What will dissolve in an oil and wax balm, and what will stay gritty?

Menthol, camphor and thymol dissolve in oil. Glycerin, urea, allantoin, salt and sugar do not. Pharmacopoeia solubility for 20 balm ingredients, and the fixes.

Anything oily or waxy in character will dissolve in a balm, and anything that dissolves in water will not. The United States Pharmacopeia calls menthol and camphor freely soluble in fixed oils, which means a gram dissolves in 1 to 10 mL of oil, and it lists thymol at one gram in 2 mL of olive oil. It calls glycerin insoluble in fixed and volatile oils, and urea, allantoin, panthenol, salt and sugar have no oil anywhere in their lists of solvents. Between the two groups sit a few materials that dissolve only up to a ceiling, and those cause most of the grit people find in a tin days after pouring. The rule underneath all of it is polarity.

• Menthol, camphor: freely soluble in oils
• Thymol: 1 g in 2 mL olive oil
• Glycerin: insoluble in oils
• Allantoin: 0.57% in water, none in oil
• Menthol and camphor liquefy together

Like dissolves like, and what "polar" means in a balm

Water molecules hold each other by hydrogen bonds, so what dissolves in water is what can join in: ions such as sodium and chloride, and molecules carrying several hydroxyl, amide or acid groups, such as sugar, glycerin, urea and allantoin. Oils hold each other only by the weak attraction between long hydrocarbon chains. A material dissolves in oil if it is mostly hydrocarbon itself, with at most one or two polar groups that the rest of the molecule can carry. Menthol is a ten carbon ring with a single hydroxyl. Sucrose is twelve carbons carrying eight hydroxyls. One disappears into a warm oil; the other sits in it as sand.

Polarity is not a yes or no property, which is why the useful picture is a ladder. At the bottom are hydrocarbons such as mineral oil and petrolatum, and squalane, with no polar groups at all. Above them come the triglyceride oils and butters, where three ester groups sit in a large molecule that is otherwise all chain. Then the shorter esters, then castor oil, whose ricinoleic acid carries a hydroxyl on every chain. Above the oils come the glycols, then glycerin, then water. Two liquids far apart on the ladder do not mix, and a solid dissolves best in the liquid nearest to it.

The pharmacopoeia records the ladder in its own words. Mineral oil is "miscible with most fixed oils but not with castor oil". Castor oil, unusually for an oil, is "miscible with dehydrated alcohol". Isopropyl myristate is miscible with fixed oils but "insoluble in water, in glycerin, and in propylene glycol". Propylene glycol "will dissolve many essential oils, but is immiscible with fixed oils", and glycerin is "insoluble in chloroform, in ether, and in fixed and volatile oils". Read in that order, those entries are the ladder from the bottom rung to the top.

Reading a solubility statement as a number

Most of the solubility data a maker can find are not numbers but words: soluble, sparingly soluble, practically insoluble. They are numbers in disguise. The United States Pharmacopeia defines each term by how many parts of solvent dissolve one part of the solid. Converted to grams of solid per 100 mL of solvent, the scale becomes something you can set against a formula percentage.

Two cautions come with the scale. First, the definitions are for room temperature, and the pharmacopoeia describes the statements as "general in nature", so treat a term as a band, not a measurement. Second, a term only applies to the solvent it names. "Soluble in alcohol" says nothing about jojoba, and many entries never mention an oil at all, because the reference books were written for pharmacists working with water, alcohol, ether and chloroform.

Twenty balm ingredients, sorted by whether oil can dissolve them

The table gathers the reference entries for the materials makers actually try to put into balms. The oil column quotes the pharmacopoeia where it names an oil, and the Merck Index or CRC Handbook figures held in PubChem where it does not. Water figures are included because they show which side of the ladder each material belongs to.

Sucrose is "practically insoluble in dehydrated alcohol", which is far more polar than any oil, so no oil on the bench will take sugar up. That is what a lip scrub relies on. Potassium sorbate needs over a litre of ether per gram, which is why a water soluble preservative stirred into a balm protects nothing.

The monograph ranges in the last column make the problem concrete. The US skin protectant monograph lists glycerin at 20 to 45 percent and allantoin at 0.5 to 2 percent. Glycerin at 20 percent in an oil base is not a balm, it is a separating mixture. Allantoin's minimum dose is close to its whole solubility in water, 0.57 percent, and far above anything an oil can hold. The allantoin page works through what that means for a lip balm claim, and the same reasoning sinks urea in an anhydrous foot balm.

