About 220 pounds of lavender make a pound of oil, which is why dilution matters

Key takeaways

• The National Cancer Institute says it takes about 220 pounds of lavender flowers to make about one pound of lavender essential oil³.
• University of Minnesota guidance treats one drop of oil in a teaspoon of carrier oil as about a 1% mix, a level it calls generally safe for massage, and says skin blends usually shouldn’t go above 5%⁵⁶.
• Pennyroyal tea has a long folk history, but the oil is roughly 80% to 85% pulegone, and NIH’s LiverTox says as little as a tablespoon can cause serious harm¹².
• European regulators say the benefits of sage essential oil don’t outweigh its risks, because its thujone can cause seizures¹².
• The FDA limited camphor in medicines to 11% in 1982 and banned camphorated oil, yet illegally imported camphor products later sent three Bronx toddlers to the hospital with seizures⁹¹⁰.

In 1979, doctors writing in JAMA described an 18-year-old who swallowed about an ounce of pennyroyal oil, hoping to end a suspected pregnancy¹. Two hours later she arrived at an emergency room with stomach pain, nausea and vomiting¹.

She kept getting sicker for almost two days. She bled heavily, her organs began shutting down, and she died about a week after taking the oil¹².

Pennyroyal is a mint, and folk healers have used it for at least 2,000 years¹. LiverTox, the National Institutes of Health’s database of drug- and herb-related liver injury, says the tea and leaf extracts have a largely clean safety record². Babies are the exception: in 1996, doctors reported two infants who developed organ failure after being given home-brewed mint tea made with pennyroyal, and one died¹². The oil is in another league².

That gap between a cup of tea and a spoonful of oil is the heart of essential-oil safety. Distilling a plant can turn a gentle remedy into a potent chemical mix.

This guide gives you the dilution math in plain drops, explains the handful of compounds behind many serious poisonings, and lists the oils that deserve extra respect.

A small bottle holds a field of plants

Essential oils often sit just under the surface of a plant’s leaves, bark or peel. Crushing the plant or passing steam through it releases the aromatic compounds³.

The yield is small. The National Cancer Institute (NCI) says it takes about 220 pounds of lavender flowers to produce about one pound of oil³. By our math, the oil is less than half of 1% of the flowers’ weight, so it carries the aromatic compounds of more than 200 times its weight in blossoms.

Form and route change how a plant behaves on the body. The FDA notes that cumin oil is safe in food but can blister skin, and that some citrus oils that are fine to eat can harm skin exposed to the sun⁴.

Pennyroyal shows the same pattern on the inside. Its oil is about 80% to 85% pulegone, a compound the liver converts into a second toxin that damages liver cells². By LiverTox’s account, a single tablespoon (15 milliliters) is enough to bring on seizures, coma or sudden liver injury².

The good news is that such cases are now rare. LiverTox notes that two large U.S. studies, one of 300 cases of drug-related liver injury and one of 85 cases tied to herbs and supplements, found no pennyroyal cases at all².

The dilution math fits on an index card

Dilution means mixing a few drops of essential oil into a “carrier,” usually a plain plant oil such as sweet almond, apricot kernel, grapeseed, jojoba or avocado⁶.

For skin, guidance on the University of Minnesota’s Taking Charge wellness site, written by nurse researcher Linda Halcón, says blends usually shouldn’t go above 5%⁵. Its how-to page puts the general ceiling at 3% to 5% and calls 1%, about one drop per teaspoon, generally safe for massage or large areas of skin⁶.

The National Association for Holistic Aromatherapy (NAHA), a professional and industry membership group, suggests lower strengths for the face. It lists 0.5% to 1% for sensitive skin and 1% to 2.5% for normal facial skin, for adults only⁷.

Children need less. The Minnesota guidance suggests 0.25% for infants, 0.5% from 6 months to 2 years, and 1% from age 2⁶. A Johns Hopkins pediatrician, Rachel Dawkins, describes 0.5% to 2.5% for children depending on age and weight, citing a standard safety textbook whose ranges start at a fraction of a percent for babies and rise with age⁸.

