PHA in K-Beauty: Gluconolactone and Lactobionic Acid Ingredient Guide

Exfoliating toners used to mean glycolic acid, a tingle and a sunburn warning. Many newer K-beauty toners, pads and creams use a gentler family of acids instead: polyhydroxy acids, or PHAs.

On a spec sheet, a PHA looks like an easy swap. Replace the glycolic acid with gluconolactone, call the product gentle, done. In the lab it is less simple. Gluconolactone keeps changing the pH of a formula after it is mixed. It can push a common preservative out of solution. And the US label guidance for acids was written with AHAs in mind.

Below: what PHAs are, how the two main ones differ, what the research supports, and how to brief a Korean ODM.

What Is a PHA, and Why Do Korean Labs Use It?

A polyhydroxy acid (PHA) is a hydroxy acid that carries several hydroxyl groups along its chain. Gluconolactone is the classic example. Lactobionic acid is a bionic acid, which is a PHA bonded to a sugar, and brands usually market it as a PHA too. A 2009 review in Clinics in Dermatology groups them this way. It credits them with AHA-type benefits and less irritation, which suits sensitive skin and skin after procedures (Green, Yu and Van Scott).

That profile is why labs reach for PHAs when a brief asks for exfoliation without much sting. The molecules are larger than glycolic acid and hold water well, so the same ingredient can exfoliate and moisturize at once.

One detail matters at the label stage: gluconic acid has a hydroxyl group in the alpha position, the feature that gives AHAs their name. A PHA is a close cousin of an AHA.

Gluconolactone and Lactobionic Acid Do Different Jobs

Gluconolactone is the exfoliating workhorse: it dissolves in water and slowly turns into gluconic acid, which lowers the pH. Lactobionic acid is the hydration specialist: it holds water and acts as an antioxidant by binding metals. Pick by the job the product has to do.

The origin row matters for marketing. Lactobionic acid starts from lactose, so a vegan claim needs the supplier's written statement on feedstock and processing before you print it. Our vegan and cruelty-free certification guide for Korean manufacturing covers that paperwork.

How Does PHA Compare With AHA and BHA?

PHAs sit at the gentle end of the acid family. AHAs such as glycolic acid exfoliate harder and come with FDA sun-sensitivity guidance. BHA, mainly salicylic acid, is the oil-soluble option positioned for pores. All three exfoliate; they differ in strength, labeling and positioning.

The last row is not a free pass. Your regulatory reviewer still has to decide on sun wording, covered in the claims section below.

What the Research Supports So Far

The evidence for PHAs is real but thinner than the evidence for glycolic acid. It supports gentler exfoliation, moisturizing and, in a lab model, some protection against UV-related changes. It does not support drug-like claims.

In a 2004 study in Dermatologic Surgery, gluconolactone partly protected against UV-induced changes in a lab model of skin photoaging (Bernstein et al.). A human test in the same paper found no significant increase in sunburn cells after use. That is a useful contrast with glycolic acid, which FDA's own research linked to higher UV sensitivity (FDA).

A 2019 review in the International Journal of Dermatology calls lactobionic acid a strong moisturizer. It also works as an antioxidant by binding metals and slowing collagen-degrading enzymes (Algiert-Zielinska et al.).

Some early PHA data comes from small studies and a conference poster cited in supplier literature. Treat words like "clinically proven" with care, and plan the testing that backs "gentle" or "for sensitive skin" before the artwork is final.

Why Does pH Drift in a Gluconolactone Formula?

Gluconolactone is a cyclic ester of gluconic acid. In water it slowly hydrolyzes into gluconic acid, so the pH keeps falling after the ingredient goes in, and heat speeds that up. A pH reading taken at the start of a batch is not the pH that ships (Jungbunzlauer formulation guide).

The guide recommends adjusting pH at the end of production, or adjusting early and correcting again at the end. Overshooting early with extra base caused phase separation in its emulsion trial, and hot processing for creams speeds the hydrolysis.

The guide also maps which form dominates at which pH. Around pH 3.6, gluconic acid and its salt form are present in equal amounts. Exfoliation is favored in acidic conditions below pH 4.5, while metal binding gets stronger above about pH 4. Same percentage, different pH, different product.

