Dilution, hot oils, sunlight, children, animals and the shelf — the page every other lesson defers to.
~14 min read
Nothing here is written to make you nervous. An essential oil is not a herb, a tea or a lotion, and handling it as though it were is the mistake behind almost every unpleasant experience people have with these bottles. One drop of peppermint carries about as much of the plant’s volatile fraction as twenty-eight cups of peppermint tea.
A still carries off one narrow fraction and leaves the rest behind, so what reaches the bottle has nothing to buffer it. Wild orange is 80 to 97% limonene, cassia 75 to 97% cinnamaldehyde, clove 70 to 90% eugenol. What essential oils are covers that fraction.
So this asks for respect rather than fear. Aromatic use is the mildest route; topical use is where dilution matters, and where most of this lesson lives; internal use is the narrowest and depends on your own label. How to use oils is the method lesson.
Diluting in a carrier is not only a safety measure — it improves absorption and extends contact time. Fractionated coconut oil is the commonest carrier and suits every age.
| Who | Strength | Per 10 mL | Per 30 mL | Note |
|---|---|---|---|---|
| General adult use | 2% | 4 drops | 12 drops | Standard daily use |
| Sensitive adults and the elderly | 1% | 2 drops | 6 drops | Reduced concentration |
| Children 2–10 years | 0.5–1% | 1–2 drops | 3–6 drops | Always dilute |
| Children under 2 | Ask a healthcare practitioner | — | — | No figure is printed here |
| Hot oils, all ages | 0.5% or less | 1 drop | 3 drops | Oregano, cassia, cinnamon bark, clove, thyme |
A drop is not a unit of measurement — it is whatever the reducer and the oil’s thickness produce. This platform works at roughly twenty drops to the millilitre, and every drop count in the curriculum uses that rate. A thick oil such as myrrh drops larger, so the same count is a higher percentage.
Where a drop count and a percentage disagree, follow the percentage. The percentage is the instruction; the drop count only approximates it.
A drop-to-drop figure on a bottle — one drop in at least ten drops of carrier — is roughly 9%, and answers a different question: one spot on thick skin, once. A percentage is for a blend spread over an area, used repeatedly, or left on. When unsure, use the percentage.
Diagram to come
A conversion chart that removes the arithmetic. Left column: four strengths as vertical bars of increasing height — 0.5%, 1%, 2%, 3%. Middle and right columns: for each strength, a row of drawn, individually countable drop symbols for a 10 mL bottle and for a 30 mL bottle, at twenty drops to the millilitre. The drops must be countable rather than written as numerals, so the tripling between 10 and 30 mL is visible at a glance. A single line across the foot notes that a thicker oil gives a larger drop. No body outlines, no product bottles — this is a ruler, not an illustration.
The older version of this page gave 2% as “1 drop per 5 mL” and 1% as “1 drop per 10 mL”. Those counts assumed ten drops to the millilitre — half what a standard reducer gives. At twenty drops, 2% is two drops in 5 mL, not one. The percentages in the table are unchanged; only the conversion has been settled, and anyone following the older counts was working at about half strength.
The part people get backwards first: dilution usually makes an application work better, not worse. Most of a neat drop on warm skin leaves as vapour within minutes rather than crossing into you. A carrier is not volatile — it holds the constituents against the surface and spreads them wider, so concentration at any one point falls while the total crossing can be as high or higher. Skin and hair works through the barrier.
Only consume oils explicitly labelled for internal use. That is the entire rule, because labelling differs across the 65 markets and your bottle is the only authority. Where a market permits it, doTERRA marks those oils with a Supplement Facts panel; where it does not, the same oil carries no panel and the answer there is no.
Tea tree is labelled not for internal use in every market. Wintergreen is labelled toxic if swallowed — over 98% methyl salicylate, the highest single-constituent concentration on the shelf.
