Allantoin: a monograph active that barely dissolves in an oil phase

Allantoin is soluble at about 0.5 percent in water and far less in oil. The US monograph range of 0.5 to 2 percent, the grit problem and how to disperse it.

Allantoin is the cheapest way to put a monograph-backed skin protectant into a balm and one of the easiest ways to end up with a gritty one. It dissolves in water at roughly half a percent and in cosmetic oils at effectively nothing, so in an anhydrous product it is a suspended powder rather than a dissolved active. This page covers the numbers that decide whether that suspension feels smooth or sandy, and what the powder actually earns you on a label.

• INCI: Allantoin
• CAS 97-59-2
• Water 0.5% at 25 C
• Oil solubility negligible
• US monograph 0.5-2%

What allantoin is

Allantoin is 5-ureidohydantoin, a small heterocyclic molecule of molecular weight 158.1, supplied as a white, odourless, tasteless crystalline powder. Biologically it is the product of uric acid oxidation. Most mammals make it and excrete it; humans and other higher primates lost the urate oxidase enzyme and excrete uric acid instead, which is why allantoin appears in veterinary and plant chemistry long before it appears in cosmetics. In plants it is a nitrogen transport compound, concentrated in comfrey root, wheat sprouts and several beans.

Every commercial cosmetic grade you can buy is synthesised, almost always by reacting urea with glyoxylic acid. The result is a single compound with a defined melting behaviour and a pharmacopoeial assay, not a botanical extract with a variable profile. That matters more than it sounds, because the whole practical story of allantoin in a balm is the story of one crystalline solid that will not dissolve in the vehicle you have put it in.

The solubility problem, stated as arithmetic

Do the sum before you buy the powder. In a fully anhydrous balm there is no water and no glycol, so the amount of allantoin that can go into solution is zero. Every gram you add stays as a solid, dispersed through the oil and wax and held in place by whatever structure the balm develops as it sets.

Adding a humectant does not rescue it. Suppose you build a balm with 5 percent glycerin, which is already at the upper end of what an anhydrous product will carry without feeling sticky. At roughly 1 g per 100 g, that 5 g of glycerin can hold about 0.05 g of allantoin, which is 0.05 percent of a 100 g batch. Dose at the monograph minimum of 0.5 percent and 90 percent of the material is still solid. The general case is set out in solubility in anhydrous formulas, and the sticky-versus-useful trade on the humectant itself is in glycerin and humectants.

So the design question is never "how do I dissolve allantoin in my balm". It is "how small are the particles, and will the base hold them still". Everything below follows from that.

What the US monograph actually permits

Allantoin appears in the US over-the-counter skin protectant monograph, 21 CFR part 347, at 0.5 to 2 percent. That is a drug listing, not a cosmetic permission. If you sell in the United States at that level and make the associated claims, the product is an OTC drug: it needs a Drug Facts panel in the format set by 21 CFR 201.66, an active ingredient statement, a purpose of "skin protectant", indications restricted to the monograph wording, and facility registration and product listing. The wording the monograph supports is narrow and unglamorous, along the lines of helping prevent and temporarily protecting chafed, chapped, cracked or windburned skin.

There is no equivalent monograph in the UK or the EU. Allantoin there is an ordinary cosmetic ingredient, and any claim you make about it has to satisfy the common criteria for cosmetic claims: substantiated, truthful, and not implying a medicinal effect. "Helps repair damaged skin" and "heals" cross that line in either jurisdiction. The full mapping of what you may and may not say is in cosmetic versus drug claims, with the paperwork side in labelling cosmetics in the US and labelling cosmetics in the EU.

Why an undissolved crystal stays a crystal

This is the point that separates allantoin from the grain most makers have already met. Grainy shea is fat crystallised into a coarse polymorph, and it melts at skin temperature, so it feels rough for a second and then vanishes. Allantoin melts at around 230 C. Nothing on a lip or a fingertip will soften it. Whatever particle size goes into the pot is exactly what the customer feels, for the life of the product. If your instinct on grit was trained by grainy shea butter, retrain it here.

Size and shape both matter. Detection thresholds for hard particles on skin are usually put somewhere around 20 to 30 micrometres, and lower on the lip, where mechanoreceptor density is higher and the applied film is thinner. Those are rules of thumb from sensory work on abrasives and pigments rather than measured limits for your formula, so use them to set direction, not to certify a batch. Allantoin crystallises as angular prisms and needles, which are detected below the threshold a rounded particle of the same diameter would need, so err small. The comparison with a hard wax that failed to disperse is instructive: gritty balm from hard wax at least resolves on a remelt, and allantoin grit does not.

Dispersing it without grit

Heat does not help. Hot oil dissolves no more allantoin than cold oil, and it thins the vehicle so the powder settles faster. The right sequence is a cold slurry and a fast set.

1. Buy micronised material and keep it dry. Allantoin cakes in a humid workshop, and a caked lump will not disperse. Store it sealed with the rest of your powders, and see moisture control for the workshop side.
2. Weigh into a small portion of liquid oil at room temperature. Five to ten times the powder weight is enough. A light, thin oil disperses better than a viscous one at this stage.
3. Break the agglomerates properly. Grinding the slurry in a mortar, or a minute with a small homogeniser, does more than any amount of stirring. Most reported grit is agglomerated micronised powder, not oversized primary crystals.
4. Add the slurry to the melted base at the lowest temperature that stays fluid. Typically 60 to 65 C for a beeswax balm. There is no benefit to adding it into a 80 C melt.
5. Keep stirring while it cools, and pour late. Stir until the viscosity climbs noticeably, then pour at the top of your normal window. See pour temperatures for the trade against surface finish.

