Castor wax, or hydrogenated castor oil, and what it does to an oil phase
Castor wax explained: 83 to 88 C melting point, hydroxyl value 150 to 165, iodine value under 5, and why 1 to 5 percent stops sweating without hardening a balm.
Castor wax is the one structurant in common balm use that does its main job below 5 percent. It is not there to harden a product, and if you dose it the way you dose beeswax you will get something brittle and chalky that nobody wants to touch. It is there to hold liquid oil inside the crystal network so the oil does not migrate out and stand on the surface, and it is unusually good at that because of a hydroxyl group that survives the hydrogenation.
Castor wax is INCI Hydrogenated Castor Oil: castor oil hydrogenated to exhaustion, melting 83 to 88 C, hydroxyl value 150 to 165, iodine value not more than 5. Use 1 to 5 percent by weight as an anti-syneresis agent, 2 percent being the usual first trial. The melt has to reach about 90 C or the wax seeds the batch.
What hydrogenation does to castor oil
Castor oil is 85 to 90 percent ricinoleic acid, which is 12-hydroxy-9-cis-octadecenoic acid: a C18 chain with a cis double bond at carbon 9 and a hydroxyl group hanging off carbon 12. Full hydrogenation saturates the double bond and leaves the hydroxyl alone. Ricinoleic acid becomes 12-hydroxystearic acid, and the triglyceride becomes glyceryl tri-12-hydroxystearate.
Two things change at once. The kink at carbon 9 disappears, so the chains straighten and pack into a crystal instead of staying liquid at room temperature. And the hydroxyl groups, now sitting on straight chains that can approach each other closely, hydrogen bond between neighbouring molecules. That second effect is what makes the material odd. Tristearin, the same triglyceride with plain C18 chains and no hydroxyls, melts at about 73 C in its stable beta form. Adding one hydroxyl per chain is worth roughly another 10 to 15 C, and it also raises the affinity of the crystal surface for polar molecules, which is why the network grips oil rather than merely occupying space in it.
Compare the other fully hydrogenated vegetable fats a maker meets. Hydrogenated soybean oil melts at 45 to 57 C and behaves like a soft, waxy butter; castor wax melts 30 to 40 degrees higher from a chain of the same length. The hydroxyl is the whole explanation, and the general argument about how crystals hold liquid is in oleogels and wax networks.
The specification, and how to read a supplier sheet
Hydrogenated castor oil has pharmacopoeial monographs, unusual for a balm wax, which makes it one of the easier materials to specify. Ask for a certificate of analysis against those values, not a marketing sheet.
| Value | Figure | What it tells you |
|---|---|---|
| Melting point | 83-88 C | 181-190 F. Far above any other fat in a balm, which is why the melt handling matters |
| Drop point (supplier method) | 85-88 C | A different measurement of the same wax, not a different wax |
| Hydroxyl value | 150-165 | The count of free hydroxyl groups. This is the number that makes it an anti-syneresis agent |
| Iodine value | not more than 5 | Proof of full hydrogenation. A higher figure means unsaturation left behind, so a softer wax with a shorter life |
| Acid value | not more than 4 | Free fatty acid from hydrolysis. High values point at poor storage or a tired lot |
| Saponification value | 176-182 | Confirms it is a triglyceride and not the free acid |
| 12-hydroxystearic acid content | about 85-90% | The rest is stearic, palmitic and traces. Tracks the fatty acid profile of the parent oil |
| Needle penetration | 2-6 dmm | Hard and brittle as a neat solid, comparable to candelilla |
| Solubility in liquid oil at 20 C | negligible | It stays a dispersed solid at use temperature. That is the point of it |
The iodine value is the specification to police. Partially hydrogenated grades exist and are cheaper, and they will not do the job: leftover unsaturation lowers the melting point, coarsens the crystal and gives you an oxidisable fraction where you wanted an inert one. A sheet that omits iodine value entirely is a sheet to query, and the general approach to supplier documents is set out in sourcing ingredients.
Why it thickens without adding much measured hardness
Neat castor wax is hard, with a needle penetration of 2 to 6 tenths of a millimetre, in the same bracket as candelilla. That number describes a block of the pure wax and is a poor guide to what 2 percent of it does inside a balm. Hardness and thickening are different properties measured by different instruments, and castor wax separates them further than any other wax on the bench.
Put 3 points of carnauba wax into a soft tin balm and the finished product gets measurably harder: a penetrometer reads lower, the surface resists a fingernail, and the balm starts to feel short and brittle when you dig into it. Carnauba crystallises into large, well-ordered platelets that add bulk stiffness, and those platelets contract as they set. Put 3 points of castor wax into the same base and the penetrometer barely moves, but the balm stops slumping under its own weight, holds a peak when you drag a spatula through it, and stops weeping. That is a rise in yield stress at almost constant hardness, and it is what rheology and yield stress exists to describe.