Inhaling oils needs moderation, too. The Minnesota site advises short sessions, 15 minutes or less in any hour⁵.

Some oils burn even when they’re diluted

Dilution is the main defense against skin trouble. Poison Control calls a carrier oil the best protection against a reaction where oil touches skin, and it warns against putting oils on broken or damaged skin¹¹.

But dilution has limits. Some oils that are pleasant to breathe in can still sting skin in a 3% to 5% blend; the Minnesota guidance names thyme, oregano, clove and cinnamon bark⁵.

Thyme oil is the sharpest example. The Tennessee Poison Center at Vanderbilt says its main compound, thymol, is corrosive and can cause serious chemical burns, and because thymol also numbs, those burns may not hurt at first⁹.

Using an oil “neat,” meaning undiluted, adds risk. Johns Hopkins warns that undiluted oil added to a bath can still irritate skin in its concentrated form, so dilute it first, and keep oils clear of the eyes, ears and nose⁸. Our companion article on swallowed and skin-applied oils covers burns, sun reactions and first aid in detail.

Five groups of compounds to know by name

Each essential oil gets its scent, its effects and its dangers from one or more key compounds⁹. A few of those compounds account for the poisonings described in this article, and knowing their names helps you spot risky oils.

Pulegone: the liver toxin in pennyroyal

Pulegone drains glutathione, one of the liver’s main protective molecules, and its breakdown product injures liver cells². Poisonings can bring seizures, bleeding, liver and kidney failure and death¹².

LiverTox suggests that doctors give N-acetylcysteine, much as they would for an acetaminophen overdose². Poison Control’s article says there is no antidote, so the two sources differ. Either way, prevention matters most¹.

Thujone: the seizure trigger in sage and wormwood

Thujone occurs in sage, wormwood, tansy and cedar leaf, among others¹². The European Medicines Agency’s herbal committee says its most prominent acute effect is seizures, and overdoses can cause unconsciousness and death¹².

The committee recommended a limit of 6 milligrams of thujone a day from an herbal medicine. It advised keeping use by children and pregnant women to a minimum, and it concluded that the benefits of sage essential oil don’t outweigh its risks¹². Poison Control reports that children have had seizures after swallowing only a little sage oil¹¹.

Camphor: the reason the FDA set a ceiling

Camphor can trigger seizures within minutes of being swallowed¹¹. In 1982, the FDA limited camphor in medicines to 11% and banned camphorated oil, a 20% product, after deaths⁹¹⁰. According to the Tennessee Poison Center, a teaspoon of camphorated oil has killed children⁹.

The rule didn’t end the problem. Over two weeks, a children’s hospital in the Bronx treated three toddlers, aged 15 to 36 months, for camphor seizures¹⁰. All three needed drugs to stop the seizures, and one child was poisoned by repeated rubbing on the skin, not swallowing¹⁰.

The camphor came from imported products sold illegally and used as a natural remedy, for colds, for spiritual purposes or against pests¹⁰.

1,8-cineole and menthol: risky for small children

Eucalyptus oil’s chief troublemaker is eucalyptol, also called 1,8-cineole⁹. Swallowed, the oil can cause seizures, Poison Control warns¹¹. Our companion article on swallowed oils describes three children who had seizures after their first dose.

Peppermint’s menthol has stopped young children’s breathing, the Minnesota guidance warns⁵. Experts disagree on the age cutoff. Johns Hopkins says to avoid peppermint before 30 months because of seizure risk, while Minnesota says to avoid it under age 6⁵⁸. Our peppermint article explains why menthol and babies’ faces don’t mix.

Estragole and methyl eugenol: a slower worry

Some compounds raise long-term questions rather than emergencies. In a 2005 statement, Europe’s herbal committee called estragole a naturally occurring genotoxic carcinogen, meaning it damaged DNA and caused liver tumors in mice¹³.

Sweet basil oil can be 5% to 85% estragole, and fennel oil can range from under 1% to over 80%¹³. The committee judged short-term adult use at normal doses not to be a significant cancer risk, but it urged keeping exposure low in young children and in pregnant or breastfeeding women¹³.

