In Vietnam the Vietnamese word for essential oil is used for a great many things: a bottle of oil distilled from cajeput leaves, a ready-mixed scent for a diffuser, a gel tin hanging in a car, even rose water. Most of them are not essential oils in the sense the standards use. This article sets out what an essential oil is by the formal definition, the things most often mistaken for one, and how to read a label to know what you are holding.
The definition in the standard
Vietnam has its own vocabulary standard for this field, TCVN 11582:2016, built on ISO 9235:2013. Under it, an essential oil is a product obtained from a natural raw material of plant origin by one of three routes:
- steam distillation;
- mechanical expression of the peel of citrus fruit;
- dry distillation (without water, as with some woods and resins).
Any water phase is then separated by physical means. The oil may be filtered, decanted or centrifuged, because those steps do not change its composition significantly.
This is far narrower than everyday usage. It says nothing about scent, price, or how "natural" a product is. It asks one thing only: how the oil was obtained. Anything taken out with a solvent, with alcohol or with fat is not an essential oil, even when it comes from the same flower.
What is in a bottle of essential oil
An essential oil is not one substance. It is a mixture of tens to hundreds of components, most of them terpenes and their derivatives: alcohols, aldehydes, esters, oxides, phenols. What they share is that they are light enough to travel with steam, and so light enough to reach the nose.
Two consequences are worth knowing:
- An essential oil is not a fatty oil. It is called an oil because it does not dissolve in water, but chemically it is nothing like cooking oil. Put a drop of a light oil such as lemongrass or orange on paper and leave it a few hours, and the paper is nearly dry again. Cooking oil leaves a spot that stays.
- The composition varies. The same species, grown in another region, harvested in another season or distilled from another part of the plant, gives a different oil. The articles on chemotypes and growing regions explain why. That is why each oil has its own standard, such as TCVN 11425 for lemongrass or TCVN 11883 for lavender, and why a standard gives a range rather than a single number.
Things often called essential oil
| Product | How it is obtained | Is it an essential oil |
|---|---|---|
| Distilled or expressed oil | steam, expression of citrus peel, dry distillation | Yes |
| Absolute | solvent extraction, then an alcohol wash | No. Closer to the flower, but a different product |
| CO₂ extract | supercritical CO₂ | No. The standard classes it as an extract |
| Oleoresin | solvent extraction of a spice | No. It also carries the pungency, as with ginger |
| Hydrosol | the water left after distillation | No. It is the part separated from the oil |
| Infused oil (garlic oil, fried lemongrass oil) | plant material steeped in cooking oil | No. It is a cooking oil that smells |
| Fragrance oil | blended from synthetics, with or without essential oil | No |
The last row is the commonest on the market. Most cheap bottles sold as "essential oil" for diffusers, candles or cars are fragrance oils. A fragrance oil is not a bad thing. It is cheap, its scent is consistent, and it can do scents no plant yields as an oil, such as apple, sea breeze or "fresh laundry". The only problem is the name: if the label calls it essential oil, the buyer cannot tell what they are paying for.
The page on label words sets each type side by side, with its texture, composition and where people go wrong.
What "natural essential oil" means
By the definition above, an essential oil already comes from a plant. Adding the word "natural" says nothing more about quality. No body grants a "natural" grade to essential oils, just as no one issues a purity certificate.
The word is useful in one place: it separates essential oil from fragrance oil. But whether it is true cannot be read from the label. A synthetic linalool and a plant linalool have the same formula. They differ only in things an instrument has to find, such as the ratio of the two mirror-image forms or the carbon isotope ratio.
Reading the label: five lines it should have
A complete essential oil label answers five questions:
- The botanical name. "Eucalyptus oil" can be three or four different species. The Latin name points to one. The article on species names explains why even that is not quite enough.
- The plant part. Leaf, peel, flower, root or wood give different oils, even from the same plant. The article on plant parts has examples.
- The method. Distilled, expressed, or extracted. This line tells you whether it is an essential oil at all.
- Where it was grown.
- The lot number, and a GC/MS analysis of that exact lot.
If a line is missing, ask the seller for it. Six things sellers often say suggests how to ask.
Sources
- TCVN 11582:2016 (ISO 9235:2013). Aromatic natural raw materials. Vocabulary.
- ISO 9235:2021. Aromatic natural raw materials. Vocabulary.
- TCVN 11425:2016. Oil of lemongrass. TCVN 11883:2017. Oil of lavender.