Bookmark this page. Every specialist term we use anywhere on the site is defined here in plain English.
A
Absolute — A highly concentrated aromatic extract produced with solvents (usually hexane), rather than steam distillation. Common for delicate flowers like rose, jasmine, and tuberose where steam would destroy the scent. Technically not an "essential oil" in the purist sense.
Adulteration — Watering down or faking an essential oil by adding cheaper oils, synthetic fragrance molecules, or solvents. A chronic problem in the industry — which is why GC/MS testing matters.
Anosmia — The inability to smell, either temporarily (after a cold or COVID) or permanently.
Aromatherapy — The practice of using the aromatic compounds in plant oils for psychological or physical wellbeing. Includes inhalation, dermal application (diluted), and environmental diffusion.
AromaWeb / NAHA / Tisserand — Reputable English-language aromatherapy references. NAHA is the US professional association; Tisserand & Young's Essential Oil Safety is the standard clinical reference.
B
Base note — In perfumery, the scent that lingers longest after application — typically woody, resinous, or earthy. Examples: sandalwood, vetiver, frankincense. Low volatility.
Batch number / GC/MS lot — The production batch of an oil. A trustworthy brand prints or publishes a GC/MS report keyed to the batch you bought.
Blend — Two or more essential oils mixed together, ideally with a balance of top, middle, and base notes.
C
Carrier oil — A non-volatile, fatty plant oil used to dilute essential oils before skin contact. Examples: jojoba, coconut (fractionated), sweet almond, argan, grapeseed.
Chemotype (CT) — A plant that produces different chemical profiles depending on where it's grown. Rosemary, for example, has three major chemotypes: 1,8-cineole, camphor, and verbenone. Matters because the safety profile changes with the chemotype.
Clinical aromatherapy — Aromatherapy practiced in a medical, hospice, or therapeutic setting by a trained practitioner. Different from at-home use.
Cold-pressed / expression — The extraction method used for citrus peel oils (lemon, orange, bergamot). No heat, no solvent.
D
Dermal limit — The maximum recommended percentage of an oil for safe skin application, as published by IFRA or Tisserand & Young. Bergamot, for example, has a dermal limit of 0.4% when not FCF (see FCF).
Dilution — Mixing an essential oil into a carrier before skin use. Expressed as a percentage of essential oil in the total blend (e.g. 2% dilution = 12 drops of EO in 30 mL of carrier).
Diffusion — Dispersing essential oils into the air. Ultrasonic diffusers use water and a vibrating disc; nebulizing diffusers use pressure alone; heat diffusers warm the oil (not recommended — degrades the oil).
Distillation — The dominant extraction method for most essential oils. Plant material is steamed; the volatile aromatic compounds rise with the steam, condense in a cooled tube, and separate from the water.
E
Essential oil (EO) — A concentrated aromatic oil extracted from a plant, containing the plant's volatile aromatic compounds. Typically produced by steam distillation or (for citrus) cold expression.
Expression — See cold-pressed.
F
FCF (Furocoumarin-Free) — A citrus oil (usually bergamot) processed to remove bergapten, the compound that causes severe phototoxic burns on skin exposed to UV light. Safer for topical use.
Fixed oil — Another term for carrier oil. "Fixed" because it doesn't evaporate.
Fractionated coconut oil (FCO) — Coconut oil with the long-chain fatty acids removed, leaving a liquid, odorless, long-shelf-life carrier. The most common carrier for roller bottles.
Functional group — In chemistry, the family a compound belongs to — alcohols, esters, phenols, aldehydes, etc. Tisserand-era safety guidance often organizes oils by functional-group profile.
G
GC/MS (Gas Chromatography / Mass Spectrometry) — The gold-standard lab test that breaks an oil into its component compounds and measures the ratio of each. Reputable brands publish the GC/MS report for every batch. Without a GC/MS, "therapeutic grade" means nothing.
Grade — A marketing word. There is no industry-standard "grade" for essential oils; terms like "therapeutic grade" are unregulated and essentially meaningless. Look at GC/MS data instead.
