Fixed Oils vs Essential Oils: The Difference

The short version: essential oils are volatile, aromatic plant extracts, usually used a few drops at a time and diluted on skin. Fixed oils are fatty oils, usually pressed from seeds or nuts, that do not evaporate. One is not better than the other. They are different substances that do different jobs.

The two are easy to confuse because shops often sell them side by side, sometimes under the same label. We sell both kinds, so read this knowing that. The sources we used are listed at the end.

The difference at a glance

	Essential oil	Fixed oil
What it is	Volatile aromatic liquid	Fatty oil, made of glyceryl esters of fatty acids
How it is made	Steam distillation, pressing citrus peel, or dry distillation	Usually pressed from seeds, nuts or fruit
In open air	Evaporates	Stays; does not evaporate at room temperature
On paper	No permanent grease spot	Permanent grease spot
How it ages	Oxidises and can turn resinous	Goes rancid
Typical skin use	Diluted, a few drops at a time	Often the base that other things are mixed into

Compiled from the ISO, National Cancer Institute and pharmacognosy sources listed below.

What counts as an essential oil?

An essential oil is a volatile plant extract made by one of a few specific methods. The international vocabulary standard, ISO 9235, describes a product from a plant raw material obtained by steam distillation, by mechanical processes from citrus peel, or by dry distillation. The US National Cancer Institute likewise calls essential oils volatile liquids from aromatic plant material, and says oils made with chemical solvents are not considered true essential oils.

Despite the name, an essential oil is not a fat. Pharmacognosy teaching notes say volatile oils do not consist of glyceryl esters of fatty acids, the fats that make up ordinary plant oils.

What is a fixed oil?

A fixed oil is a fatty oil, and "fixed" means it does not evaporate away. Fixed oils are built from glyceryl esters of fatty acids. That is why they leave a lasting grease mark on paper, can be turned into soap with alkali, and go rancid with age.

Pharmacy texts also call them fatty oils or carrier oils. "Carrier" describes a job, diluting essential oils, while "fixed" describes what the oil is. Coconut, sesame, neem and flaxseed oil are all examples.

Why "cold-pressed" does not settle it

Cold-pressed describes a method, not a type of oil. Press the peel of a lemon and ISO 9235 calls the result a cold-pressed essential oil. Press a neem seed and you get a fatty oil. What you are pressing makes the difference, so look for the plant part on the label as well as the method.

Here is how our own range sorts out, as a worked example:

Oil	Method	Type
Lavender, Rosemary, Peppermint, Eucalyptus, Tea Tree	Steam-distilled	Essential oil
Lemon, Orange	Cold-pressed peel	Essential oil
Neem, Black Seed, Flaxseed, Poppy Seed	Cold-pressed	Fixed oil
Golden Jojoba	Cold-pressed	Liquid wax, usually grouped with fixed oils

Two oils that break the simple rule

Jojoba is a liquid wax

Jojoba is sold and used like a fixed oil, but it is chemically different. A 2021 review puts wax at about 98% of the oil, mainly wax esters, with few triglycerides, and notes that it is widely known as a liquid wax rather than an oil or fat. The same review describes its oxidative stability as high. More in our piece on why jojoba is not really an oil.

Black seed can give two different oils

Black seed (Nigella sativa) contains both kinds. One review lists fatty oil at 35.6–41.6% of the seed and volatile oil at just 0.5–1.6%. So pressed black seed oil is a fixed oil, and it is not interchangeable with an essential oil distilled from the same seed. Always check how it was made.

Why the difference matters in practice

Dilution

The National Cancer Institute notes that aromatherapy massage uses essential oils diluted in a carrier oil. Fixed oils are commonly the base for that mix. If you take a pressed seed oil for an essential oil, you may use it by the drop when it was meant to be the base. Make the opposite mistake and you could put far too much of a concentrated extract on your skin. Our carrier oil guide covers ratios.

Sun

Phototoxic reactions have occurred when essential oils, particularly citrus oils, were applied to skin before sun exposure, according to the National Cancer Institute. The Tisserand Institute says lemon oil should be used at no more than 2% to avoid that risk.

Storage

Fixed oils go rancid, and essential oils oxidise and can turn resinous when exposed to light and air, so keep both tightly closed and away from light and heat. Oils rich in polyunsaturated fats need the most care. Flaxseed oil is 39–60% alpha-linolenic acid and, according to one review, oxidises easily. Linoleic acid made up about 71–74% of the poppy seed oils tested in one study.

Buying

A clear label should tell you the plant, the part used and the method. If a pressed seed oil is sold as an essential oil, the label is using the wrong word, whatever the quality of the oil inside. Compare it with other fixed oils, not with distilled ones.

Try the paper test, and know its limit

Put one drop of oil on plain paper and check it the next day. Fixed oils leave a permanent grease spot, and volatile oils do not. It is a rough clue to the kind of oil you have.

It does not prove purity. An essential oil mixed with a fatty oil would still leave a spot, and some essential oils can leave a coloured mark. Only lab analysis can establish what is in the bottle.

Frequently asked questions

Is neem oil an essential oil?

No. Neem oil is pressed from the seed and is a fatty oil made up mainly of fatty acids such as oleic and linoleic acid. It is a fixed oil, even when a label calls it an essential oil.

Does cold-pressed mean an oil is a fixed oil?

Not always. Pressing citrus peel gives an essential oil, as the ISO definition recognises. Pressing seeds or nuts gives a fixed oil. The part of the plant tells you more than the word cold-pressed does.

Are carrier oils and fixed oils the same thing?

Largely, yes. Carrier is a job and fixed is a type: most carrier oils are fixed oils used to dilute essential oils. Jojoba is the common exception, because it is chemically a liquid wax.

Is black seed oil an essential oil?

Pressed black seed oil is a fixed oil. The seed holds far more fatty oil than volatile oil: one review lists 35.6–41.6% fatty oil against 0.5–1.6% volatile oil. A true black seed essential oil would be a different product.

Can I test at home which kind of oil I have?

A drop on paper gives a rough clue. Fixed oils leave a permanent grease spot, while volatile oils do not. It cannot prove purity, because an essential oil mixed with a fatty oil would leave a spot as well.

Fixed Oils vs Essential Oils: What's the Difference?