What happens to a solid that does not dissolve

An undissolved solid in a balm is a dispersion: separate particles sitting in a continuous oil phase. In the melt nothing holds them up, so dense crystals sink while the batch is liquid. Once the wax sets, the particles are held only by the crystal network. A balm is an oleogel, a liquid oil held still by a few percent of wax crystals, as set out in how much wax gels an oil, and that scaffold can trap a particle but cannot dissolve it.

Three faults follow from a dispersion that was meant to be a solution. The first is grit. The second is uneven dosing: with an active half dissolved and half settled, the first tin poured is weak and the last is strong. The third is that nothing happens on the skin. Allantoin, urea and panthenol act in water. A crystal in a film of oil has nothing to dissolve in, so the label promises an active the product cannot deliver in that form.

A dispersion is not always a fault. Zinc oxide, iron oxides, micas and scrub sugar are meant to stay solid. The difference is that a deliberate dispersion is designed: the powder is wetted before it meets the wax and the network is strong enough to hold it.

Liquids that will not mix: glycerin, glycols and "extracts"

Liquids follow the same rule, and the fault is easier to miss because a liquid stirred into a hot melt can look mixed. Glycerin, propylene glycol, aloe juice, hydrosols, glycerites and glycol based extracts all sit high on the ladder and break into droplets in a melt. In the tin the droplets coalesce, sink or bead on the surface, giving sticky patches or a syrupy layer at the bottom. The glycerin page describes every glycerin balm as a suspension held up by the wax network's yield stress, and that is the best case.

Propylene glycol confuses people. The pharmacopoeia says it "will dissolve many essential oils", so a scent diluted in a glycol seems compatible with an oily product, but the same entry says it "is immiscible with fixed oils". The essential oil is happy in either liquid; the glycol carrying it is not happy in the balm. That is why the diluent matters as much as the scent, as fragrance oils in balms explains.

Water is the extreme case, and adding any changes the product category, as anhydrous formulation explains. The magnesium balm formula shows both routes for an ingredient that will not go into oil: a proper water-in-oil emulsion, or a dry dispersion that accepts the limits.

What dissolves, and the ceiling that still applies

Small, mostly hydrocarbon molecules dissolve well: menthol, camphor, thymol, tocopherol and most fragrance materials. Menthol is freely soluble in mineral oil and fixed oils, which on the scale above means somewhere between 10 and 100 g per 100 mL. The doses on this site run from about 1 percent in a foot balm to under 3 percent in a chest rub, as the menthol and camphor page sets out, so they sit far below the limit. Thymol is quantified: one gram in 2 mL of olive oil, roughly 50 g per 100 mL.

Not every oil soluble material is soluble without limit, and the pharmacopoeia's figures show how quickly a ceiling arrives. Benzocaine dissolves at one gram in 30 to 50 mL of almond or olive oil, which is about 2 to 3.3 g per 100 mL. Precipitated sulfur dissolves at one gram in 100 mL of olive oil, about 1 g per 100 mL, while the US acne monograph range for sulfur is 3 to 10 percent. At any dose in that range, most of the sulfur in an oil base is suspended powder, not solution. These are drug ingredients, quoted for the shape of the problem: a measurable ceiling, close to or below the dose people want.

Saturation, temperature and crystals that appear later

Solubility rises with temperature for nearly every solid, so a hot melt holds more of a crystalline active than the same oil at 20 C. Something that "dissolved perfectly" can turn up as needles or a fine bloom days later: the solution was supersaturated as it cooled, and given time and a crystal of wax to grow on, the excess comes out.

Ascorbyl palmitate is the clean example. The pharmacopoeia calls it very slightly soluble in vegetable oils, which puts its room temperature limit at about 0.01 to 0.1 g per 100 mL. This site's vitamin C page notes that warm oil takes up around a percent, and that much of it recrystallises. Both statements are true, and the gap between them is the problem: a dose that dissolves at the pouring temperature is ten times what the oil can keep in solution once it is cold. The same mechanism lies behind delayed grit from salicylic acid, and from menthol in a balm overdosed for a strong cooling effect. It looks like the grain in shea butter, which comes from fat crystals changing form, but the cause is different. If specks appear, undissolved wax specks covers how to tell a wax that never melted from a solid that came back out.

Salicylic acid: the active that causes the most trouble

Salicylic acid is the ingredient people most often expect to dissolve in a balm. It dissolves at one gram in 3 mL of alcohol or ether, according to the pharmacopoeia's table, but in the less polar solvents the tables list, it collapses. One gram needs 135 mL of benzene, about 0.74 g per 100 mL, and the Merck figure reproduced in PubChem is 0.262 percent by weight in carbon tetrachloride at 25 C. Neither reference gives any figure for a fixed oil, a cosmetic ester or mineral oil. A 2003 US patent on salicylic acid solvents states the practical result: salicylic acid "is not sufficiently soluble in water or oils traditionally used in the cosmetic and dermatological preparations", and it "tends to crystalize out of the various compositions".

