Introduction to Polyhydroxy Acids in Cosmetic Formulation
Polyhydroxy acids are among the most formulator-friendly chemical exfoliants available today. They deliver progressive surface exfoliation, meaningful humectancy, and antioxidant activity, all while maintaining a skin tolerance profile that most AHAs cannot match.
This guide covers everything a cosmetic formulator needs to know about working with PHAs, from INCI names and usage rates to pH management, compatibility, and finished product applications across rinse-off and leave-on formats.
What Is a Polyhydroxy Acid Cosmetic Ingredient?
A polyhydroxy acid is a type of chemical exfoliant characterized by multiple hydroxyl (OH) groups attached to its molecular structure. These extra hydroxyl groups give PHAs a significantly larger molecular size compared to alpha-hydroxy acids (AHAs) and beta-hydroxy acids (BHAs).
The larger molecule slows dermal penetration, which is what makes the polyhydroxy acid category distinctly gentler than AHAs at equivalent pH levels.
PHAs fall under the Active category in cosmetic formulation. They function simultaneously as exfoliants, humectants, and antioxidants, making them multifunctional actives suited to a wide range of product formats.
The three most commercially relevant PHAs in cosmetic formulation are:
- Gluconolactone (INCI: Gluconolactone)
- Lactobionic Acid (INCI: Lactobionic Acid)
- Maltobionic Acid (INCI: Maltobionic Acid)
Each shares the same foundational PHA mechanism but differs in molecular origin, availability, and minor formulation behavior, which is covered in detail further below.
How Polyhydroxy Acids Function in Cosmetic Formulation
Primary Function
PHAs work by loosening corneocyte cohesion within the outer layers of the stratum corneum. This promotes the natural shedding of dead skin cells and may help improve the appearance of skin texture, tone, and surface smoothness over consistent use.
Humectant Activity
The multiple hydroxyl groups in their molecular structure attract and bind water molecules. This gives PHAs genuine humectant function within the same ingredient, unlike AHAs which exfoliate without contributing meaningful hydration.
Antioxidant Function
PHAs, particularly lactobionic acid and gluconolactone, have demonstrated free radical scavenging activity in published cosmetic literature. This supports the appearance of skin resilience against environmental stressors such as UV exposure and pollution.
Chelating Properties
Several PHAs can bind divalent metal ions such as iron and calcium. This chelating action benefits both the skin surface and the formula itself by reducing metal-catalyzed oxidative damage.
Why Formulators Choose PHAs
PHAs are selected when gentle chemical exfoliation is required for sensitive, reactive, rosacea-prone, mature, or post-procedure skin formulas. Their combined exfoliant and humectant function also allows for a more efficient ingredient list compared to using separate actives for each role.
Recommended Usage Rate for Polyhydroxy Acids
| Product Type | Typical Usage Range |
| Leave-on exfoliating serum | 3% to 10% |
| Leave-on moisturizer or cream | 2% to 5% |
| Toner or essence | 2% to 8% |
| Rinse-off cleanser | 1% to 3% |
| Leave-on or wash-off mask | 3% to 8% |
| Eye area products | 0.5% to 2% |
| Professional or post-procedure use | Up to 15% |
Start at the lower end of the range and evaluate skin tolerance before scaling concentration upward.
Efficacy is pH-dependent, not purely concentration-dependent. Always confirm and adjust formula pH before modifying usage rate. A well-formulated 5% PHA serum at pH 3.8 will outperform a poorly adjusted 10% formula at pH 6.0.
Solubility and Phase Information
All three major PHAs are water soluble. They must be incorporated into the aqueous phase of emulsions and water-based systems.
They are not suitable for anhydrous formulas such as balms, sticks, or oil serums where no water phase is present.
PHAs dissolve at room temperature and do not require heat activation. This makes them ideal for cool-down addition, preserving ingredient integrity in heat-sensitive formulations.
In emulsions, add PHAs to the water phase at temperatures below 70°C. Sustained high-heat exposure above 80°C may initiate hydrolytic degradation.
Because PHAs are acids, they will lower the pH of the water phase upon addition. Always measure and record pH after incorporation before combining phases.
pH Range and Stability of Polyhydroxy Acids
Ideal pH Range: 3.5 to 4.5 for maximum exfoliant activity.
At this range, the free acid form predominates and delivers its exfoliating function at the skin surface. Above pH 5.5, a significant portion converts to the salt form, substantially reducing exfoliant activity.
For formulas targeting humectant or antioxidant benefits without pronounced exfoliation, a working pH of 5.0 to 6.0 is acceptable with that trade-off clearly understood.
Stability Notes
Avoid sustained processing temperatures above 80°C after PHA addition to prevent hydrolytic breakdown.