H
Hydrosol (hydrolat / floral water) — The aromatic water byproduct of steam distillation. Much milder than the essential oil itself. Rose hydrosol, lavender hydrosol, and neroli hydrosol are common for skincare.
I
IFRA (International Fragrance Association) — The global body that publishes fragrance safety standards, including maximum dermal concentrations for individual compounds.
Inhalation — Using an oil by breathing its aromatic molecules, either passively (diffusion) or directly (from a bottle, personal inhaler, or steam bowl). Generally considered the safest use method.
L
Latin name (botanical name) — The genus + species of the plant (e.g. Lavandula angustifolia). Matters because common names are wildly imprecise — "eucalyptus" could mean any of 60+ species with different safety profiles.
M
Middle note — In perfumery, the heart of a blend — appears after the top notes fade, lasts longer. Examples: lavender, geranium, clary sage, rosemary.
MLM (Multi-Level Marketing) — A business model where salespeople earn commission on their own sales plus a cut of the sales of those they recruit. doTERRA and Young Living are the two major MLM essential-oil brands. Our stance.
N
NAHA (National Association for Holistic Aromatherapy) — The US-based professional body for aromatherapists. Publishes safety guidance and maintains a register of certified practitioners.
Neat — Using an essential oil undiluted, directly on skin. Not recommended for almost any oil in almost any context. Exceptions are vanishingly rare and should only be done under clinical guidance.
O
Organic — USDA Organic or equivalent certification (EU, Soil Association UK, etc.). Means the plants were grown without synthetic pesticides or fertilizers. Doesn't guarantee purity in the distillation — but is a good baseline.
P
Patch test — Before using a new oil on skin: apply a dilute drop to the inside of your forearm, wait 24 hours, check for redness, itching, or bumps. Always worth doing.
Phenol — A class of aromatic compounds that includes thymol, carvacrol, and eugenol (oregano, thyme, clove). Very potent — skin irritants at high concentration, often hepatotoxic in excess. Respect them.
Photosensitivity / phototoxicity — A reaction where certain oils (most citrus, especially expressed bergamot and cold-pressed lime) cause severe burns when the treated skin is exposed to UV light for 12+ hours after application. Avoid sun after use, or use FCF versions.
Pure — A marketing word. "100% pure" is meaningless without a GC/MS report. A heavily adulterated oil can still be labeled "pure".
R
Roller / roll-on — A small bottle with a rollerball top, usually 10 mL, filled with carrier oil + a dilute essential-oil blend for on-the-go application to wrists, temples, or neck.
S
Sensitization — An allergic-like reaction that builds up over repeated exposure. You can develop sensitization to an oil you've used safely for years. Cinnamon bark, lemongrass, and oxidized lavender are common culprits.
Sustainability — Many essential oils are produced from plants under ecological stress (sandalwood, rosewood, frankincense). Responsible brands source from sustainable plantations or certified wild-harvest programs.
Synergy — When a combination of oils produces an effect greater than the individual oils alone. Empirically common in perfumery, less firmly established clinically.
T
Therapeutic grade — Not a thing. A marketing term with no regulatory meaning. Ignore it; look for GC/MS reports instead.
Tisserand (Robert) — The aromatherapy author and safety researcher whose book Essential Oil Safety (2nd ed., with Rodney Young) is the standard clinical reference.
Top note — The first scent you smell in a blend — citrus, eucalyptus, peppermint. Highly volatile, evaporates fastest.
U
Ultrasonic diffuser — The most common household diffuser. Uses water and a vibrating ceramic disc to create a fine mist of water + oil. Quiet, safe around kids and pets, 3–8 hour run time. Recommended for beginners.
V
Volatile — Able to evaporate readily at room temperature. Essential oils are, by definition, volatile. Carrier oils are not.
W
Wildcrafted — Harvested from wild plants rather than cultivated. Can be ecologically harmful (sandalwood, rosewood) or benign (local lavender). Read the brand's sourcing statement.