How to check an essential oil blend
To check an essential-oil blend, work out each oil's own concentration in the finished bottle and compare it against that oil's published maximum dermal level — then check the blend against the person and pets it will be around. Most free calculators only give you a single overall percentage, which is why a blend can look fine at 2% while one ingredient inside it sits ten times above its own limit. The analyzer above does both: it computes the per-oil percentages, checks them against the database, and grades the result out of 100.
Three blends, analyzed
Here are three real blends run through the analyzer — the same engine, the same numbers you get if you open each one. The first is within every limit; the other two look ordinary but fail on a single oil, which is exactly the kind of problem a single overall percentage hides.
A calming evening roller — within every limit
Adult · Roller (10 ml) · 2.5% total dilution
One oil from each note layer, kept under both the adult ceiling and each oil’s own limit. This is the shape of a blend that grades well.
| Oil | In this blend | Published max | Verdict |
|---|---|---|---|
| Lavender | 1% | no specific limit | No limit exceeded |
| Cedarwood (Atlas) | 0.5% | 5% | No limit exceeded |
| Bergamot (FCF) | 1% | no specific limit | No limit exceeded |
Verdict: A well-built Fresh Floral.
Open this blend in the analyzerA tame-looking 2.5% blend that still fails — on one oil
Adult · Roller (10 ml) · 2.5% total dilution
The overall dilution looks perfectly normal, but a single drop of cinnamon bark sits many times over its own published maximum. This is the per-oil check most calculators skip.
| Oil | In this blend | Published max | Verdict |
|---|---|---|---|
| Sweet Orange | 1.5% | 12% | Flagged: oxidation risk. |
| Clove Bud | 0.5% | 0.5% | Flagged: phenol, skin sensitizing, dermal irritant, blood thinner. |
| Cinnamon Bark | 0.5% | 0.07% | Cinnamon Bark is at 0.5% here — above its published 0.07% dermal maximum. Flagged: dermal irritant, skin sensitizing, phenol. |
Verdict: Oriental Citrus — but the dilution needs fixing before skin use.
The one change worth making: Take Cinnamon Bark out of this blend — Its published maximum is 0.07%, so even a single drop overshoots a 10 ml bottle — you'd need about 72 ml of carrier for one drop. Leave it out here, or save it for a much larger batch or a diffused blend.
Open this blend in the analyzerA citrus roller that would burn in sunlight
Adult · Roller (10 ml) · 2.5% total dilution
Cold-pressed bergamot is phototoxic. On a leave-on skin blend above its limit, the analyzer flags the sunlight risk a plain percentage would never surface.
| Oil | In this blend | Published max | Verdict |
|---|---|---|---|
| Bergamot (Non-FCF) | 1% | 0.4% | Bergamot (Non-FCF) is at 1% here — above its published 0.4% dermal maximum. Phototoxic above 0.4% on skin exposed to sunlight — it's at 1%. Keep it lower, or use it in a rinse-off or diffused blend. |
| Lavender | 1% | no specific limit | No limit exceeded |
| Vetiver | 0.5% | 10% | No limit exceeded |
Verdict: Fresh Floral — but the dilution needs fixing before skin use.
The one change worth making: Take Bergamot (Non-FCF) out of this blend — Its published maximum is 0.4%, so even a single drop overshoots a 10 ml bottle — you'd need about 13 ml of carrier for one drop. Leave it out here, or save it for a much larger batch or a diffused blend.
Open this blend in the analyzerWhat the analyzer checks
- Per-oil dermal limits. Each oil's concentration in your bottle against its own published maximum — the check that catches cinnamon bark, clove, oakmoss and lemongrass in otherwise ordinary-looking blends.
- Phototoxicity. Cold-pressed citrus oils have their own sunlight limits on leave-on skin products; the analyzer applies them only where they actually matter.
- Who it's for. Adult, child, infant, pregnancy and elderly ceilings, plus oils individually flagged unsuitable for those groups.
- Cats and dogs. Per-oil suitability for the animals in your home — a check no free web tool offers.