The US acne monograph allows salicylic acid at 0.5 to 2 percent. The patent's answer was a 30 percent solution in butylene glycol and glycereth-26, glycols high on the ladder and no more compatible with an oil and wax base than propylene glycol. Within a balm, the only lever is a more polar oil phase: polar esters and castor oil rather than squalane, mineral oil or a light triglyceride. The cosmetic esters page names the more polar ones.

With no reference figure for any balm oil, the dose has to be checked in the actual blend, at room temperature, over weeks. A solution that is clear when hot proves nothing.

Eutectics: why menthol and camphor turn liquid together

Two crystalline solids mixed together can melt below either one alone; the lowest melting mixture is the eutectic. L-menthol melts at 41 to 43 C according to the Merck Index, and camphor at 174 to 179 C according to Hawley's Condensed Chemical Dictionary. Phaechamud and colleagues, in a 2016 study in AAPS PharmSciTech, mapped the pair by differential scanning calorimetry and found that "a eutectic point of this system was near to 1:1 menthol/camphor and its eutectic temperature was -1°C". A half and half mix of the two solids is a liquid at room temperature.

The same study measured how fast each part leaves. Menthol showed a lower apparent sublimation rate than camphor, and the eutectic liquid evaporated more slowly than camphor sublimed but faster than menthol evaporated. For a maker that means a convenient way to add both actives, by letting the weighed crystals liquefy together in a small jar and pouring the liquid into the warm oil, and a reason to do it immediately before use and off the heat, not on an open bench while the wax melts.

Wetting a powder that is meant to stay solid

For the materials that should never dissolve, the job is the opposite of dissolving: the powder must be dispersed as single, separate particles. A dry pigment or mineral powder arrives as clumps of particles stuck together with air between them. Dropped into a melt, the oil coats the outside of each clump and the inside stays dry, so the clumps survive as specks of colour or white streaks. Even zinc oxide gives a streaky balm if the clumps are never broken down.

The remedy is to wet the powder in a small amount of liquid oil before it meets the main batch: work it into a paste, grind or mull it until the paste is smooth, then stir the paste into the melt. Castor oil is the usual choice on this site, the method used for colourants and tints.

Check the figure before you design an active in

Look up solubility before choosing a dose, not after a batch has failed. It takes five steps.

1. Find a figure in a named solvent and temperature. A supplier data sheet that gives percent at 25 C in a named oil or ester is the best source. Failing that, convert the pharmacopoeia term with the table above.
2. Check the solvent matches your oil phase. A figure in ethanol, propylene glycol or "organic solvents" tells you nothing about a beeswax and sunflower base. Where the reference names no oil, assume the ingredient will not dissolve in one.
3. Compare the dose with the ceiling at room temperature. Work out the active as grams per 100 g of the liquid oil fraction, not of the whole balm, since wax and butter are not solvents once solid. Leave a clear margin below the limit, because a cold winter shelf is below the reference temperature.
4. Dissolve it properly. Add the active to a warm portion of the liquid oil, off the heat, and stir until it is completely clear before the wax goes in.
5. Test for delayed crystals. Pour a small test tin, keep it at room temperature and a second in a cool place, and smear a little of each on dark glass at 1, 7 and 28 days. A sharp edge or a sparkle under a hand lens means the active is coming out of solution.

Where these figures stop applying

The reference data here are approximate, describe room temperature, and almost never name the oils balm makers use. Of the twenty ingredients in the main table, only thymol, benzocaine and sulfur have a number for a named oil, a few more have a descriptive term for "fixed oils" or "vegetable oils", and none has an entry for jojoba, squalane, shea or a cosmetic ester. A figure in olive oil says most about other liquid triglycerides and least about mineral oil or castor oil, which sit at opposite ends of the ladder.

The figures are also for a single solid in a single liquid. No source cited here measured solubility in a finished balm, or how quickly a supersaturated balm recrystallises. Dissolving an ingredient is not the same as making it work, and claims about effects on skin can turn a cosmetic into a drug, as covered in cosmetic vs drug claims.

What the data do settle is the direction. If a material's reference entry names an oil it dissolves in, it belongs in a balm and the question is only how much. If it names water, glycerin or alcohol and no oil, the honest options are a designed dispersion, an emulsion, or leaving it out. For lips specifically, ingredients for chapped lips sorts the materials that work in a balm from the ones that only look good on the label.

Reviewed and updated 18 October 2026. Spotted an error? Tell us and we will fix and log it.