The FDA reached a related legal conclusion in 2018. It removed six synthetic flavorings, including methyl eugenol and pulegone, from its list of approved food additives because high doses caused cancer in lab animals¹⁴. The agency stressed that the small amounts used in food posed no public health risk, and that natural flavors containing these compounds were unaffected¹⁴.

Oil	Key compound	Main concern	Handle it this way
Pennyroyal	Pulegone	Liver failure, death12	Don’t swallow or use as a remedy1
Sage, wormwood	Thujone	Seizures1112	Avoid sage oil; minimize for children and pregnancy12
Camphor	Camphor	Seizures within minutes911	Keep away from children; skip illegally sold imports10
Eucalyptus, peppermint	1,8-cineole, menthol	Seizures if swallowed; menthol has stopped young children’s breathing5811	Lock up; no peppermint for young children58
Basil, fennel	Estragole	Cancer in mice13	Short-term use; minimize for children, pregnancy, breastfeeding13
Thyme, oregano, clove, cinnamon bark	Thymol and other irritants	Skin irritation; thyme can burn59	Keep skin blends low or skip skin use5
Bergamot, lime, lemon, orange	Sun-reactive compounds	Skin reactions in sunlight45	No sun or tanning beds after skin use5

Wintergreen also belongs on any danger list, because it contains methyl salicylate, a chemical cousin of aspirin⁹. Our lavender sleep article covers its poisoning risk and packaging rules.

Old oil is a different oil

Essential oils change in the bottle. NCI notes that their chemical makeup shifts as they age, and many oils carry no expiration date³.

That matters for skin. Stale or chemically changed oils irritate skin more often, according to the Minnesota guidance⁵. Our article on lavender explains how air exposure can turn common oil compounds into skin allergens.

Simple habits help. Store bottles like medicine, out of children’s reach and out of direct sun, in a cool, dry spot, as Johns Hopkins advises⁸. Carrier oils go rancid too; Minnesota suggests refrigerating them, expecting about a year of use, and throwing them out if they smell off⁶.

“Therapeutic grade” is a sales term, not a standard

Some bottles promise “therapeutic grade” or similar quality labels. Those are seller’s terms. We found no federal standard behind them: the FDA’s aromatherapy page describes no quality grades, and the agency has no rules defining even “natural” or “organic” for cosmetics⁴.

What the FDA does say is that every cosmetic ingredient must meet the same safety requirement, whatever its source⁴. A plant origin earns no special pass.

Johns Hopkins suggests choosing companies that print the oil’s botanical (Latin) name and origin and give you a way to contact them⁸. A Latin name matters because one common name can cover more than one plant: pennyroyal oil can come from two different mints². Our articles on third-party testing and certification logos explain what outside checks can and can’t confirm.

What the evidence shows

Claim	Evidence rating	What it rests on
Pennyroyal oil is a safe home remedy	Evidence says no, or unsafe	Case reports over more than a century; LiverTox rates it a likely cause2
Sage and wormwood oils are safe to take by mouth	Evidence says no, or unsafe	European regulatory review and poisoning reports1112
Camphor products are safe around small children	Evidence says no, or unsafe	Case series and the FDA’s 1982 limit910
Specific limits, such as 1% to 5%, are the right cutoffs for adult skin	Not enough evidence	Professional and university guidance and experience, not head-to-head trials; sources differ on exact numbers5678
Estragole-rich oils raise cancer risk in people	Not enough evidence	Mouse studies; no human proof; regulators advise caution13
“Therapeutic grade” means better or safer oil	Not enough evidence	No federal grading standard; the FDA’s aromatherapy page describes none4

Respecting the plant means respecting the dose

Herbal traditions have always taught that preparation matters. A tea, a poultice and a distilled oil are three different medicines, even from one plant.

Natural-health values fit well with dilution. Using fewer drops costs less, spares the plants it takes to make each bottle, and keeps the experience gentle. Treat essential oils the way an experienced herbalist treats any strong plant: with knowledge, small amounts and patience.