- Structure and evolution. Top/heart/base balance, the fragrance family your blend resolves to, projection and longevity, and a timeline of how it changes over the hours after application.
How the grade works
Each blend gets a score out of 100 — safety is worth half of it (50 points), then balance (25), structure (15) and character (10). The letter is always paired with a plain verdict, and the bands mean something specific: aD or an F means something was flagged — an exceeded limit, a restricted material, an over-dosed diffuser, or an oil that doesn't suit the person or pets you selected. Because the letter combines craft with safety, the safety verdict shown above it is the line to read for safety.
| Grade | Score | What it means |
|---|---|---|
| A — Nothing flagged | 90–100 | This check found no issue, and the structure is balanced. It is not a guarantee of safety — see what the check does and doesn’t cover. |
| B — Minor notes | 80–89 | Nothing exceeded a limit. Either an oil carries a caution, or the structure could be tightened. |
| C — Worth refining | 70–79 | No limit exceeded, but the balance or structure is off — typically a missing note layer or one oil dominating. |
| D — Issues to resolve | 60–69 | Something is flagged — a limit exceeded, a restricted material, an over-dosed diffuser, or an oil unsuitable for the person or pets you selected. |
| F — Do not use as written | below 60 | Several findings, or a serious one. Resolve the flagged items before this goes on skin. |
Safe dilution at a glance
| Who it’s for | Body | Face | Bath |
|---|---|---|---|
| Adult | 3% | 1% | 2% |
| Child (2–6) | 2% | Not recommended | 1% |
| Infant (3–24 months) | 0.5% | Not recommended | Not recommended |
| Pregnancy | 1% | 0.5% | 1% |
| Elderly / sensitive skin | 1% | 0.5% | 1% |
Each oil's own limits are also listed on its page in the oil library.
Essential oils with the strictest dilution limits
A small number of oils have very low published dermal maxima — the ones most likely to push an otherwise-ordinary blend over the line. These are ceilings for leave-on skin, not targets; on the face, and for children or in pregnancy, keep well below them. Of the 225 materials in the library, these carry the tightest limits:
| Oil | Aroma family | Max on skin (body) |
|---|---|---|
| Massoia Bark | woody | 0.01% |
| Tagetes (Marigold) | herbaceous | 0.01% |
| Elecampane | herbaceous | 0.03% |
| Fig Leaf Absolute | green | 0.05% |
| Cinnamon Bark | spicy | 0.07% |
| Lavender Absolute | floral | 0.1% |
| Oakmoss Absolute | earthy | 0.1% |
| Tarragon | herbaceous | 0.1% |
| Treemoss Absolute | earthy | 0.1% |
| Calamus / Sweet Flag | spicy | 0.12% |
| Clary Sage Absolute | herbaceous | 0.25% |
| Thuja / Cedar Leaf | woody | 0.25% |
| Bergamot (Non-FCF) | citrus | 0.4% |
| Cumin | spicy | 0.4% |
| Peru Balsam | resinous | 0.4% |
The phototoxic essential oils — the complete list
Only 15 oils in the library carry a phototoxic (sunlight) limit — almost all cold-pressed citrus. Kept below the limit they're fine on skin; above it, they can cause burns or lasting dark patches on skin later exposed to sunlight or UV. Steam-distilled and FCF (bergapten-free) versions are not phototoxic. This is the full set:
| Oil | Aroma family | Max on sun-exposed skin |
|---|---|---|
| Fig Leaf Absolute | green | 0.01% |
| Tagetes (Marigold) | herbaceous | 0.01% |
| Bergamot (Non-FCF) | citrus | 0.4% |
| Cumin | spicy | 0.4% |
| Celery Seed CO2 | herbaceous | 0.5% |
| Lovage Root | herbaceous | 0.5% |
| Lime (Cold Pressed) | citrus | 0.7% |
| Angelica Root | earthy | 0.8% |
| Bitter Orange | citrus | 1.25% |
| Citron | citrus | 2% |
| Lemon (Cold Pressed) | citrus | 2% |
| Grapefruit (Pink) | citrus | 4% |
| Grapefruit (White) | citrus | 4% |
| Pomelo | citrus | 4% |
| Yuzu | citrus | 4% |
See the full phototoxic oils reference for detail on each.
