peel, seed, resin or wood comes from volatile compounds the plant produces for its own purposes. They can attract pollinators, discourage predators, protect the plant, or communicate with the environment around it. Aromatherapy begins with these chemical compounds.

When I work with an essential oil, I want to know the plant behind it. What species is it? What part of the plant was used? Where was it grown? Was the aromatic material steam distilled, expressed, extracted with CO₂, or produced another way? What are its dominant constituents? How volatile is it? How does it behave by itself, and what happens when I put it beside another oil?

But I also smell it. Because the chemistry can tell me a great deal, but it cannot replace the experience of the aroma itself. Eucalyptus feels expansive and penetrating. Fennel is sweet and warm and has movement. Lavender changes depending on what surrounds it. Vanilla can completely alter the shape of a blend without dominating it.

Botany leads into chemistry. Chemistry leads into the senses. The senses lead into memory and emotion. Then you add oil, skin, touch and the individual person, and the experience changes again.

An essential oil is not the same thing as the plant

An essential oil is one particular expression of a plant. It contains many of the plant's volatile, aromatic compounds, but it does not contain everything that was present in the original plant material. When lavender is steam distilled, for example, steam carries volatile molecules out of the plant material. As that vapor cools, the aromatic oil separates from the water. The resulting essential oil contains compounds that were volatile enough to travel through that process. It does not contain the plant in its entirety.

The same distinction applies to many herbs used both in Ayurveda and aromatherapy. A tea made from fennel seed, fennel essential oil and whole fennel used in food are related, but they are not interchangeable preparations. Their chemistry is different. Their concentration is different. Their route into the body is different. This matters because traditional herbal knowledge can sometimes get transferred too casually to essential oils. If an herb has historically been used for a particular purpose, it does not automatically follow that its essential oil should be used in the same quantity, by the same route or with the same expectations. Aromatherapy requires its own knowledge.

What is actually inside an essential oil?

Essential oils are chemically complex. A single oil can contain dozens or even hundreds of constituents in different proportions. Among the major families encountered in essential-oil chemistry are monoterpenes, sesquiterpenes, alcohols, esters, aldehydes, ketones, oxides and phenols. You don't need to become an organic chemist to use essential oils intelligently, but understanding these families changes the way you think about an oil.

Eucalyptus is a good example. Many eucalyptus oils are rich in 1,8-cineole, also called eucalyptol, an oxide responsible for much of the penetrating aroma we immediately associate with eucalyptus. But saying “eucalyptus” still isn't specific enough. There are hundreds of species in the genus Eucalyptus, and their oils do not all have identical chemical profiles.

Lavender gives us another example. True lavender, Lavandula angustifolia, is generally characterized by significant amounts of linalool and linalyl acetate, although the percentages vary. Those constituents contribute to the aromatic character and biological activity associated with the oil.

Then consider rose geranium. Depending on species, origin and composition, we encounter constituents such as citronellol and geraniol, giving it a very different chemical and aromatic profile.

Each plant has a botanical identity, and its oil has a chemistry.

Chemotype: when the same plant isn't chemically the same

One of the concepts that begins to separate serious aromatherapy from casual essential-oil use is chemotype. Plants of the same botanical species can sometimes produce oils with significantly different dominant chemical constituents depending on genetics and growing conditions. Thyme is a classic example. Thymus vulgaris can produce different chemotypes, including oils dominated by thymol, linalool or other constituents.

Those oils come from the same species but they are not functionally identical: their aroma differs, their safety considerations can differ, and the way an aromatherapist chooses to use them can differ.

Extraction changes what we receive

Steam distillation is probably the process people associate most with essential oils, but it is not the only method used to obtain aromatic materials. Many citrus oils are expressed from the peel rather than distilled. This distinction matters because expressed citrus oils can retain compounds that affect their safety profile, including constituents associated with phototoxicity in certain oils.

Some delicate flowers do not tolerate steam distillation well. Aromatic materials may instead be obtained through solvent extraction, producing an absolute rather than a conventional essential oil.

CO₂ extraction uses carbon dioxide under pressure and can produce still another aromatic profile.

Then there are hydrosols—the aromatic waters produced during distillation—which have their own chemistry and uses.

These are different manufacturing techniques for producing the same substance, but the extraction method influences what ends up in the finished material.

Aromatherapy works through more than one pathway

When an essential oil is inhaled, volatile molecules reach the olfactory epithelium high in the nasal cavity and interact with olfactory receptors. That signal is processed through the olfactory system, which has unusually direct relationships with brain regions involved in memory, emotion and behavioral response. This helps explain something people have understood experientially for a very long time: smell can alter the feeling of a moment almost immediately. A scent can bring back a childhood kitchen, a person, a hospital room, a forest or a particular period of life before you have consciously identified the memory.

The physical molecules themselves also matter greatly. When volatile aromatic compounds are inhaled, some can enter systemic circulation through the respiratory tract. When appropriately diluted essential oils are applied to the skin, certain constituents can penetrate the skin to varying degrees.

So there are several things happening at once: perception, memory and association, and physical alchemy. In the context of experience, take bodywork for example, there is also touch, temperature, pressure and movement.

Trying to reduce all of this to “lavender makes you calm” misses much of what makes aromatherapy interesting.

The architecture of a blend

Essential oils are concentrated materials; more is not automatically better. In fact, one of the marks of good aromatic formulation is knowing how little may be required to create the desired effect. There is a point at which increasing concentration does not improve the experience. It may make the aroma less nuanced, increase the possibility of skin irritation or sensitization, and overwhelm the olfactory system.

The appropriate dilution depends on the oil, the area of the body, the intended use, the frequency of application and the person using it. A small amount used occasionally on a healthy adult is a different situation from a product applied over the entire body every day.

When I formulate a blend, I am thinking about chemistry, but I am also listening to the aroma itself. Perfumery gives us the useful language of top, middle and base notes. Top notes are generally more volatile. They arrive quickly and often create the first impression of a blend. Middle notes develop through the center. Base notes evaporate more slowly and give depth, persistence and structure.

Essential-oil blending does not follow these categories as rigidly as a textbook diagram might suggest, but the concept is useful because a blend unfolds over time. What you smell when you first open a bottle is not necessarily what remains on the skin twenty minutes later.

The carrier oil is also part of the formula. Sesame oil and coconut oil are different materials with different fatty-acid profiles, textures, absorption characteristics and traditional uses.

From an Ayurvedic perspective, they also carry different qualities. Sesame is traditionally warming and is used extensively in Ayurvedic oil therapies. Coconut is associated with a more cooling quality. So when I formulate an aromatic body oil, I think about the experience of the oil and who it is for.

Training the nose

Sometimes you need to just put the information away and smell. What arrives first? What happens after thirty seconds? What remains after five minutes? Smell it from a blotter and then appropriately diluted in a carrier. Is it different on skin? Come back another day. Compare it with another species or another oil from the same botanical family.

Eventually the plant becomes recognizable to you- it's brightness, weight, penetration, power. In time, and with the right attention, the relationship to the plant and its chemical potency becomes intimate, and your ability to sense its power within you heightens your ability to connect.