Hot oils create a marked warming or tingling on skin and can irritate it if not heavily diluted. This list does not change:
Hot does not mean warm — nothing burns when the drop lands. Hence their own row in the table: half a per cent or less in any blend that covers an area or is used repeatedly — one drop in 10 mL, three in 30 mL. For a single spot, once, the bottle’s own minimum applies instead: one drop in at least ten drops of carrier, on the sole of a foot. Never on the face or neck, never near mucous membranes, never on a young child, never in a bath. Oregano has the rest.
If a drop lands neat: carrier oil, never water
Reach for fractionated coconut, olive oil, whatever fat is nearest, and apply it generously until the sensation settles. Do not go to the tap. Water does not dissolve these compounds — it pushes the drop outward across more skin without carrying any of it away, so the sensation spreads instead of easing.
Five of the six share a chemistry. Oregano and thyme are dominated by the phenols carvacrol and thymol; cassia, cinnamon bark and clove by phenylpropanoids — cinnamaldehyde at 75 to 97% in cassia, 45 to 80% in cinnamon bark, eugenol at 70 to 90% in clove. Lemongrass is the honest edge of the list: not a phenol oil, but 25 to 50% neral and 25 to 50% geranial, the two halves of citral. Citral is a well-documented skin sensitiser, which is why many lists group lemongrass with the hot oils, though our own oil pages mark it Sensitive rather than Dilute. Functional group families sets out the families.
Receptors on the nerve endings in your skin — the same ones that report genuine heat — are opened directly by these molecules, so the nerve fires the signal it always fires and your brain receives heat. Capsaicin in a chilli works the same way. Underneath the sensation, a phenol at high local concentration is disturbing the lipid mortar that holds your outer skin layer together, which is irritation rather than signalling.
A water molecule is lopsided: its oxygen pulls the shared electrons towards itself, leaving one end slightly negative and the hydrogen ends slightly positive. That charge separation is polarity. Carvacrol, eugenol and cinnamaldehyde carry at most a small polar patch on a large, flat, non-polar ring, so they are fat-soluble and water has nothing to offer them. Tip water onto a neat drop and the oil is pushed ahead of it — a wider footprint, the same compound, more nerve endings recruited. A carrier oil is the same kind of substance, so it takes the constituents into solution and spreads them through its own volume. Rinsing never does that.
Citrus oils pressed from the peel carry furanocoumarins — compounds that react with ultraviolet light and can darken or burn the skin they were applied to. The rule is not negotiable: after applying an expressed citrus oil, keep that skin out of direct sunlight and off sunbeds for twelve hours.
Tangerine, green mandarin and white grapefruit carry the same caution. To recognise one without a list, read how it was made: cold pressed or expressed from peel, and the rule applies; steam distilled, and it does not. Furanocoumarins will not travel with steam — so a distilled lime does not carry the risk, and nor does bergamot FCF. Lemon has the fuller picture.
Nothing happens at the moment of application, and nothing in shade. The result appears hours later, in the exact shape the oil was applied in, and it can be a genuine burn, with darkening that lasts months.
Diagram to come
A twelve-hour timeline running left to right, marked at application, +2h, +6h and +12h, with everything before +12h shaded as the window in which sun is avoided and everything after it clear. Above the timeline, two forearms side by side: one in shade, unmarked; one in sunlight showing a reaction in the exact stripe shape the oil was applied in, drawn at the later end of the timeline rather than at application. To one side, a key of two bottle icons — one cold pressed with the rule applying, one steam distilled with it not applying. No legible product labels.
When ultraviolet light reaches skin still carrying furanocoumarins, those molecules absorb the energy and become reactive in a way they never are in the dark. That delay is why the reaction does not arrive when you expect it.