The mechanism is crystal size and crystal surface. Castor wax comes out of solution as very small crystallites with a large surface area per gram, and those surfaces carry hydroxyl groups that interact with the polar ends of the surrounding triglycerides. Oil is immobilised at the interface as well as trapped in pores, so a small solid fraction goes a long way. A carnauba network is coarser: more stiffness per gram, less oil held per gram. If you want the hardness measurement rather than the oil binding, castor wax is the wrong lever, and measuring balm hardness explains why the two readings diverge.
The 1 to 5 percent job: stopping a balm from sweating
Sweating is syneresis: the liquid oil exceeds what the solid network can hold, and the excess appears as beads on the surface, a slick under the lid, or free oil in the shipping box. The instinct is to add more of the wax already in the formula, which works but costs texture, since reaching a useful oil binding capacity with beeswax alone means going several points up and hardening the balm as a side effect. Castor wax buys the same binding for a fraction of that change. The full diagnosis is in balm sweating.
| Dose | % | Per 30 g tin | Per 60 g jar | Per 500 g batch | What it does |
|---|---|---|---|---|---|
| Trial | 1.0 | 0.30 g | 0.60 g | 5.0 g | Detectable reduction in beading. Try this first in a lip product |
| Standard | 2.0 | 0.60 g | 1.20 g | 10.0 g | The usual working level. Stops mild sweating in a soft tin balm |
| Firm | 3.0 | 0.90 g | 1.80 g | 15.0 g | Holds a heavy liquid oil load, suspends pigment and powders |
| Ceiling | 5.0 | 1.50 g | 3.00 g | 25.0 g | Noticeably drier and shorter on the skin. Rarely worth going here |
Worked example. A 500 g body balm batch at 10 percent beeswax, 25 percent shea butter and 65 percent liquid oils is beading in a warm room. Hold the batch size and swap 2 points of liquid oil for castor wax: remove 10 g of oil and weigh in 10 g of castor wax. The batch becomes 50 g beeswax (10 percent), 125 g shea (25 percent), 10 g castor wax (2 percent) and 315 g oils (63 percent), still 500 g and still totalling 100 percent. Nothing else changes, and the hardness reading will land within a few percent of where it was. If you would rather add without removing, x grams of wax added to 500 g gives x divided by (500 plus x), so 10.2 g lands on 2.0 percent in a 510.2 g batch. The same swap in a finished formula context is shown in body balm, and the wax substitution calculator does the arithmetic if you are trading it against another wax.
Test at 1 percent before you test at 3. Castor wax works at doses low enough that people routinely overshoot, then blame the wax for a dry, draggy afterfeel that they created themselves. Make three 50 g trial pots at 1, 2 and 3 percent, hold them at 30 C for 48 hours, and compare beading and feel together rather than one at a time.
Melt handling: the 90 C rule and what a seeded batch looks like
The melting point is 83 to 88 C, and that is the temperature at which a pure crystal collapses, not the temperature at which it disperses into a pot of oil in a reasonable time. Bring the oil phase to 90 to 95 C with the castor wax in it, hold it there, and stir until the melt is genuinely clear against a stainless spoon dipped and lifted. Then cool to your pour temperature. Adding castor wax to a batch that is already at 70 C, which is the habit people bring from beeswax, does not work: the particles soften, clump and stay.
An undissolved batch is easy to recognise once you have seen one. The melt stays faintly hazy rather than clear. The set balm shows fine white specks, most visible against a tint or on a dark surface, and it feels sandy on the lip or under a fingertip. The top surface may set matte and slightly patchy. It happens even when your thermometer says 85 C, which is exactly why the working rule is 90 C plus a clear-melt check rather than a number alone. The set faults are in undissolved wax specks and gritty balm from hard wax.
Do not take the whole batch to 90 C if it contains fragile oils, tocopherols, flavour or any heat sensitive active. Melt the castor wax in a small portion of a stable carrier, such as jojoba or high oleic sunflower, at 90 to 95 C in a separate vessel, then stir that concentrate into the main phase at 70 C. The wax stays dissolved as the blend cools through its melting range, and the rest of the formula never sees 90 C. The vessel choice and heat routes are in melting methods.
Once it is in, castor wax crystallises early on the way down, well before the beeswax or the butters, so it seeds the network rather than joining it late. That is helpful: it gives the later crystals something to grow on and produces a finer, more uniform structure. It also means a slow cool wastes the effect, because a leisurely descent through the 85 to 60 C range grows fewer, larger crystals. Pour into the container promptly and let it set at room temperature rather than in a warm oven. The temperature windows for each product type are in pour temperatures.