The reason for the late pour is sedimentation. Allantoin has a crystal density near 1.45 g/cm3 against roughly 0.91 for a warm oil blend. Put those into Stokes law with a 10 micrometre particle in an oil of about 50 mPa s and you get a settling speed of roughly 2 mm per hour, which is more than enough to strip the top of a tin over a slow cool. Nothing stops that except the yield stress of the wax network as it builds, which is why crystallisation and cooling rate and rheology and yield stress are the pages that actually govern whether your active ends up evenly distributed.

Needle crystals that appear days after the pour

A batch that was smooth when poured can turn scratchy by day three or four. That is recrystallisation, and it has two usual causes.

The first is dissolving the allantoin hot in a small polar phase. Solubility in water goes up roughly tenfold between 25 C and boiling, and glycerin behaves the same way, so a maker who warms glycerin, stirs in allantoin until it goes clear, and blends the result into a balm has made a supersaturated solution. As it cools and sits, the excess comes back out, and because it comes out slowly it grows long needles rather than fine particles. Slow growth from solution produces the worst crystal habit you can get.

The second is moisture picked up later. A balm stored in a warm bathroom, or one made with a damp botanical, gives dissolved allantoin somewhere to go and then somewhere to grow. That mechanism sits alongside the other problems in water contamination in balm.

How much to use in an anhydrous balm

The honest working range in a balm is 0.2 to 1 percent by weight. Below 0.2 percent you cannot weigh it reliably or justify it. Above about 1 percent the grit risk climbs faster than any benefit, because you are adding more insoluble solid to a vehicle that cannot take it into solution. Note the tension with the monograph: the US skin protectant floor is 0.5 percent, so anything below that is a cosmetic inclusion and cannot carry the protectant claim.

Look at the per-container column and the weighing problem becomes obvious. Two-tenths of a gram on a 100 g batch is at or below the resolution of the 0.01 g scale most small makers own, and a 0.01 g scale is only trustworthy well above its lowest readable digit. That is the practical argument for the premix in the tip above, and the reason to read weighing and calibration before you trust a small addition at all. The batch calculator will scale the percentages to whatever batch you are actually making. Two formulas on the site are natural homes for it: gardener's hand salve and foot and heel balm, both thick, opaque and applied to skin that is already rough.

Heat, decomposition and safe melt handling

The solid is thermally robust at balm temperatures. It melts with decomposition around 230 C, roughly three times the hottest point of a normal process, so nothing you do in a bain-marie touches it. The figure to respect is the one for solution: in water, allantoin hydrolyses towards allantoic acid and eventually urea, slowly at ambient and appreciably as you approach and pass 100 C, and faster at alkaline pH than at its own mildly acidic one. In an anhydrous balm that pathway is closed because there is no water for it to happen in.

Which leaves the ordinary rule: keep the melt below about 80 C for the sake of the oils and any botanicals, and add the allantoin slurry late. The methods and their temperature control are compared in melting methods. Direct heat on a dry powder is the only genuinely bad move, and there is no reason to do it.

Comfrey derived against synthetic

Allantoin is the compound traditionally credited for the reputation of comfrey, Symphytum officinale, which is why comfrey salves are old and stubborn. The comparison is not close in practice. Purified allantoin is a defined compound at a defined dose. A comfrey infusion delivers an unknown and probably small quantity of allantoin, since the molecule is water soluble and poorly extracted into oil, along with everything else in the root, including pyrrolizidine alkaloids. Those alkaloids are the reason regulators have restricted comfrey preparations, with the European Medicines Agency warning specifically about pyrrolizidine alkaloid exposure from herbal products, and the reason several markets limit comfrey products to unbroken skin and short courses. The herb side of that argument is in arnica, comfrey and salve herbs, with a worked preparation in comfrey salve.

"Botanically derived" or "comfrey derived" allantoin is sold, costs more, and is chemically the same molecule. The INCI name is Allantoin either way, so a customer cannot read the source off a label, and neither can you without a supplier declaration. If the source matters for your positioning, get it in writing on the specification. What you must not do is infuse comfrey into oil, add nothing else, and imply a monograph level of allantoin on the pack. If you want to know what an infusion actually carries, start with herbal infused oils and the infusion calculator.

When it is worth the trouble

Set expectations honestly. Allantoin earned its monograph slot decades ago on a modest evidence base, and it is classed as a skin protectant rather than anything more ambitious. In a balm, the wax and oil film is already doing the protecting: the reduction in water loss you can measure comes overwhelmingly from occlusion, which is the subject of transepidermal water loss and occlusive, emollient and humectant. Adding 0.5 percent of a suspended powder to an already occlusive base is a small increment on top of a large effect, and no honest reading of the literature makes it the reason the product works.

The decision rule is short. Include allantoin if you sell into the US, want the skin protectant claim, and accept the drug labelling that comes with it. Include it if the product is a thick, opaque hand or foot balm where a micronised powder disappears into the base and the positioning genuinely calls for a named active. Skip it in a clear or lightly tinted lip balm, in anything rinsed off, and in any batch you cannot mill and weigh properly, because a gritty lip balm loses you more customers than a named active wins. If what you actually want is a soft-focus active with no grit risk at all, panthenol is a viscous liquid rather than a crystal and disperses without the particle size argument, while urea and keratolytics covers the crystalline actives that share allantoin's problem in a stronger form. The general rule for actives in an oil-only vehicle is in menthol, camphor and actives.

Reviewed and updated 6 September 2026. Spotted an error? Tell us and we will fix and log it.