Furanocoumarins are flat, three-ringed molecules — bergapten is the one usually named. Flatness is the problem: a flat molecule slides between the stacked base pairs of DNA inside a skin cell and sits there doing nothing, which is what it does in the dark. Ultraviolet A light, around 320 to 400 nanometres, is absorbed by that ring system and lifts the molecule into an excited state, in which it forms bonds it never would otherwise — to the DNA it rests against, and to nearby proteins. The cell registers serious damage, and the visible result behaves like a burn, arriving with the delay such a response takes. These molecules are non-volatile, so they do not evaporate away — hence twelve hours rather than twenty minutes.
These are not matters of degree: no concentration makes them acceptable, no oil is an exception.
Eyes
Nothing, ever, at any dilution — not the eyelid, not the brow bone, not the skin around the socket. Oil migrates, and vapour rises into an open eye.
Inner ears
Nothing goes into an ear canal. Apply diluted behind the ear instead.
Broken skin
Cuts, grazes, cracked skin, sunburn, a healing wound. No barrier, so absorption is unpredictable and the sting is real.
The face of a young child
Nothing on the face or neck of a child under six. Not a question of dilution but of breathing, below.
Mucous membranes
Inside the nose or mouth, or any other mucous surface. No keratinised barrier, which is why a drop that only stings on a forearm does real damage in a nostril.
A bath, without a carrier
Dropped into a bath, oil floats as neat droplets and meets skin undiluted. Stir it into a tablespoon of carrier first.
Diagram to come
A plain full-body outline, front-facing, neutral and ungendered, with each excluded site marked by a simple exclusion symbol and a short leader line to its label: eyes, inner ears, inside the nose and mouth, and broken skin shown as a small mark on a forearm. Beside the adult, a clearly smaller child figure with its face and neck marked. The soles of the feet are marked differently, as the site oils are most often placed instead. No shading, no anatomical detail, one accent colour only; it must be readable at phone width in one glance.
A child is not a small adult. Children’s skin is more permeable, and a child carries far more skin area per kilogram of body weight — a newborn roughly three times an adult’s — so the same drop is a much larger dose. The rule is half the adult dilution or less: 0.5 to 1% between two and ten, one to two drops in 10 mL or three to six in 30 mL. Under two, this platform prints no figure. Ask a healthcare practitioner, and mean it.
Three oils stay away from the face and neck of a child under six: peppermint, eucalyptus and rosemary. Peppermint is 30 to 50% menthol; eucalyptus and rosemary are both dominated by 1,8-cineole. Near a small child’s nose or mouth, those compounds can cause a reflexive change in breathing. It is proximity to the airway that matters. Peppermint says the same.
Start a child on lavender, frankincense or Roman chamomile, all well diluted. The safest aromatic method is a diffuser in a ventilated room, briefly, door open. Every bottle lives out of reach: a reducer is not a child-resistant closure.
If a child swallows an essential oil, ring your poison centre now
Not later, not after watching for symptoms, not after searching for what that oil does. Ring your local poison control centre or emergency number immediately, with the bottle in your hand so you can read them the name. Do not make the child sick — bringing an oil back up takes it past the airway a second time. Do not force water through. The margin between a taste and a serious quantity is small, and the people on that number will tell you in seconds whether you have a problem.
Every situation here defers to a healthcare practitioner who knows the person. If you are pregnant or nursing, under medical care, or taking any medication, ask first.
In pregnancy, use oils with caution and speak to your practitioner before any topical or internal use. Aromatic use — a diffuser in a ventilated room — is generally considered the gentlest route. The oils conventionally set aside are those high in ketones, which includes camphor, sage and rosemary, along with those traditional practice has long avoided in pregnancy. Fennel’s own label says to avoid it in pregnancy.
Medication is the case people skip and the one that most deserves the question. Ask your prescriber or pharmacist rather than guessing. The same applies to anyone living with an ongoing condition, which is why no condition is named anywhere in this curriculum as something an oil addresses. What you do at home with plants is different from professional medical care and does not replace it.
Pets share your air and cannot say no to it, and are not scaled-down versions of you.
