Polyhydroxy acids are usually introduced as "gentler AHAs", which is accurate and also incomplete. The difference is not a formulation trick — it comes from the size of the molecule, and molecule size explains nearly everything about how a PHA behaves, what it can be combined with, and which claims it can carry.
Two members of the family do the commercial work: gluconolactone and lactobionic acid. Both are larger than glycolic acid by a wide margin, both are far more forgiving, and both carry a second function that the AHAs do not.
What makes an acid a PHA
A polyhydroxy acid has multiple hydroxyl groups on a larger molecular backbone. That structure produces two effects at once.
The first is size. A PHA molecule is substantially larger than glycolic or lactic acid, so it diffuses more slowly and produces a less immediate sensation on skin. The second is water affinity. Multiple hydroxyl groups make the molecule good at holding water, which means the acid contributes to hydration as well as to the exfoliating story.
Those two properties are the whole proposition. A PHA is a slower, wetter acid that a customer with reactive or drier skin is more likely to tolerate.
Gluconolactone
Gluconolactone is the workhorse of the family. It is water-soluble, it dissolves easily, and it is supplied as a crystalline solid that is straightforward to handle.
Three practical notes:
- It hydrolyses in water. Over time, gluconolactone converts to gluconic acid, and the conversion rate is temperature-dependent. That is a stability consideration rather than a defect: the material is sold and used as the lactone, and a hot, lengthy hold during processing will move the equilibrium. Add it late in the process and keep the batch cool.
- It is a good humectant. The polyhydroxy structure holds water, which is why the finished product tends to feel more cushioned than an AHA product at the same acid level.
- It is comparatively inexpensive, which makes it the economical way to get a PHA story into a product.
Lactobionic acid
Lactobionic acid is larger still — it is built on a disaccharide backbone — and it is the more expensive of the two.
Its practical characteristics follow from that size and structure. It is a strong humectant, it is very well tolerated, and its uptake is slower again. It is typically used where the positioning is explicitly about a gentle, hydrating acid product, and it is often paired with gluconolactone so that the two together cover both the acid story and the hydration story.
Solubility is good, and the material is stable in a normal cosmetic pH range. The main constraints are cost and the fact that its contribution is gradual, which means it needs a consumer test with a realistic duration to show anything.
Molecule size and why it changes everything
The size difference is the reason a PHA can be sold to a customer who has given up on acids.
Smaller acids penetrate quickly and produce a sharp, immediate sensation that some skin types do not tolerate well. Larger acids move more slowly and produce a much milder experience at the same free acid value. That is not a matter of formulation softening the product — it is the physics of diffusion.
The trade-off is equally real. A slower acid produces a slower, more gradual visible change, and a brand that promises a visible result in a week while formulating with a large molecule has set a claim the product cannot meet. Our AHA comparison article sets out the same relationship for the smaller acids, and the ordering is the same: bigger molecule, slower uptake, milder experience, more gradual result.
Humectancy: the second function
This is the part of the PHA proposition that the AHAs cannot match, with one exception — lactic acid is itself a humectant.
Because a PHA carries multiple hydroxyl groups, it holds water in the finished product and on the skin. That means a PHA serum can be positioned around two benefits at once: the appearance of refined texture and the appearance of hydrated, comfortable skin. The two are mutually reinforcing in a marketing sense, and they are both appearance claims, which keeps the product inside the cosmetic zone.
In practice this is why PHA products so often look like hydration products with an acid in them rather than acid products with a humectant added. The formula reads as a comfort serum, and the acid is one of several things going on.
pH and the free acid question
The free acid relationship applies to PHAs exactly as it does to the smaller acids: the fraction of material in the undissociated form depends on pH relative to pKa, and it is that fraction which constitutes the useful dose.
What differs is the practical target. Because PHAs are positioned as gentle, formulators often work at a pH above the value used for a glycolic product, which further reduces the free acid value. The result is a product that is genuinely mild and also, objectively, delivering less acid. That is a legitimate design choice as long as it is a deliberate one and the claim matches it.
The failure mode is a brief that asks for "PHA at 10%" without specifying the pH. That specification can produce a product ranging from a meaningful acid serum to a slightly acidic moisturiser, and the label would look identical either way.
Market status and the restriction gap
One of the practical advantages of the family is that the restrictions written for the smaller AHAs do not apply in the same way.
Where a market imposes a maximum concentration and a minimum pH on at-home AHA products, that restriction is written around the defined AHA list, and PHAs typically fall outside it. This is a meaningful commercial difference: it allows a higher use level, or a lower pH, or a claim that a restricted AHA product could not carry in that market.
None of which removes the obligation to test. A product that is unrestricted is still a product that has to be safe in use, and the fact that a molecule is large does not make it inert. The market-by-market picture also keeps changing, and since this is exactly the kind of point where copying a number from an article goes wrong, the position should be confirmed for the specific markets you are launching in rather than assumed. Our labelling guide and reformulation article cover how that is handled.
The three acid families compared
| Property | AHA (glycolic / lactic) | PHA (gluconolactone / lactobionic) | BHA (salicylic) |
|---|---|---|---|
| Relative molecule size | Smallest | Large | Small |
| Uptake and sensation | Fast, sharper | Slow, mildest | Fast, often drying |
| Humectancy | Only lactic acid | Both members | None |
| Water solubility | Very high | High | Limited; needs a carrier |
| Market restrictions | Commonly capped with a pH floor | Usually outside the AHA caps | Commonly capped, with age conditions |
| Best fit | Positioning built around visible results | Reactive or drier skin; hydration-led products | Blemish-prone positioning |
Formulation notes
- Add gluconolactone late and cool. Hydrolysis to gluconic acid is temperature-driven, and a long hot hold shifts the balance before the product is even filled.
- Watch the electrolyte load. A high acid level in a polymer-thickened base changes the viscosity, and PHA levels are often high by design. See our viscosity article.
- Keep the preservation work real. Humectant-rich, mildly acidic bases are not automatically self-preserving, and the water activity is not low enough to carry the product. See our preservative article.
- Check pack compatibility where the pH is acidic and the pack contains metal components — see our packaging article.
- Expect a texture decision. A high PHA level with good humectancy produces a product that is thicker and slightly tackier than a glycolic serum, and that is part of the positioning rather than a defect to be engineered away.
Claims
The family supports appearance claims: skin looks smoother, texture looks more refined, the surface looks more even, and skin looks and feels hydrated and comfortable. Because the acid is slower, claims about comfort and hydration are easier to support than claims about a rapid visible change.
The boundary is the same as for any acid: no treatment language, no condition language, no comparison to a professional procedure, and no implication that the product thins or removes skin. Our efficacy testing article covers how the permitted versions are structured.
Testing to commission
- pH at release and across stability, reported as a value.
- Assay on the acid, and for gluconolactone a check on the lactone-to-acid ratio at release and at the end of the stability period.
- Preservative efficacy on the finished formula at its actual pH.
- Viscosity across stability.
- Consumer use testing over a realistic period, asking about comfort and sensation as well as appearance.
Where our capability fits
We formulate gluconolactone and lactobionic acid systems in aqueous serums, hydrating essences and capsule fills, with the pH and the free acid value specified together. Examples include a custom cosmetic softgel face serum capsule and a hydrating soothing repair face cream.
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 skin type you are targeting and how fast the claim needs to be, and we will come back with the acid level and the pH that match. 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 concentration limits vary by market.