In the brief, that becomes one line: a target final pH range, reported at the end of production and at every stability pull.

Preservation and Packaging Decide Whether It Survives

Low pH changes how preservatives behave. Salt-type preservatives such as sodium benzoate turn into their acid form when gluconolactone pulls the pH below the preservative's pKa, and that acid form can crystallize (Jungbunzlauer). Ask the lab for a preservative system chosen for your final pH, then a challenge test.

In that supplier's serum trial, a version preserved with sodium benzoate and potassium sorbate crystallized, while one with benzyl alcohol and caprylyl glycol stayed stable. Preservation has to be tested in the real formula at the real pH.

Preservative efficacy testing under ISO 11930 is the standard check for a water-based product. Our guide to reading Korean ODM stability and ISO 11930 reports shows what a passing result should look like.

Pads add their own risks. A jar of soaked pads is opened again and again, so test the full package in use, including evaporation late in shelf life. The K-beauty toner pads sourcing guide covers pad materials and jar formats.

Which Claims Keep a PHA Product a Cosmetic in the US?

Claims about appearance keep a PHA product a cosmetic: smoother texture, a brighter look, a softer feel. Claims to treat acne, remove scars or lighten discoloration make it a drug under FDA rules (FDA on AHA products and drug claims).

If acne is the real goal, the US route is an OTC drug built on a monograph active such as salicylic acid, not a PHA cosmetic. Our salicylic acid acne products and FDA OTC guide walks through that path.

Sun wording needs a decision too. FDA's guidance asks for a Sunburn Alert on cosmetics that contain an AHA as an ingredient (FDA AHA labeling guidance). PHAs are not named, and the Bernstein data points away from glycolic-style sun sensitivity. Because of the alpha-hydroxyl group, a short sun-protection direction is still the conservative choice. Decide with your reviewer and note the reasoning in your safety file.

MoCRA adds the baseline duties: product listing, facility registration and records that support each product's safety (FDA MoCRA overview). Our FDA requirements guide for Korean skincare imports covers registration, listing and labels step by step.

Five Lines to Put in Your Korean ODM Brief

A PHA brief needs five specifics: which PHA and how much, the final pH, the preservative plan, the stability plan and the claims. Each line closes a gap that otherwise shows up as a reformulation round.

1. PHA choice and level. Name gluconolactone, lactobionic acid or both, and ask for the supplier's spec sheet and origin statement.
2. Final pH. Give a target range and ask for pH measured at the end of production and at each stability pull.
3. Preservative system. Ask how it was chosen for a low-pH formula and request an ISO 11930 challenge test on the final formula.
4. Stability in the final package. Heat and cold cycling that tracks pH, color, odor and crystals, plus evaporation for pads.
5. Claims and label. List every planned claim and decide the sun-protection direction before artwork.

If the concept pairs a PHA with a soothing botanical, our heartleaf (Houttuynia cordata) ingredient sourcing guide covers one well-known Korean option.

Frequently Asked Questions

What pH should a PHA toner be?
No single legal number applies to PHAs. Jungbunzlauer's formulation guide says gluconolactone exfoliates best below pH 4.5 and suggests working around pH 3.6 (Jungbunzlauer). For glycolic and lactic acid, the CIR safety conditions FDA cites include a final pH of 3.5 or higher (FDA). Set a range with your chemist and confirm it after production.

Do PHA products need a Sunburn Alert in the US?
FDA's guidance names AHA ingredients, not PHAs, so it is a judgment call. Gluconic acid still carries an alpha-hydroxyl group, and a label is hard to change after printing. Adding a short sun-protection direction is the conservative choice.

Can a PHA toner claim to treat acne?
Not as a cosmetic. A product intended to treat acne is a drug in the US, and an OTC acne product has to use an active the monograph allows, such as salicylic acid. Keep PHA claims to appearance: smoother, softer and more radiant-looking skin.

Is lactobionic acid better than gluconolactone for dry skin?
Lactobionic acid is usually chosen when moisture is the main goal. A 2019 review describes it as a strong humectant with antioxidant activity (Algiert-Zielinska et al.). Gluconolactone also moisturizes but is picked mainly for gentle exfoliation.

By Liz Song, K-beauty sourcing consultant.