Cats
Cats clear phenols and monoterpenes far less readily than dogs and people do, so compounds that pass through you can linger in a cat. Oregano, thyme, cinnamon, clove and the citrus oils are most often named as unsuitable around them. Never apply an oil to a cat.
Dogs
A dog’s nose carries in the order of forty times the scent receptors yours does, so a diffuser pleasant at your height is stronger at theirs — and a dog cannot open the door. Watch whether the dog leaves the room.
Birds
The most sensitive animals in any house to anything airborne: their lungs pass air through in one direction, extracting far more of whatever is in it. Do not diffuse where a bird lives.
Small caged animals
Rabbits, guinea pigs, rodents and reptiles: small body, fixed enclosure, no way to walk away.
The common mistake is not a drop on a paw but a diffuser running in a closed room with an animal that cannot leave. Diffuse with the door open, keep sessions short, and if your pet is under veterinary care, ask the vet first.
Four things degrade an essential oil: heat, light, air and time; the first three are what you control. The rules are short — a cool, dark place, lids closed tightly so the volatile compounds cannot escape, out of reach of children, citrus oils in the fridge. Which makes the shelf above the hob the worst place in the house, and where many people keep them: rising heat whenever you cook, and a warm-and-cool cycle that draws air in and out of the bottle.
An oxidised oil is not a faded version of a fresh one but a different mixture, and the difference runs the wrong way for skin: oxygen turns the lightest constituents into new compounds, several of which irritate far more readily than the ones they replaced. A bottle open three years in a sunny kitchen is more likely to cause a reaction than one opened last week, at the same dilution. Age is a safety variable, not only a quality one.
How you can tell
The smell goes flat first, then turns sharp and faintly like turpentine. The oil thickens and may go cloudy; the reducer becomes sticky.
Roughly how long
Citrus oils one to two years from opening, most others two to four, the heavy woods and resins many years — following from storage, not a date on the bottle.
What to do with an old one
Retire it from skin. An oxidised citrus oil is still useful in a surface spray, where contact is brief and rinsed, but not in anything left on.
Photograph to come
An open cupboard in a real domestic kitchen holding a dozen or so dark amber bottles upright in a plain wooden box or simple rack, caps on. Natural light falling into the room but not onto the shelf — the contrast between the lit room and the shaded cupboard is the subject. Softly out of focus in the background, a hob with a pan on it and the shelf directly above it, empty. No legible product labels, no styling, no props arranged for effect.
The oils that go first are the monoterpene-rich ones, because monoterpenes are the smallest and most reactive constituents on the shelf — the citrus oils above all, wild orange at 80 to 97% limonene, grapefruit at 90 to 97%, lemon at 60 to 75%, with the conifers and tea tree behind them. Sandalwood, patchouli, vetiver and myrrh are sesquiterpene-rich and keep for years.
A monoterpene is ten carbons and a couple of double bonds, and a double bond is where a molecule is most willing to react. Limonene has two; alpha-pinene has one held in a strained ring. Left in contact with air, oxygen attacks at those points and builds hydroperoxides — the same reaction that turns cooking oil rancid. Light supplies energy, warmth raises the rate, and each new hydroperoxide starts the reaction again in a neighbouring molecule, so it accelerates. A part-full bottle holds more air and ages faster for that alone. Limonene itself is mild on skin; limonene hydroperoxides are among the better-documented skin sensitisers in fragrance materials. Purity and quality covers what was in the bottle to begin with.
Read this once now, while nothing is happening.
Two habits prevent most of this. Patch test anything used regularly: mix it at final strength, put a coin-sized amount inside a forearm, leave it unrinsed, and check at 24 hours and again at 48. And introduce one oil at a time. The bathroom covers leave-on products.
Keep oils away from eyes and inner ears, and out of reach of children. If you are pregnant, nursing, under medical care or taking medication, speak to your healthcare practitioner before use. Nothing here is intended to diagnose, treat, cure or prevent any disease.
Lesson 8 of 21 · Essential Oils