Working the other way round?
If you know the strength you want and need the drop count, the Dilution Calculator converts any percentage into drops for roller bottles, sprays, diffusers, baths and more — sized to who it's for.
Open the dilution calculatorFrequently asked questions
How do I know if my essential oil blend is safe?
Check each oil individually, not just the total dilution. Every oil has its own published maximum dermal level — cinnamon bark is about 0.07%, clove around 0.5%, while many oils have no specific restriction. A blend can sit at a normal 2% overall and still hold one oil far above its own limit. The Blend Analyzer works out each oil’s concentration in your bottle and compares it against that oil’s published maximum, then layers on pregnancy, child, cat and dog suitability.
What does the A to F blend grade mean?
The letter is a blend-quality score out of 100 that combines safety with scent structure, and it is always shown with a plain-language verdict. A means nothing was flagged and the structure is balanced; B means nothing exceeded a limit but there is a caution or a structural weakness; C means no limit was exceeded but the balance is off; D and F mean something was flagged — a limit exceeded, a restricted material, an over-dosed diffuser, or an oil unsuitable for the person or pets selected. Because the letter mixes craft with safety, the separate safety verdict shown above it is the line to read for safety. Neither is a guarantee: the check covers dilution, per-oil limits and population suitability, and does not assess inhalation, aerosol droplet size, preservation or flammability.
What dilution should an essential oil blend be?
For healthy adults, roughly 1% on the face, 2% for everyday body use, and up to 3% for short-term targeted use. Children, pregnancy, and older or sensitive skin need lower levels — around 0.5% for infants and about 1% in pregnancy. These are ceilings rather than targets, so starting lower is always reasonable.
Why does my blend smell good at first and then disappear?
Because it is probably all top notes. Volatile citrus and minty oils project hard for the first twenty minutes to an hour and then evaporate; without a heart and a base there is nothing left behind. A drop or two of a fixative base — cedarwood, vetiver, patchouli or frankincense — gives the blend a tail. The analyzer shows this as a timeline so you can see where your blend runs out.
Which essential oils are unsafe around cats?
Most of them. Cats metabolise many terpene compounds far more slowly than humans, so a large share of common oils are flagged unsuitable around them — including tea tree, eucalyptus, citrus oils, peppermint and pine. Tick “cat in the home” in the analyzer and it flags every oil in your blend that carries that caution. Diffuse only briefly in a ventilated room, always let the cat leave, and ask your vet.
Is the Blend Analyzer free, and do I need an account?
It is free and needs no account. Everything is computed in your browser from Dilutio’s oil database — no AI, no uploads. It is deliberately stateless: it does not save your blends. The Dilutio app is where formulas are stored, versioned and generated.
What is a top, heart and base note?
They describe how quickly an oil evaporates. Top notes are the most volatile and lead the opening (citrus, mint). Heart notes carry the middle and give a blend its body (lavender, geranium, rose). Base notes evaporate slowest, anchor the blend and extend its wear (vetiver, cedarwood, patchouli). A blend with all three usually reads as more complete than one built from a single layer.
What this check does and doesn't cover. It compares each oil's concentration against the maximum recorded for it in our dataset, applies the ceiling for who the blend is for, and flags materials our data marks as restricted or unsuitable for that person or their pets. Coverage and provenance vary by material, and real-world limits are specific to a finished product category — so this is a formulation aid, not a compliance check. It does not assess inhalation or aerosol exposure, preservation, flammability or surface compatibility, and drop volumes are estimated at ~20 per ml (real drops vary with the oil and dropper). For professional work, weigh in grams. The analyzer is a formulation aid, not a certification: it reports your blend against published dermal maxima and dataset safety flags, and it is for education only — not medical or veterinary advice. Always patch-test, and consult a qualified professional for use during pregnancy, on children, around pets, or with a health condition. How these figures are sourced is set out in our safety-data methodology. Further reading: Tisserand Institute safety guidelines.