How Essential Oils Are Made: Steam Distillation, Cold Pressing and Solvents
How essential oils are made on an industrial scale, as published sources describe: steam distillation, cold pressing of citrus peel and solvent extraction, and what each method changes.
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Essential oils are made by taking the smell-carrying chemicals out of a plant, and there is more than one way to do it. Which method is used depends mostly on the plant part. This page describes the industrial processes as published sources explain them. It does not give instructions for making oils at home, and we do not provide any.
A review of fragrance oils in cosmetics says that, once plants are harvested, oils are extracted by steam distillation, expression (physical crushing of the oil glands in fruit rinds), microwave-assisted extraction, solvent extraction or enfleurage. Steam distillation is the most common overall, and expression is most commonly used for citrus peel. [1] A US poison center says the same in plain terms: essential oils are often extracted by pressing or steam distillation. [2]
The main methods
| Method | What happens, according to the sources | Typical materials | What to know |
|---|---|---|---|
| Steam distillation | Steam passes through the plant material; the volatile compounds are carried off by the steam, cooled back into liquid and separated from the water layer by differences in density. [3] | Varies by plant | Widely used and does not need organic solvents. [3] Long heating and water exposure may alter delicate or very volatile compounds. [3] |
| Hydrodistillation | The plant material is placed in boiling water, rather than having steam pass through it. [3] | Varies by plant | The type of distillation changed yield and composition in studies of rosemary and lavender species. [3] |
| Expression ("cold pressing") | Physical crushing of the oil glands in the fruit peel. [1] | Citrus peel such as orange, lemon and bergamot | Pressed citrus oils carry heavier compounds, such as waxes and furocoumarins, that are unlikely to distill. [4] |
| Solvent extraction | An organic solvent pulls out aromatic material. The products are called concretes, absolutes, resinoids and oleoresins and can contain waxes, pigments and resins as well as scent compounds. [3] | Varies by plant | One 2026 review calls these "aromatic extracts" rather than classical essential oils. [3] Traces of solvent in the final product are a possibility the same review notes. [3] |
| Enfleurage | The scent is transferred from flower petals to fat. [1] | Flower petals | The sources we read do not say how widely it is used today. |
| Supercritical carbon dioxide | Carbon dioxide under pressure is used as the solvent, which a review says can reduce organic-solvent residues and heat damage. [3] | Varies | Needs specialized equipment. [3] |
Why citrus oils are different
Citrus oils are usually pressed, not distilled. Pressing keeps compounds that a still would leave behind, including furocoumarins. [4] Furocoumarins are phototoxins, meaning they can cause a skin reaction when the skin is then exposed to UVA light. A review says they are found mainly in expressed citrus peel oils, and that reactions can range from pigmentation and blistering to severe burns. [1] The FDA says certain citrus oils used safely in food can also be harmful in cosmetics, particularly on skin exposed to the sun. [5] We did not read a source that tests distilled citrus oils for sun reactions, so we do not say that a distilled citrus oil is free of this risk. The full topic is on Phototoxicity: citrus oils and sunlight.
What the method changes
- The mix of chemicals. Studies of rosemary, lavender and other species found that the type of distillation affected oil yield and chemical composition. [3] The plant, its growing conditions and its harvest also matter, which is one reason essential oils are hard to standardize. [1]
- What the label means. Two bottles of the same named oil can differ because of the method, the plant and the batch. A published analysis of neroli, mandarin and bergamot oils bought online found that more than 45 percent of the samples failed a composition check against ISO and AFNOR ranges. [4] The details are on Essential oil purity and adulteration.
- Hydrosols. A review describes hydrolates, or aromatic waters, as aqueous co-products of distillation that hold water-soluble volatile compounds. [3] They are not the same as the oil; see absolutes, hydrosols and infused oils.
Why this does not appear in a recipe here
Industrial distillation and solvent extraction use specialized equipment, and the review we read notes that traditional solvent extraction may involve toxic solvents. [3] Home-made oils and blends can also carry risks of their own; see Homemade blends and DIY products.
How this helps when reading a label
A label that names the botanical name, the plant part and the country may help you tell which method and plant are involved; see Reading an essential oil label. Making method does not prove an oil is safe or that it works. For the basics, start with What are essential oils?.
Frequently asked questions
Are all essential oils made by steam distillation?
No. A review says steam distillation is the most common method overall, but expression is most often used for citrus peels, and solvent extraction and enfleurage are also used. [1]
What is the difference between steam distillation and hydrodistillation?
In steam distillation only steam passes through the plant material. In hydrodistillation the plant material sits in boiling water. [3]
What is an absolute?
One 2026 review uses "absolute" for a product made with an organic solvent, such as a concrete or resinoid. It describes these as aromatic extracts, not classical essential oils, and says they may contain waxes, pigments and resins. [3] See absolutes, hydrosols and infused oils.
Why do some citrus oils need sun protection?
Pressed citrus peel oils can contain furocoumarins, which can cause reactions when treated skin meets UVA light. [1] The FDA flags certain citrus oils as potentially harmful on skin exposed to the sun. [5]
Can I distill essential oils at home?
We do not provide instructions. Published sources describe industrial equipment and, for solvent methods, possibly toxic solvents. [3] If you have a question about a product you already own, ask a pharmacist or poison center.
References
- Sharmeen JB, Mahomoodally FM, Zengin G, Maggi F. Essential Oils as Natural Sources of Fragrance Compounds for Cosmetics and Cosmeceuticals. Molecules. 2021 (review). Read 2026-10-23.
- Essential oils: Poisonous when misused, Poison Control (National Capital Poison Center), US. Article date not shown on the page. Read 2026-10-23.
- Youchret-Zallez OB and colleagues. Essential Oil Quality in Medicinal and Aromatic Plants: Linking Plant Biosynthesis, Matrix Selection and Extraction Strategy. Plants (Basel). 2026 (review). Read 2026-10-23.
- Pierson M, Fernandez X, Antoniotti S. Type and magnitude of non-compliance and adulteration in neroli, mandarin and bergamot essential oils purchased on-line. Scientific Reports. 2021. Read 2026-10-23.
- Aromatherapy, US Food and Drug Administration (FDA), content current as of 09/08/2023. Read 2026-10-23.