When something goes wrong, act fast. Call Poison Control at 1-800-222-1222, the line for the nation’s 53 poison centers¹⁵. Call 911 right away for a seizure, collapse, trouble breathing or someone you can’t wake¹⁵.

Questions readers ask

The bottom line

Essential oils are plants distilled to a fraction of their size, and that strength is why they need care. For skin, the guidance we reviewed starts around 1% for large areas, goes lower for children and the face, and rarely exceeds 5%. One drop per teaspoon of carrier is a useful anchor.

A handful of compounds, including pulegone, thujone, camphor and the 1,8-cineole and menthol in eucalyptus and peppermint, account for many serious poisonings. Keep those oils away from children, never swallow pennyroyal or sage oil, and store every bottle like medicine.

Keep exploring: essential oils and cats.

Related reading

• What poison centers see when essential oils are swallowed or used neat
• Lavender is the best-studied sleep scent, though its trials can’t hide the smell
• Lavender can mean several plants, and beyond anxiety capsules the evidence is thin
• Peppermint oil has the trials, but the tea most people drink doesn’t
• Nature makes both medicine and deadly poison, and respecting it means telling them apart

Sources

1. Mekonnen S. “Pennyroyal Oil: A Potentially Toxic Folk Remedy.” National Capital Poison Center (Poison Control), accessed October 2026. poison.org
2. National Institute of Diabetes and Digestive and Kidney Diseases. “Pennyroyal Oil.” LiverTox: Clinical and Research Information on Drug-Induced Liver Injury, NIH, updated March 28, 2020. ncbi.nlm.nih.gov
3. National Cancer Institute. “Aromatherapy With Essential Oils (PDQ®)–Patient Version.” NIH, updated September 11, 2023. cancer.gov
4. U.S. Food and Drug Administration. “Aromatherapy.” FDA, content current as of September 8, 2023. fda.gov
5. Halcón L (contributor), Maher K (reviewer). “Are Essential Oils Safe?” Taking Charge of Your Wellbeing, University of Minnesota, accessed October 2026. takingcharge.csh.umn.edu
6. Halcón L (contributor), Maher K (reviewer). “How Do I Choose and Use Essential Oils?” Taking Charge of Your Wellbeing, University of Minnesota, accessed October 2026. takingcharge.csh.umn.edu
7. National Association for Holistic Aromatherapy (professional and industry membership group). “Methods of Application.” NAHA, accessed October 2026. naha.org
8. Johns Hopkins Medicine. “Are Essential Oils Safe for Children?” (with Rachel Dawkins, MD, Johns Hopkins All Children’s Hospital). Accessed October 2026. hopkinsmedicine.org
9. Loden J, Seger D. “What are the commonly used but potentially toxic essential oils?” Tennessee Poison Center, Vanderbilt University Medical Center, May 3, 2016. vumc.org
10. Khine H, Weiss D, Graber N, Hoffman RS, Esteban-Cruciani N, Avner JR. “A cluster of children with seizures caused by camphor poisoning.” Pediatrics, 2009;123(5):1269-1272 (Mount Sinai record). scholars.mssm.edu
11. Soloway RAG, Troutman WG. “Essential oils: Poisonous when misused.” National Capital Poison Center (Poison Control), accessed October 2026. poison.org
12. European Medicines Agency, Committee on Herbal Medicinal Products. “Public statement on the use of herbal medicinal products containing thujone.” EMA/HMPC/732886/2010 Rev.1, adopted May 22, 2012. ema.europa.eu
13. European Medicines Agency, Committee on Herbal Medicinal Products. “Public statement on the use of herbal medicinal products containing estragole.” EMEA/HMPC/137212/2005, November 2005. ema.europa.eu
14. U.S. Food and Drug Administration. “FDA Removes 7 Synthetic Flavoring Substances from Food Additives List.” Constituent update, October 5, 2018. fda.gov
15. America’s Poison Centers. “Poison Help.” PoisonHelp.org, accessed October 2026. poisonhelp.org