Why the name of an oil tells you less than you think
Ask a formulator why a balm went grainy, why a facial oil turned rancid before its shelf life ran out, or why a cream that worked beautifully with sunflower oil fell apart when the supplier swapped in "high-oleic sunflower", and the answer is almost never in the name on the drum. It is in the fatty acids. An oil is a mixture of triglycerides, and each triglyceride carries three fatty-acid chains. The length of those chains and the number of double bonds in them decide whether the oil is solid or liquid on a British windowsill, how fast it oxidises, how it feels on skin, and how much of it your safety assessor will let you put in a leave-on product before asking for stability data.
This article is the map for a series. Instead of walking through oils one by one, it sorts them into ten fatty-acid groups and shows what each group predicts. Once you know the group, you can reason about an oil you have never handled, read a supplier's certificate of analysis with confidence, and stop treating every new botanical as a mystery. Each group gets its own deep-dive later in the series; here you get the framework and the routing table.
How to read a fatty-acid profile in two minutes
A full certificate of analysis (CoA) for a plant oil includes a table of fatty acids expressed as a percentage of the total, normally determined by gas chromatography. The shorthand is simple once decoded. C18:1 means a chain of 18 carbon atoms with one double bond (oleic acid). C18:2 has two (linoleic), C18:3 three (alpha-linolenic or gamma-linolenic, depending on where the bonds sit). C12:0 is a 12-carbon chain with no double bonds (lauric acid). C22:1 is a 22-carbon chain with one bond (erucic acid).
Three things follow from those two numbers, and they drive almost everything in the rest of this article:
- Chain length sets melting behaviour. Longer saturated chains pack tightly and melt higher: that is why palm oil and the butters are solid and why short-chain lauric oils sit on the boundary between solid and liquid at room temperature.
- Double bonds lower the melting point and raise the oxidation risk. A cis double bond is a kink that stops chains packing, so unsaturated oils stay liquid. Oxidation starts at the carbons next to a double bond, and a carbon sitting between two double bonds is the weakest point of all, which is why one bond (oleic) is comparatively robust, two (linoleic) oxidise noticeably faster and three (linolenic) faster still.
- The unsaponifiable fraction is the part that does not turn into soap under the test conditions. It holds the tocopherols, sterols, squalene and triterpenes. It is a small share of the oil by mass, yet it carries a surprising part of the oil's stability and character. Codex caps it for each named oil, from 15 g/kg for coconut to 65 g/kg for rice bran, and unrefined oils sit higher than refined ones.
The Codex Alimentarius standard for named vegetable oils (CXS 210-1999) publishes authentic-sample composition ranges for the major edible oils, and it is the single most useful reference for a formulator who wants a neutral baseline to compare a supplier's numbers against. Most of the ranges below come from it; the rest are from peer-reviewed compositional studies, cited at the end.
The ten groups at a glance
| Group (dominant acid) | Typical oils and reference ranges | What it predicts in a formula |
|---|---|---|
| 1. Lauric (C12:0) | Coconut 45.1–53.2 % C12:0; babassu 40.0–55.0 %; palm kernel 45.0–55.0 % (Codex CXS 210) | Solid in a cool room, liquid in a warm one; in practice described as quick to absorb and, at high shares, drying; excellent lather in soap; very low iodine value (coconut 6.3–10.6), so oxidatively stable. |
| 2. Oleic (C18:1) | Olive 55.0–83.0 % C18:1 (Codex CXS 33); high-oleic sunflower 75.0–90.7 %; high-oleic safflower 70.0–83.7 %; argan 39.5–50.8 % oleic with 27.1–39.3 % linoleic | The predictable base: stable for a liquid oil and, in most formulators' experience, rich rather than light. Too much of it reads as heavy on oily skin. |
| 3. Linoleic (C18:2) | Sunflower 48.3–74.0 %; grapeseed 58.0–78.0 %; safflower 67.8–83.2 %; soybean 48.0–59.0 %; maize 34.0–65.6 % | Typically described as light and fast-absorbing; pays for it with a higher iodine value (sunflower 118–141, grapeseed 128–150) and a shorter shelf life. Needs an antioxidant plan. |
| 4. Gamma-linolenic (C18:3 n-6) | Borage about 21 % GLA; blackcurrant seed about 17 %; evening primrose about 9 % (14 of 16 commercial brands tested contained 7–10 %) | Specialist oils bought for their GLA content and positioned for dry, sensitive skin; expensive; used at low percentages and added at the cool-down stage. |