PHAs show reasonable light stability compared to some AHAs, but opaque or UV-protective packaging remains best practice for any active-containing formula.
Including a chelating agent such as tetrasodium EDTA or phytic acid in the formula further protects both the PHA and the overall system from metal-catalyzed oxidation.
Properly formulated and packaged products typically achieve a shelf life of 12 to 24 months when stored below 30°C away from direct sunlight and heat sources.
Compatibility and Incompatibilities Polyhydroxy Acids
Compatible With
- Other PHAs, which can be combined in the same formula without conflict
- Niacinamide at moderate concentrations (below 5%) with careful pH management
- Hyaluronic acid and sodium hyaluronate as complementary humectants
- Panthenol and glycerin as supporting hydration actives
- Mild preservative systems such as phenoxyethanol, ethylhexylglycerin, and sodium benzoate at appropriate pH
- Ascorbic acid derivatives in low-pH serum formulas
- Peptides selected specifically for low-pH stability
Avoid Combining With
- High-concentration AHAs at exfoliant-active pH, as the cumulative acid load may exceed what a sensitive skin-positioned formula can support
- Strong oxidizing agents such as benzoyl peroxide, which may compromise both ingredient integrity and formula stability
- Cationic polymers such as polyquaternium compounds in rinse-off systems, where charge interactions may cause precipitation or cloudiness
- Alkaline ingredients and high-pH buffering systems that neutralize exfoliant activity
- Retinol or retinoids where combined irritation risk is a concern for retail-positioned products targeting sensitive skin
Polyhydroxy Acid Formulation Tips for Professionals
Best Product Formats
Leave-on serums, hydrating toners, and lightweight moisturizers are the most natural fit for PHAs. They also perform well in gel-cream formulations built on carbomer or hydroxyethylcellulose bases where water continuity is maintained throughout the system.
pH Adjustment
After dissolving PHAs in the water phase, adjust pH upward using a dilute 10% sodium hydroxide (NaOH) solution or triethanolamine in small, incremental additions. Always use a calibrated pH meter rather than pH strips for accurate formulation.
Common Formulation Mistakes
The most frequent error is adding PHAs without accounting for the pH drop they introduce. This results in a final formula far below the intended pH, causing stinging, packaging incompatibility, or compromised preservative efficacy.
Stacking multiple acids at high concentrations while marketing the product as sensitive skin appropriate is another common mistake. Cumulative acid load must always be considered alongside individual ingredient usage rates.
Processing Temperature
Add PHAs below 70°C. Cool-down addition at 40°C or below is preferable for premium formulations where ingredient integrity is a priority.
Sensory Profile
PHAs contribute minimal texture impact at typical usage rates. At higher concentrations, mild tackiness may be noticeable due to the multiple hydroxyl groups. This can be balanced through appropriate emollient selection in the oil phase of an emulsion.
Individual PHA Profiles: Gluconolactone, Lactobionic Acid, and Maltobionic Acid
Gluconolactone
Gluconolactone is the most commercially available PHA and the most widely documented in peer-reviewed cosmetic literature.
It is derived from gluconic acid and has a slightly smaller molecular size than lactobionic acid, meaning marginally faster penetration, though it remains firmly in the gentle-exfoliant category.
It is the most cost-accessible PHA for independent formulators and small brands. It is the go-to starting point for most PHA formulations.
Lactobionic Acid
Lactobionic acid is derived from the oxidation of lactose and carries the largest molecular size among the three major PHAs. This makes it the gentlest of the group in terms of penetration rate.
It is the preferred choice for post-procedure formulas and products explicitly targeting compromised or highly reactive skin. It also has the strongest documented antioxidant and chelating activity within the PHA family.
For a full technical breakdown, refer to the Lactobionic Acid ingredient entry in the formulachemistry Encyclopedia.
Maltobionic Acid
Maltobionic acid is derived from maltose and is structurally almost identical to lactobionic acid in molecular size and function. It is considered interchangeable with lactobionic acid in most formulation contexts.
Its primary limitation is commercial availability. It is less widely stocked than gluconolactone or lactobionic acid and is typically priced higher. Formulators in markets with reliable supply chains for maltobionic acid will find it a strong performer.
Skin Benefits of Polyhydroxy Acids in Cosmetic Products
- May help improve the appearance of skin texture and surface smoothness through gentle, progressive exfoliation
- Supports the appearance of a more even skin tone with consistent use in appropriately formulated products
- May help improve the appearance of skin hydration through genuine humectant activity
- Commonly used to support the appearance of skin resilience through antioxidant function
- Considered appropriate for formulations addressing the appearance of sensitive, mature, rosacea-prone, or post-procedure skin
- May support the appearance of refined pore texture and smoother skin surface over time
Common Product Applications for Polyhydroxy Acids
PHAs appear across a broad range of cosmetic product categories wherever gentle chemical exfoliation, antioxidant activity, or humectant-active function is the formulation goal.
