Azelaic acid is a powder. That sounds like a trivial detail until you try to put a meaningful level of it into a clear serum, at which point it becomes the defining constraint on the whole project. It dissolves poorly in water, it dissolves poorly in most oils, and when it is dispersed instead, it can feel gritty on the skin.
The result is a category where the formulation work is mostly dispersion work, and where two products with the same declared percentage can feel entirely different to the customer.
A powder problem before it is a chemistry problem
The first question in an azelaic acid brief is not what pH to target. It is which physical form the material will take in the finished product.
There are three possibilities, and they lead to three different products:
- Dissolved. Requires a solvent system that can carry the level, which in practice means a glycol-rich or surfactant-containing base. Gives a clear or translucent product but constrains the sensory profile.
- Dispersed. The powder is suspended in the base with a dispersing aid. Gives a soft, opaque product and a much freer choice of base, at the cost of a settling study and a particle-size requirement.
- Emulsified into an oil phase. Workable where the material can be incorporated into the oil phase during processing, and common in cream formats.
Deciding this at the start is what makes the rest of the project straightforward. Deciding it after the sensory target has been fixed is what causes a reformulation round.
What azelaic acid is and why it is difficult
Azelaic acid is a straight-chain dicarboxylic acid — nine carbons, with a carboxylic acid group at each end. That structure explains the behaviour.
Two carboxylic acid groups make the molecule polar and give it a high melting point, which is why it is a crystalline solid at room temperature and why it does not dissolve readily in either water or oil. It is also a weak acid, so it can be partially converted to a salt, and the salt forms are considerably more water-soluble than the free acid.
The salt route is the standard way to get a higher level into an aqueous product, and it introduces the same trade-off that appears with every acid in this category: the dissolved form is often the salt, while the free acid is the form the positioning is built around.
Solubility: the numbers that shape the format
The practical consequence of the solubility limit is that a clear aqueous serum carrying a high level of azelaic acid is difficult to produce without a substantial glycol or surfactant load.
That pushes formulators towards a few answers:
- Moderate level in a glycol-rich clear base. Achievable, and it feels like a serum — but the glycol load is doing the work, and it changes the sensory result.
- Higher level in a cream or lotion. The powder is incorporated into the oil phase or dispersed in the emulsion, and the level is no longer limited by water solubility.
- Derivative routes. Materials such as azelaic acid derivatives are supplied specifically to improve solubility and sensory behaviour. They are legitimate ingredients with their own INCI names, and they are not the same material — if the pack names azelaic acid, the derivative does not count.
The most common commercial answer is a cream or a gel-cream, because that is where the level and the sensory result can both be achieved. Our emulsion formulation article covers the base decisions.
Dispersion routes and particle size
Once the decision is to disperse rather than dissolve, particle size becomes the specification point that determines whether the product feels acceptable.
Coarse particles settle faster, feel gritty on application, and produce a product that separates visibly in the pack. Finer particles stay suspended longer and feel smooth, at the cost of a more demanding milling or sourcing requirement and a greater tendency to agglomerate if the dispersion is done badly.
The dispersion step itself matters as much as the particle size. Powder added to a base without adequate wetting will form lumps that no amount of subsequent mixing fully breaks up, and those lumps are what the customer feels. The standard practice is to pre-wet the powder in a portion of the oil phase or in a glycol, then add that premix to the main batch under shear.
For a capsule format, the dispersion has to be stable at the point of filling as well as in the finished capsule, which is the same homogeneity requirement described in our fill weight article.
The grittiness problem and how to test for it
Grittiness is the single most common complaint about this category, and it is testable before launch.
Three checks do most of the work. A microscopic examination of the bulk confirms that the powder is dispersed rather than agglomerated. A particle-size distribution on the raw material confirms that the incoming specification matches what the dispersion was designed for. And a trained sensory panel, or a small consumer panel, applies the finished product and reports on feel — which catches the cases where the particle size is technically in range but the sensory result is still not acceptable.