| 5. Alpha-linolenic, omega-3 (C18:3 n-3) | Rosehip seed oil 45–51 % alpha-linolenic in a Bulgarian sample set; low-erucic rapeseed 5.0–14.0 %; soybean 4.5–11.0 % | The least stable working group. Three double bonds oxidise fastest; storage and packaging decide whether the benefit survives to the skin. |
| 6. Palmitic and stearic (C16:0, C18:0) | Palm oil 39.3–47.5 % C16:0; shea butter dominated by stearic in West Africa and by oleic in Uganda; cocoa butter built on palmitic, stearic and oleic | Solid butters and structuring fats. Hardness and melting range come from here; so does the crystallisation trouble covered in our butter polymorphism article. |
| 7. Ricinoleic (hydroxy C18:1) | Castor oil, the only common oil dominated by a hydroxy fatty acid | Viscous, tacky, soluble in ethanol, gloss-forming. Irreplaceable in lip products and clear systems; out of place where a light feel is wanted. |
| 8. Wax esters | Jojoba: about 98 % wax esters rather than triglycerides | Not a triglyceride oil. Known for its stability and silky feel; it should not be compared with triglyceride oils on the same footing. |
| 9. Very-long-chain, erucic (C22:1) | High-erucic rapeseed above 2.0 up to 60.0 % C22:1; mustard seed 22.0–50.0 %; low-erucic rapeseed not more than 2.0 % | A boundary group. Modern culinary rapeseed was bred low-erucic; old data about "rapeseed oil" often describe a different material. Read the variety on the CoA. |
| 10. Conjugated (C18:3 with conjugated bonds) | Pomegranate seed oil more than 70 % punicic acid | Rare chemistry and strong claims. Used as a small-percentage active, not a base. |
Two things stand out from the table. First, the same botanical can sit in two groups: ordinary sunflower is a linoleic oil, high-oleic sunflower is an oleic oil, and Codex lists them as separate named products with separate ranges. If a supplier substitutes one for the other, your formula's feel, shelf life and even emulsion stability can change while the label stays the same. Second, the ranges are wide. Olive oil legitimately runs from 55 to 83 percent oleic acid. Shea butter from Uganda is a different fat from shea butter from Mali. That variability is not a defect in the standard; it is why the CoA of the batch you actually bought matters more than any published average, a point developed in our article on how climate changes oil composition.
What each group does on skin and in the pot
Lauric oils: the boundary between solid and liquid
Coconut, babassu and palm kernel are unusual in being dominated by a 12-carbon saturated acid, with meaningful shares of C8, C10 and C14 alongside it (coconut carries 4.6–10.0 % C8:0, 5.0–8.0 % C10:0 and 16.8–21.0 % C14:0 on Codex ranges). Short saturated chains melt low for saturated fats and pack tightly enough to be solid in a cool room, which is why a jar of coconut oil is a white block in January and a clear liquid in a heatwave. The soaps made from them are famously foamy and, at high shares, famously stripping. The comedogenicity reputation deserves care: the human patch work by Draelos and DiNardo (2006), a six-subject modified Mills and Kligman assay, found that finished products containing ingredients from the comedogenic lists were not necessarily comedogenic, which is a good reason to test the product rather than condemn the ingredient. Fractionated coconut oil (caprylic/capric triglyceride) is a different material again, stripped of the C12 that defines the group.
Oleic oils: the base you build on
One double bond is the sweet spot between liquidity and stability. Olive, high-oleic sunflower, high-oleic safflower, argan and their relatives are the oils a formulator reaches for when the job is to carry actives, give a cushion of slip and last a full shelf life without drama. The cost, in most formulators' experience, is richness: oleic oils are felt as fuller and slower than linoleic ones, which is welcome on dry, mature skin and unwelcome in a mattifying gel-cream. Argan is worth a note because it sits on the border of two groups, roughly half oleic and a third linoleic, which is much of the reason it feels lighter than olive.
Linoleic oils: light, barrier-relevant, impatient
Sunflower, grapeseed, safflower, soybean and maize oils are the ones formulators describe as light, and this group dominates "for oily and combination skin" marketing; whether that reputation survives scrutiny is a question for the linoleic deep-dive. The bill arrives as oxidation: two double bonds per chain give these oils iodine values well above 100, and a cold-pressed grapeseed oil that arrives at a peroxide value near the Codex ceiling of 15 milliequivalents per kilogram has already undergone measurable primary oxidation before you open the drum. If you formulate with this group, the antioxidant and packaging decisions are not optional extras.
