What Are Essential Oils?
What essential oils are, how sources define them, what research and regulators say, and the safety points to know first. The starting page for the whole Essential Oils library.
Content last updated . This page has not been medically reviewed.
Safety first. Natural products can cause side effects and interact with medicines. Read essential oil safety before you use anything on this page.
Safety first. Essential oils are concentrated, and misuse can cause serious poisoning. [1] This site never advises swallowing them. If someone has swallowed an essential oil, use a poison center's online tool or call Poison Help at 1-800-222-1222 (US), and call 911 for collapse, a seizure or trouble breathing. Start with Essential oils safety: start here and Essential oil safety.
Essential oils are concentrated plant extracts that keep the natural smell and flavor of their source. The US National Institute of Environmental Health Sciences (NIEHS) says they are obtained through mechanical pressing or distillation. [2] Each one has its own mix of chemicals, and that mix affects the smell, how it is absorbed and its effects on the body. [2] Aromatherapy is a separate idea: it is the use of essential oils from plants as a complementary health approach, most often by inhaling them or applying a diluted form to the skin. [3]
How sources define the term
Different sources draw the line in slightly different places, so it helps to know what is being described.
- NIEHS says synthetic oils are not considered true essential oils. [2]
- A 2026 review uses "essential oil" for a volatile plant product obtained mainly by hydrodistillation, steam distillation or mechanical expression. It calls products made with organic solvents "aromatic extracts" rather than classical essential oils; these include concretes and absolutes. [4]
- The FDA says there is no regulatory definition for "essential oils". [5] A product with that word on the label has not necessarily met any set standard.
Terms that are often mixed up with essential oils have their own pages: absolutes, hydrosols and infused oils, fragrance oils and carrier oils.
Where they come from and how they are made
The plant part used differs by oil: flowers for ylang ylang, leaves for peppermint and rosemary, peel for orange and lemon, wood for sandalwood, resin for myrrh and frankincense, according to one review. [6] A US poison center says essential oils are often extracted by pressing or steam distillation. [1] The detail, including solvent extraction, is on How essential oils are made.
What is in an essential oil
An essential oil is a mixture of many chemicals, and the mix can vary within the same plant species or from plant to plant. [2] A review notes that essential oils are hard to standardize because of variable growing conditions, genetics and harvesting. [6] This is why a result for one oil, plant part or batch cannot be assumed for another. See What is in an essential oil for the compounds.
Not the same as the herb, the tea or a supplement
An essential oil is not the herb it comes from, a tea or a capsule, and a result for one form does not carry over to another. For example, NCCIH says some combination products that include peppermint leaves may help relieve indigestion, but there is no evidence that peppermint oil taken alone can help. [7] The plant is covered under Herbs and Botanicals and the tea under Herbal Teas and Extracts.
Traditional use and what research shows
Traditional use. A US poison center says many essential oils have a long history of medicinal use based largely on traditional medicine practices and folklore. [1] That describes history. It is not evidence that an oil works, and it is not evidence that an oil is safe. The story of how these oils came to be used is on History of aromatherapy.
Research. Studies of essential oils in people are limited. The same poison-center article says few uses have been studied in a scientific way. [1] Some examples from NCCIH:
| Question | What the source found | Strength of evidence |
|---|---|---|
| Does aromatherapy help with insomnia? | NCCIH says it is sometimes used for insomnia, but it is not known whether it helps because little rigorous research has been done. [3] | Insufficient evidence |
| Do lemon or lavender scents change stress markers? | In one study of people under stress, lemon had a positive effect on mood, but neither scent affected stress indicators, immune-system markers or pain control. [3] | Mixed; one small study |
| Do enteric-coated peppermint oil capsules help irritable bowel syndrome (IBS)? | NCCIH describes a 2022 review of 10 studies (1,030 participants) in which peppermint oil beat placebo for overall IBS symptoms and belly pain, with more side effects such as acid reflux and indigestion. [7] These were pharmaceutical-type capsules tested in trials. This is not advice to swallow an oil. | Promising but limited |
| Does tea tree oil on the skin help acne or athlete's foot? | NCCIH says a small amount of evidence suggests it might help, but more studies are needed. [8] | Promising but limited |
Aromatherapy trials are often small and short, and it is hard to hide the smell from participants, so many measure self-reported feelings. The library's overview of the studies is on Essential oil research and evidence. We did not find a source we could read that supports the idea that an oil cures or prevents a disease, and this site does not claim that one does.