The sensory check is worth insisting on for a specific reason: the threshold at which a customer perceives grittiness is not the same as the particle-size threshold that a specification would naturally use. Only a person applying the product can answer the question that matters.
pH and the salt question
Because azelaic acid is a weak acid with two acid groups, its state in the formula depends on pH in the same way as the other acids in this category: below the relevant pKa, more of the material is undissociated; above it, more is in the salt form.
For a dispersed product the relationship is more complicated than for a dissolved one, because the material is largely present as a solid phase rather than in solution, and the pH of the continuous phase is partly set by the small dissolved fraction. The practical approach is to set the pH of the base deliberately, confirm it at release and across stability, and treat the free acid calculation as a design input rather than a precise dose.
The same free acid logic that applies to the AHAs is the right mental model — see our AHA article — with the added caveat that a suspension is not a solution.
Market status: the cosmetic and the regulated boundary
This is the point where an azelaic acid project has to stop and check the market before going further.
In some markets the material is an ordinary cosmetic ingredient. In others, products containing it at levels associated with a specific function, or carrying claims in that direction, are treated as a regulated category with its own approval route rather than a cosmetic notification. The threshold and the claim language that triggers it differ between markets.
Because the difference is one of category rather than of degree, it cannot be resolved with a labelling change or by reducing the level slightly. It has to be settled at the start, alongside the claim. Our reformulation article covers what changing markets after the fact involves, and our blemish-prone skin article covers the claim boundary.
Dispersion routes compared
| Route | Product appearance | Level achievable | Main risk |
|---|---|---|---|
| Dissolved in a glycol-rich base | Clear to translucent | Moderate | Glycol-heavy sensory profile |
| Dispersed in a cream or lotion | Opaque | Higher | Grittiness and settling |
| Incorporated into the oil phase | Opaque, rich | Depends on the oil system | Recrystallisation on cooling |
| Solubilised derivative | Clear | Depends on the material | Not the same ingredient as the parent acid |
Stability and the settling question
A dispersed product needs a stability protocol that includes a settling observation, and the observation has to be made in the retail pack.
Look for three things: whether the powder settles to a visible layer, whether it re-disperses on shaking, and whether the particle size has changed over time through agglomeration or crystal growth. Recrystallisation is a real mechanism for a material with a high melting point, and it shows up as a change in feel rather than a change in appearance.
The general stability schedule in our stability article applies, with the settling and particle checks added. Preservation also still applies — a dispersed powder is not a preservative, and the water phase needs a tested system; see our preservative article.
Claims
The available claims are appearance and feel claims: skin looks more even, the surface looks refined, pores look less visible, skin looks clearer and feels smoother.
Anything describing treatment of a skin condition, inflammation, or a comparison to a medicinal product is outside the cosmetic zone. This boundary matters more here than for most ingredients because the market position of azelaic acid is close to the regulated category, and the claim is what decides which set of rules the product falls under. Our efficacy testing article covers how the permitted versions are substantiated.
Testing to commission
- Particle size distribution on incoming material against the specification the dispersion was designed for.
- Microscopic dispersion check on the bulk at release.
- Settling and re-dispersion observation in the retail pack at every stability point.
- Viscosity across stability, since a changing particle network changes the flow — see our viscosity article.
- pH at release and across stability.
- Preservative efficacy on the finished formula.
- Sensory evaluation by untrained users, specifically for grit.
Where our capability fits
We formulate dispersed and emulsion-based azelaic acid systems with the particle size and the dispersion method specified, and with the settling study built into the stability protocol. Examples include a custom cosmetic softgel face serum capsule and a facial essence capsule.
We work with brands on private label (your brand on a proven base), OEM/ODM contract manufacturing, and full custom formula development — whichever matches where your brand is today.
Tell us the market, the format and how the product needs to feel, and we will come back with the dispersion route and the particle specification. Start at our inquiry page, email capsulebiotech@163.com, or message the right team on WhatsApp: Capsule Series (capsules only) +86 158-7655-5319, Cosmetics Series (serum, hair care, body care, fragrance) +86 158-7655-5319.
General manufacturing information, not regulatory or legal advice. Ingredient status and claim limits vary by market.