GLA and omega-3: actives disguised as oils
Borage, evening primrose and blackcurrant seed oils are bought for one fatty acid, gamma-linolenic, and the numbers matter: roughly 21 percent in borage, 17 in blackcurrant and 9 in evening primrose, so a formula "with evening primrose oil" delivers less than half the GLA of the same percentage of borage. The omega-3 group, led by rosehip seed oil, carries alpha-linolenic acid with three double bonds and is the fastest-oxidising material most formulators will ever handle. Both groups belong at the end of the process, added at the cool-down stage and at low percentages, with the shelf life of the whole product in mind.
Butters: structure, and the crystals that come with it
Palmitic and stearic acids are what make a butter a butter. Palm oil's 39–48 percent palmitic, shea's stearic backbone, and cocoa butter's palmitic-stearic-oleic mix give hardness and a melting range that can be tuned by blending. The same saturated chains crystallise in several forms, which is where grainy body butters and blooming lip balms come from; the fix is tempering, and it has its own article in this series. Shea deserves a warning that applies to the whole group: the Di Vincenzo survey of 150 samples across four African countries found stearic acid dominant in West African shea and oleic acid dominant in Ugandan shea, with regional mean triterpene contents ranging from 3.69 to 12.57 percent. Two drums labelled "shea butter" can be two different raw materials, a problem we walk through in why your shea butter acts differently.
The outliers: castor, jojoba, erucic and conjugated oils
Castor oil is dominated by ricinoleic acid, an 18-carbon chain with a hydroxyl group on it. That single OH group raises the polarity of the molecule and lets the chains hydrogen-bond, which is the root of castor's distinctive viscosity and its behaviour in ethanol-based systems. Jojoba is not a triglyceride oil at all but a liquid wax, about 98 percent wax esters, which is why it should not be judged against tables built for triglycerides. High-erucic rapeseed and mustard oil carry 22-carbon monounsaturated chains; culinary rapeseed was bred to keep erucic acid at or below 2 percent, so the variety on the CoA decides which material you are holding. Pomegranate seed oil, with more than 70 percent punicic acid, has conjugated double bonds, a reactive chemistry that is part of why it is dosed as an active rather than used as a base.
Reading a supplier's certificate of analysis
Once the groups are clear, a CoA stops being a wall of numbers. Five lines carry most of the information.
- Fatty-acid profile. Check the dominant acid first and place the oil in its group. Then check the Codex range for the named oil. A "sunflower oil" at 80 percent oleic is a high-oleic variety, whatever the invoice says. A rapeseed oil above 2 percent erucic is not the low-erucic grade.
- Iodine value. A single number for total unsaturation and therefore for oxidation risk. Codex ranges give you the expected band: coconut 6.3–10.6, palm 50.0–55.0, high-oleic sunflower 78–90, low-erucic rapeseed 105–126, sunflower 118–141, grapeseed 128–150. If the value falls outside the band, investigate identity, method and possible adulteration before the oil goes anywhere near a batch.
- Peroxide value. A freshness measure. Codex quality factors allow up to 10 milliequivalents of active oxygen per kilogram for refined oils and 15 for cold-pressed and virgin oils (virgin olive oils, under their own standard, up to 20). A batch that arrives near the ceiling has already undergone measurable primary oxidation; the value is a snapshot at testing, not a countdown.
- Acid value. Free fatty acids, which may indicate hydrolysis or poor handling. Codex quality limits: 0.6 mg KOH per gram for refined oils, 4.0 for cold-pressed and virgin oils.
- Unsaponifiable matter. Codex maximums differ by oil (coconut not more than 15 g/kg, rapeseed and grapeseed 20, rice bran as high as 65). This is where the sterols and tocopherols live; an unusually low figure in an oil sold as unrefined is worth a question to the supplier.
For a UK brand these numbers are not academic. The safety assessor writing your Cosmetic Product Safety Report will ask how you justified the shelf life and the period-after-opening, and "the oil supplier said it was stable" is not an answer. Batch CoAs with iodine and peroxide values, a stated antioxidant and a stability rationale are the supporting evidence; the assessor will still expect stability data on the finished product itself. Keep the batch CoA with the product information file.