Natural does not mean safe
The FDA points out that many plants contain materials that are toxic, irritating or likely to cause allergic reactions when applied to the skin. [9] A US poison center lists the main concerns: [1]
- Skin. Rashes are possible, and not all essential oils are appropriate for use on the skin. [1]
- Allergy. Allergy to an essential oil is "a very real possibility". [1]
- Children. Children have thin skin and immature livers, which might make them more susceptible to toxic effects. [1]
- Medicines. Essential oils may also interact with medications. [1] Ask a pharmacist, and see How interactions work.
- Contents. It can be hard to know exactly what is in the bottle. [1] See Essential oil quality and labels.
Where to go next
- Find an oil by name: A to Z directory, or start with lavender, peppermint or tea tree.
- Groups of oils: lemon (citrus), geranium (floral), cedarwood (woody) and clove (spice).
- Practice: Aromatherapy and how oils are used, as sources describe.
- Goals: Essential oils by wellness goal and claims checked.
- People and pets: babies and children and pets.
- Terms and quick answers: glossary and frequently asked questions.
This site does not give recipes, blends or advice to swallow oils. Where research exists we describe it, and where it does not we say so.
Frequently asked questions
Are essential oils the same as aromatherapy?
No. Essential oils are the products. Aromatherapy is a practice that uses them as a complementary health approach, most often by inhaling them or applying a diluted form to the skin. [3]
Are essential oils safe because they are natural?
No. The FDA says many plants contain materials that are toxic, irritating or likely to cause allergic reactions on the skin. [9] A poison center says misuse of essential oils can cause serious poisoning. [1]
Is there an official definition of an essential oil?
The FDA says there is no regulatory definition for "essential oils". [5] Researchers and NIEHS describe them as concentrated plant extracts obtained by pressing or distillation. [2]
Do essential oils work?
It depends on the oil, the use and the form. For aromatherapy and insomnia, NCCIH says it is not known whether it helps. [3] For some specific uses, such as tea tree oil on the skin for acne and athlete's foot, NCCIH describes a small amount of promising evidence. [8] No source we read shows that an oil cures a disease.
Is a synthetic fragrance the same as an essential oil?
NIEHS says synthetic oils are not considered true essential oils. [2] The differences in labeling and safety are on Essential oils vs fragrance oils.
More details: evidence, limits and cautions
The details behind this page: cautions, limits of the evidence and where sources disagree. Open any note to read it.
What regulators say
In the US, how an aromatherapy product is regulated depends mainly on its intended use. [9] The FDA says claims that a product will relieve colic, ease pain, relax muscles, treat depression or anxiety, or help you sleep are drug claims. [9] It adds that cosmetics do not need FDA approval before they go on the market. [9] For more, see Who regulates essential oils?.
References
- Essential oils: Poisonous when misused, Poison Control (National Capital Poison Center), US. Article date not shown on the page. Read 2026-10-23.
- Essential Oils, National Institute of Environmental Health Sciences (NIEHS), page last reviewed March 19, 2026. Read 2026-10-23.
- Aromatherapy, National Center for Complementary and Integrative Health (NCCIH), last updated January 2020. 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.
- Fragrances in Cosmetics, US FDA, content current as of 02/28/2022. Read 2026-10-23.
- 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.
- Peppermint Oil: Usefulness and Safety, NCCIH, last updated May 2025. Read 2026-10-23.
- Tea Tree Oil: Usefulness and Safety, NCCIH, last updated April 2025. Read 2026-10-23.
- Aromatherapy, US Food and Drug Administration (FDA), content current as of 09/08/2023. Read 2026-10-23.