The Aromatherapy Glossary: Key Terms Every Enthusiast Should Know

Whether you're just starting out or deepening an existing practice, aromatherapy comes with its own vocabulary. Understanding these terms helps you make better choices, read labels with confidence, and get more from your oils and incense. Here's a plain-English guide to the most important ones.

A

Absolute
A highly concentrated aromatic extract obtained through solvent extraction rather than steam distillation. Absolutes are typically used for delicate flowers (like rose or jasmine) whose aromatic compounds are too fragile for steam. They are more complex and often more expensive than essential oils.

Adulteration
The practice of diluting or blending an essential oil with cheaper substances — synthetic fragrances, carrier oils, or lower-quality oils — without disclosure. Adulteration is widespread in the industry and is one of the key reasons sourcing from reputable suppliers matters. See our guide to How to Choose Quality Essential Oils.

Aromatherapy
The therapeutic use of aromatic plant extracts — primarily essential oils and incense — to support physical, emotional, and psychological wellbeing. The term was coined by French chemist René-Maurice Gattefossé in 1937.

B

Base Note
In perfumery and blending, base notes are the heaviest, slowest-evaporating aromatic compounds. They form the foundation of a blend and linger longest. Common base notes include vetiver, cedarwood, sandalwood, patchouli, and frankincense.

Botanical Name
The Latin scientific name of a plant, used to distinguish between species that share a common name. For example, "lavender" can refer to Lavandula angustifolia (true lavender), Lavandula latifolia (spike lavender), or Lavandula x intermedia (lavandin) — each with different properties. Always check the botanical name when buying essential oils.

C

Carrier Oil
A vegetable oil used to dilute essential oils before applying them to skin. Carrier oils "carry" the essential oil safely onto the skin without causing irritation. Common carrier oils include sweet almond, jojoba, fractionated coconut, and rosehip. See our Essential Oil Dilution Guide for dilution ratios.

Chemotype (CT)
A chemotype is a plant of the same species that produces a different chemical composition due to growing conditions, geography, or genetics. Rosemary, for example, comes in several chemotypes — ct. camphor, ct. cineole, and ct. verbenone — each with distinct therapeutic properties. Chemotype is usually indicated on quality oil labels.

Cold Pressing
An extraction method used primarily for citrus oils (lemon, orange, grapefruit, bergamot). The rind is mechanically pressed to release the aromatic compounds without heat. Cold-pressed oils retain a fresher, brighter scent than steam-distilled equivalents but have a shorter shelf life.

CO₂ Extraction
A modern extraction method using pressurised carbon dioxide to extract aromatic compounds. CO₂ extracts are often considered superior to steam-distilled oils as they more closely resemble the natural plant aroma and retain a broader range of compounds. They are typically more expensive.

D

Diffuser
A device that disperses essential oil molecules into the air. The most common types are ultrasonic diffusers (which use water and vibration) and nebulising diffusers (which use pressurised air and no water, producing a more concentrated output). See our guide to diffusing for more detail.

Dilution
The process of mixing essential oils with a carrier oil to a safe concentration for skin application. Standard dilution rates are 1–2% for adults (1–2 drops per teaspoon of carrier oil), lower for children, the elderly, and sensitive skin. Never apply undiluted essential oils to skin.

E

Essential Oil
A concentrated, volatile aromatic compound extracted from plant material — flowers, leaves, bark, roots, resin, or peel. Essential oils are not actually "oily" in the traditional sense; they are volatile liquids that evaporate quickly at room temperature. They are produced primarily by steam distillation or cold pressing.

F

Fixed Oil
Another term for carrier oil — a non-volatile vegetable oil that does not evaporate. Fixed oils are used to dilute essential oils and as a base for massage blends and skincare preparations.

Frankincense
One of the most historically significant aromatic resins, derived from Boswellia trees. Used for millennia in religious ritual, medicine, and skincare. Available as resin (for burning), essential oil, and CO₂ extract. See The History of Frankincense for more.

G

GC/MS Testing
Gas Chromatography/Mass Spectrometry — the gold standard analytical test for essential oil quality and purity. GC/MS testing identifies and quantifies the chemical constituents of an oil, confirming authenticity and detecting adulteration. Reputable suppliers make GC/MS reports available to customers.

M

Middle Note
In blending, middle notes form the heart of a fragrance. They emerge after the top notes fade and last longer. Common middle notes include lavender, geranium, rosemary, chamomile, and ylang ylang.

N

Neat Application
Applying an undiluted essential oil directly to skin. This is generally not recommended — most essential oils can cause irritation, sensitisation, or burns when applied neat. Lavender and tea tree are sometimes cited as exceptions, but even these should be diluted for regular use.

O

Oleoresin
A natural mixture of essential oil and resin found in certain plants (pine, frankincense, myrrh). Oleoresins can be used directly as incense or processed to separate the essential oil and resin components.

P

Phototoxicity
A reaction that can occur when certain essential oils — particularly cold-pressed citrus oils (bergamot, lemon, lime, grapefruit) — are applied to skin that is then exposed to UV light. This can cause burns, blistering, or permanent pigmentation changes. Always check whether an oil is phototoxic before applying before sun exposure. Our safety guides cover this in detail.

R

Resin
A solid or semi-solid aromatic substance produced by certain trees and plants (frankincense, myrrh, benzoin, copal). Resins have been burned as incense for thousands of years and are also used to produce essential oils and absolutes.

S

Sensitisation
An immune response that can develop from repeated exposure to an essential oil, particularly when used neat or at high concentrations. Once sensitised, a person may react to even tiny amounts of the oil. Sensitisation is permanent and is one of the key reasons proper dilution matters.

Steam Distillation
The most common method of essential oil extraction. Steam is passed through plant material, causing the aromatic compounds to vaporise. The vapour is then cooled and condensed, separating into essential oil and hydrosol (floral water).

Synergy
In blending, synergy refers to the phenomenon where a combination of essential oils produces a greater therapeutic effect than any single oil alone. A well-constructed blend is said to be synergistic.

T

Therapeutic Grade
A marketing term with no standardised industry definition or regulatory backing. There is no official grading system for essential oils — "therapeutic grade" is not a certification. Quality is better assessed through GC/MS testing, botanical sourcing, and supplier transparency.

Top Note
The first aromatic impression of an oil or blend — volatile compounds that evaporate quickly. Top notes are bright and immediate but fade fastest. Common top notes include citrus oils, peppermint, eucalyptus, and basil.

V

Volatile
A substance that evaporates readily at room temperature. Essential oils are volatile — this is what allows them to be diffused and inhaled. Carrier oils are non-volatile (fixed oils).

Further Reading

Dive deeper into any of these topics through our sub-guides:

• Essential Oil Guides — choosing, using, and understanding oils
• Incense Guides — types, history, and how to burn
• Aromatherapy Practices — routines, diffusing, and meditation
• Safety & Care — dilution, safety, and storage