A decision table: start from the job, not the plant
| What the formula needs | Reach for | Watch out for |
|---|---|---|
| A stable, forgiving liquid base for a cream or facial oil | Oleic group: olive, high-oleic sunflower, argan | Heaviness on oily skin; olive's odour in fragrance-free products |
| A light, fast-absorbing feel | Linoleic group: grapeseed, sunflower, safflower | Shelf life; plan the antioxidant and the packaging before the first batch |
| Hardness in a balm, stick or body butter | Palmitic-stearic group: shea, cocoa, mango; palm-derived fractions | Polymorphism; test a tempered and an untempered sample side by side |
| Foam and cleansing in a bar soap | Lauric group: coconut, babassu, palm kernel | Stripping feel at high shares of the blend; balance with oleic oils |
| Gloss, tack and cling in lip products | Ricinoleic: castor | Tack where it is not wanted; heavy feel in face products |
| A very stable oil that still feels like an oil | Wax esters: jojoba | Price; it will not behave like a triglyceride in calculations |
| A GLA-rich positioning for dry, sensitive skin | GLA group: borage, blackcurrant, evening primrose | Cost per unit GLA; oxidation; substantiation for any claim you print |
| An omega-3 story | Rosehip, chia, sacha inchi | The fastest-oxidising group; airless packaging or an honest decision not to include it |
Two misconceptions the map clears up
"Oils are interchangeable if they are both natural." They are interchangeable only within a group, and only approximately. Swapping grapeseed for high-oleic sunflower moves the iodine value from the 128–150 band to the 78–90 band, and with it the oxidation risk and the feel on skin. Swapping ordinary sunflower for high-oleic sunflower moves the oil from group 3 to group 2 and can change an emulsion's stability. Always re-test after a substitution, and record the variety, not just the botanical name.
"This oil is comedogenic, so any product with it is." Comedogenicity ratings mostly descend from raw-material assays. When Draelos and DiNardo tested finished cosmetic products on human volunteers using a modified Mills and Kligman method, finished products using ingredients from the comedogenic lists were not necessarily comedogenic. The study was small, six subjects, but its point stands: the right unit of judgement is the finished product at its real use level, which is also what a UK claims reviewer will want to see.
Where the series goes from here
Each group above gets its own article, written the same way: composition first, behaviour second, claims last, with the primary sources listed. The lauric, oleic and linoleic groups come first because they cover most of what a formulator buys; then a practical guide to reading oxidative stability numbers and turning them into a shelf-life estimate; then the GLA and omega-3 specialists, the butters and their unsaponifiables, castor and jojoba, and the boundary cases. Two spokes already exist: polymorphism of butters and how climate changes fatty-acid composition. If you want the skin-side view of the same chemistry, start with how an oil's fatty acids determine its effect in a formula.
Keep this page open the next time a CoA lands in your inbox. The group tells you what to expect; the certificate tells you whether this batch delivers it.
Sources
- Codex Alimentarius. Standard for Named Vegetable Oils, CXS 210-1999 (amended 2015). Table 1 fatty-acid composition, Table 2 chemical and physical characteristics, Appendix quality factors. FAO PDF
- Codex Alimentarius. Standard for Olive Oils and Olive Pomace Oils, CXS 33-1981 (revised 2015). Fatty-acid composition and peroxide value tables. FAO PDF
- Bučar Miklavčič M., Taous F., Valenčič V., Elghali T., Podgornik M., Strojnik L., Ogrinc N. Fatty Acid Composition of Cosmetic Argan Oil: Provenience and Authenticity Criteria. Molecules, 2020. PMC7570657
- Di Vincenzo D., Maranz S., Serraiocco A., Vito R., Wiesman Z., Bianchi G. Regional variation in shea butter lipid and triterpene composition in four African countries. Journal of Agricultural and Food Chemistry, 53(19), 2005. PubMed 16159175
- Gad H. A. et al. Jojoba Oil: An Updated Comprehensive Review on Chemistry, Pharmaceutical Uses, and Toxicity. Polymers, 13(11), 2021. PubMed 34073772
- Sergeant S., Rahbar E., Chilton F. H. Gamma-linolenic acid, dihomo-gamma-linolenic acid, eicosanoids and inflammatory processes. European Journal of Pharmacology, 2016. PMC4975646
- Gibson R. A., Lines D. R., Neumann M. A. Gamma linolenic acid (GLA) content of encapsulated evening primrose oil products. Lipids, 27(1), 1992. PubMed 1318991
- Characterization of Bulgarian Rosehip Oil by GC-MS, UV-VIS Spectroscopy, Colorimetry, FTIR Spectroscopy, and 3D Excitation-Emission Matrix Fluorescence. Molecules, 30(19), 2025. PubMed 41097383
- Inclusion complex of fatty acids of pomegranate seed oil with beta-cyclodextrin: preparation, characterization and bioactivity. Journal of Food Science and Technology, 63(1), 2026. PubMed 41684478
- Ogunniyi D. S. Castor oil: a vital industrial raw material. Bioresource Technology, 97(9), 2006. PubMed 15919203
- Draelos Z. D., DiNardo J. C. A re-evaluation of the comedogenicity concept. Journal of the American Academy of Dermatology, 54(3), 2006. PubMed 16488305