Grades, MP70 and MP80, and the forms it is sold in
The default material is fully hydrogenated castor oil to the pharmacopoeial specification above. The commercial grades labelled MP70 and MP80 are a different proposition: the number is a nominal melting point in degrees Celsius, and the material has been modified, usually by partial esterification or by blending, to melt lower and set less brittle. They are formulated for film flexibility and for products that cannot tolerate a 90 C melt, and they do not carry the pharmacopoeial monograph values. Treat the name as a supplier designation, not a specification, and ask for the certificate before you assume the melting point in the name is the number you will get.
Form matters more than most people expect. Micronised powder disperses fastest, because the particle is already small and the surface area high, and it is what most cosmetic suppliers sell. Flake and pastille forms weigh cleanly and do not fly, but they need longer at temperature and more stirring. For batches under a kilogram that difference is a few minutes either way, so choose on handling. Store either dry and sealed: castor wax does not go rancid in any practical sense, since an iodine value below 5 leaves almost nothing to oxidise, but powder cakes if it takes up moisture, and a caked lot weighs badly and disperses worse.
Weighing it: the dust, and what it is not
Micronised castor wax is a light, static prone powder that lifts on the smallest draught, coats the balance pan and the bench, and hangs in the air long enough to breathe. Weigh it in a still corner with the extractor off, use a deep vessel rather than a flat weighing boat, wear a dust mask, and wipe up with a damp cloth rather than brushing. It is a nuisance dust rather than a toxic one, but no fine organic powder belongs in your lungs.
One anxiety worth settling. Ricin, the toxin associated with the castor plant, is a protein that stays in the pressed seed meal. It is not present in the refined oil, and not in the wax made by hydrogenating that oil. The same applies to CB-1A, the castor bean allergen. Neither is a reason to avoid castor wax.
On cost, castor wax sits at the cheap end of the hard wax bracket, below candelilla, carnauba, sunflower and rice bran per kilogram at hobby quantities, and roughly level with bulk refined beeswax. Because the dose is 1 to 5 percent rather than the 8 to 20 percent a primary wax needs, its contribution to unit cost disappears inside rounding.
What castor wax is not
It is not castor oil, and the property most people buy castor oil for is destroyed by making it. Hydrogenation removes the double bond that keeps the molecule liquid, so the viscous, adhesive, high gloss film disappears. Castor wax adds no shine, no cling and no pigment wetting. If you want gloss you want the liquid oil, and the percentages and the tack ceiling are in castor oil. Plenty of lip formulas use both, at opposite ends of the same recipe: the oil for shine, the wax to stop the shine leaking out onto the lid.
It is also not any of the ethoxylates. PEG-40 hydrogenated castor oil, PEG-60 hydrogenated castor oil and their relatives are made by reacting the hydroxyl groups with ethylene oxide, which turns a hard hydrophobic wax into a water dispersible paste that acts as a solubiliser and a rinse-off aid. They appear in cleansing balms and in fragrance solubilisation, they contribute nothing to structure, and they will not stop a balm sweating. The names sit close enough together on an ingredient list to be confused regularly: if there is a PEG number in front, it is a surfactant, not a wax.
The two materials that do the same job differently
Castor wax is not the only way to raise oil binding without raising hardness. The two realistic alternatives work by different physics and fail in different ways.
| Material | Typical use | How it holds oil | What it costs you |
|---|---|---|---|
| Castor wax (Hydrogenated Castor Oil) | 1-5% | Fine triglyceride crystals with hydroxylated surfaces, hydrogen bonded to each other and to the oil | A 90 C melt step. Slightly drier, shorter afterfeel above 3% |
| 12-hydroxystearic acid (Hydroxystearic Acid) | 0.5-3% | Self assembled fibrillar network. The classic low molecular weight organogelator, effective at lower loadings than any wax | It is a free fatty acid. It will react with zinc oxide, some mineral pigments and alkaline actives to form soaps, and it needs a similar melt temperature |
| Fumed silica (Silica) | 0.5-3% | Hydrogen bonded particle network, thixotropic, built by shear rather than by heat | Dry, matte, draggy skin feel. A genuine respirable dust hazard when weighing. Can feel gritty if not sheared in properly |
In practice: castor wax when the balm is being poured hot anyway, because the 90 C step then costs nothing. 12-hydroxystearic acid when you need gelling at the lowest solid load and there is nothing basic in the formula for it to react with. Fumed silica when you cannot apply heat, want a matte finish, or are also fighting pigment settling, with the feel penalties in starches and silica. If the formula is simply short of structure, the answer is a primary wax, chosen from waxes compared.
