Aromatherapy Vocabulary in English — 20 Essential Terms

An essential oil is a highly concentrated aromatic extract from a plant, capturing its active compounds and characteristic scent. It is too potent to apply directly to skin in most cases. A carrier oil is a plain, fatty plant oil — such as sweet almond, jojoba, or coconut oil — used to dilute the essential oil to a safe concentration before skin application. Carrier oils do not have a strong scent and do not evaporate quickly, which distinguishes them clearly from volatile essential oils.

Steam distillation works by passing pressurised steam through plant material — leaves, flowers, bark, or roots — causing the aromatic compounds to vaporise. The vapour is then passed through a cooling chamber where it condenses back into liquid. Because oil and water do not mix, the essential oil floats to the top and is separated. The remaining water, known as a hydrosol, is also kept for use. This is the most widely used method for extracting essential oils from most plant types.

In chemistry, volatile describes a substance that evaporates easily at room temperature. Essential oils are volatile because their molecules are small and light enough to enter the air rapidly, which is why you can smell them so quickly when you open a bottle. This volatility is also why essential oils must be stored in sealed dark glass containers — exposure to air, light, and heat causes them to evaporate and degrade, reducing both their scent and their therapeutic value.

A synergy blend is a combination of two or more essential oils chosen because they work together in a way that produces a greater or qualitatively different effect than any single oil used alone. For example, lavender and frankincense are often blended because their combined calming and grounding qualities are considered more effective for promoting relaxation than either oil individually. Aromatherapists develop synergies by understanding the chemical profiles of oils and how their constituents interact.

Essential oils are extremely concentrated and can cause skin irritation, chemical burns, or allergic reactions when applied undiluted. Dilution in a carrier oil reduces the concentration to a safe level — typically one to three per cent for adults — while still allowing the active compounds to be absorbed through the skin. Dilution also helps the oil spread more easily over a larger area and slows its evaporation, prolonging the aromatic effect. Some oils, such as cinnamon bark and clove, are particularly likely to cause irritation and require careful dilution.

Phototoxic essential oils contain compounds — most commonly furanocoumarins — that react with ultraviolet light from the sun or tanning beds and can cause accelerated sunburn, blistering, or long-lasting dark patches on the skin. The main phototoxic oils are cold-pressed citrus oils: bergamot, lime, lemon, grapefruit, and bitter orange. If you apply these oils to skin that will then be exposed to sunlight, you risk a phototoxic reaction. Either avoid sun exposure for 12–24 hours after application, or use steam-distilled or “bergapten-free” versions of these oils, which have had the problematic compounds removed.

These terms come from perfumery and are used in aromatherapy blending to describe how quickly an oil's scent evaporates and when it is perceived. Top notes are light and volatile — the first scent you notice, which fades within minutes; citrus oils are classic examples. Middle notes, also called heart notes, form the main character of a blend and last for an hour or two; lavender and geranium are typical middle notes. Base notes are heavy, slow to evaporate, and provide lasting depth; sandalwood, vetiver, and patchouli are well-known base notes. Skilled blending involves balancing all three layers.

A contraindication is a medical or personal condition that makes it inadvisable or unsafe to use a particular essential oil or treatment. For example, several oils — including clary sage, rosemary, and wintergreen — are contraindicated during pregnancy because they may stimulate contractions or affect the foetus. Certain oils should also be avoided by people with epilepsy, high blood pressure, or sensitivity to particular plant compounds. A qualified aromatherapist always takes a full health history from a client before designing a treatment in order to identify any relevant contraindications.

A hydrosol is the water-based liquid produced alongside an essential oil during steam distillation. It contains small amounts of water-soluble plant compounds and trace quantities of essential oil, giving it a mild version of the plant's aroma and some of its properties. Unlike an essential oil, a hydrosol is already water-based, so it does not need to be diluted before applying to skin and is considered gentler — suitable for children, sensitive skin, or use as a facial toner. Rosewater and lavender water are the most familiar hydrosols.

The most effective approach is to connect the words to sensory experience. When you smell a lavender essential oil or use a diffuser, mentally label what you are doing using the vocabulary on this page — inhalation, volatile, top note. Reading product labels and ingredient lists in English is another excellent way to encounter these words in authentic contexts. Practise the 20 terms with Flash Cards on LexFizz, then test yourself with the Matching Pairs exercise. Returning to the words in different contexts will help you retain them much more effectively than rote memorisation.