Where castor wax is the wrong choice
It will not save a balm from heat. Two percent of an 85 C wax raises the softening behaviour of a finished balm by very little, because the network is still governed by the 8 to 15 percent of beeswax or plant wax doing the structural work. A balm that collapses in a hot car needs a reformulation of its primary wax, not an anti-syneresis additive, and balm melting in the heat sets out what actually moves that number.
It is a poor primary structurant. Above about 5 percent the afterfeel goes dry and short, the balm loses the cushioned drag that makes beeswax pleasant, and the surface can set with a faint bloom. Above 8 percent you have a hard, crumbly stick that snaps rather than bends. Anyone reaching for it as a vegan beeswax replacement at 10 percent has misread what it is for, and the honest options are in vegan beeswax substitutes. It is also a poor choice in any formula you cannot take to 90 C: if the pre-melt concentrate above is impractical, fumed silica does the job cold.
The decision rule is short. If a balm sweats and you like everything else about it, add 2 percent castor wax in place of 2 percent of the liquid oil and change nothing else. If a balm is too soft, castor wax is not your material. If it is both, fix the softness with the primary wax first, then look again, because raising the wax often removes the sweating on its own.
Frequently asked questions
What is castor wax and what is it made from?
Castor wax is castor oil that has been hydrogenated to exhaustion, INCI Hydrogenated Castor Oil. The process saturates the double bond of ricinoleic acid to give 12-hydroxystearic acid, so the liquid oil becomes a hard white solid melting at 83 to 88 C. It is vegan, has no odour and no colour, and contains no ricin, which stays in the seed meal.
How much castor wax should I use in a balm?
One to 5 percent by weight of the finished formula, with 2 percent the usual first working level. On a 30 g tin that is 0.6 g. Above 5 percent the afterfeel turns dry and short, and above roughly 8 percent the product becomes hard and crumbly. It is a secondary structurant, not a replacement for a primary wax.
Why does my balm have white specks after adding castor wax?
The melt did not get hot enough or was not held long enough. Castor wax melts at 83 to 88 C but needs the oil phase held around 90 to 95 C, with stirring, until the melt runs clear off a lifted spoon. Anything less leaves crystal seeds that survive into the set balm as fine white specks and a sandy feel.
Does castor wax stop a balm sweating?
Yes, that is its main use. Sweating means the liquid oil exceeds what the solid network can hold. Castor wax crystallises as very small particles with hydroxylated surfaces that both trap and bind oil, so 1 to 3 percent raises oil binding capacity substantially while barely changing measured hardness. Swap it in for an equal weight of liquid oil.
Is castor wax the same as PEG-40 hydrogenated castor oil?
No. PEG-40 and PEG-60 hydrogenated castor oil are ethoxylated derivatives, made by reacting the hydroxyl groups with ethylene oxide. They are water dispersible solubilisers and rinse-off aids used in cleansing balms, they are pastes rather than hard waxes, and they add no structure at all. The names look similar on an ingredient list and are frequently confused.
Will castor wax make my balm harder?
Barely, at the doses it is used at. It raises yield stress, so the balm holds its shape and stops slumping and weeping, but a penetrometer reading changes very little at 2 or 3 percent. If you want measurable hardness, carnauba or candelilla will give you more per point, along with the brittleness that comes with them.
Does castor wax go rancid?
Not in any practical sense. Its iodine value is below 5, which means there is almost no unsaturation left for oxygen to attack, so it is one of the most stable materials on a balm bench. Stored dry and sealed it keeps for years. Powder grades cake if they take up moisture, which affects weighing and dispersion rather than safety.
Sources and further reading
- European Directorate for the Quality of Medicines and HealthCare, European Pharmacopoeia monograph: Hydrogenated castor oil (Ricini oleum hydrogenatum), Strasbourg.
- United States Pharmacopeial Convention, USP-NF monograph: Hydrogenated Castor Oil, Rockville MD.
- Cosmetic Ingredient Review, Final report on the safety assessment of Ricinus communis (castor) seed oil, hydrogenated castor oil and related ingredients, International Journal of Toxicology, 2007.
- European Commission, CosIng cosmetic ingredient database, entry for Hydrogenated Castor Oil.
- Rowe, Sheskey and Quinn (eds), Handbook of Pharmaceutical Excipients, monograph on hydrogenated castor oil, Pharmaceutical Press, London.
- Marangoni and Garti (eds), Edible Oleogels: Structure and Health Implications, AOCS Press, Urbana IL (12-hydroxystearic acid and wax crystal networks).
Reviewed and updated 6 September 2026. Spotted an error? Tell us and we will fix and log it.