- Leave-on exfoliating serums and treatment essences
- Daily-use hydrating toners and pH-balancing mists
- Moisturizing creams and gel-creams for sensitive or mature skin
- Eye area serums and creams at lower concentration ranges
- Sheet masks and hydrogel masks
- Post-procedure recovery creams and barrier support formulas
- Gentle daily exfoliating cleansers in rinse-off formats
- Brightening ampoules and concentrated treatment actives
- Scalp serums for surface exfoliation, an emerging but growing application
PHAs vs. AHAs vs. BHAs: Formulation Comparison
Understanding where PHAs sit relative to AHAs and BHAs is essential for making informed ingredient selection decisions.
| Property | PHAs | AHAs | BHAs |
| Molecular Size | Large | Small to medium | Medium |
| Penetration Speed | Slow | Fast | Medium |
| Irritation Potential | Low | Medium to high | Medium |
| Humectant Activity | Yes | Minimal | No |
| Antioxidant Activity | Yes | No | No |
| Suitable for Sensitive Skin | Yes | With caution | With caution |
| Oil Soluble | No | No | Yes (salicylic acid) |
| Typical Active pH Range | 3.5 to 4.5 | 3.0 to 4.5 | 3.0 to 4.0 |
This comparison makes clear why PHAs are the preferred exfoliant active for formulas targeting sensitive, reactive, or compromised skin. The trade-off is that PHAs work more progressively than AHAs, which may be a consideration for formulas where faster visible results are the primary claim.
Substitutes and Alternatives to Polyhydroxy Acids
Mandelic Acid is the gentlest AHA and the closest alternative to PHAs in terms of skin tolerance. Its larger molecular size relative to glycolic or lactic acid slows penetration, though it still carries a higher irritation risk than PHAs. Suitable for formulators who require an AHA classification in their product story.
Lactic Acid is a mid-range AHA that also provides some humectant activity due to its role as a natural moisturizing factor (NMF) component. It is gentler than glycolic acid but more irritating than any PHA. Appropriate where moderate exfoliation at lower pH is the goal and sensitivity is less of a concern.
Glycolic Acid is the smallest and most penetrating AHA, delivering the strongest exfoliant effect but with the highest irritation potential in the acid exfoliant category. Not a true substitute for PHAs in sensitive skin formulas, but relevant for comparison when formulators are evaluating the full acid exfoliant spectrum.
Safety and Regulatory Notes for Polyhydroxy Acids
PHAs have a well-established safety record based on decades of clinical use, peer-reviewed research, and consumer product data. They are broadly regarded as the safest category of chemical exfoliants available for retail cosmetic formulation.
Irritation Potential: Low relative to AHAs at equivalent pH. Individual variation still applies, and concentrations above 10% in leave-on products or pH below 3.5 will increase irritation risk.
Patch Test: A patch test recommendation is good practice on all finished products containing PHAs, particularly those positioned for sensitive skin segments.
Eye Area: Avoid direct eye contact at concentrations above 2%. Periorbital formulas should be developed at the lower concentration range and confirmed through appropriate ophthalmological assessment.
Broken Skin: Avoid application to actively broken, abraded, or inflamed skin. Acid application to a disrupted skin barrier may cause stinging or sensitization regardless of the acid’s general tolerance profile.
Regulatory Status: All three major PHAs are permitted for cosmetic use under EU Cosmetics Regulation 1223/2009, FDA cosmetic ingredient classification in the US, and major global regulatory frameworks. No blanket concentration restrictions currently apply under standard cosmetic regulations.
Sun Sensitivity: As with all exfoliating actives, finished products should include a recommendation to use broad-spectrum sun protection during and after use, particularly for leave-on formats applied in the daytime.
Related Ingredients on formulachemistry
Lactobionic Acid is the most technically detailed individual PHA covered in the formulachemistry Encyclopedia. Formulators building post-procedure or sensitive skin formulas should review its full ingredient entry alongside this guide.
Glycolic Acid is the AHA most commonly compared to PHAs in formulation education. Understanding its mechanism and limitations provides important context for positioning PHAs correctly in product development and brand communication.
Niacinamide is the most frequently paired active alongside PHAs in brightening and texture-refining formulations. Both are water soluble and compatible at appropriate pH, making them a well-established combination in the sensitive skin segment.
Frequently Asked Questions About Polyhydroxy Acids
What is the ideal pH for polyhydroxy acids in cosmetic formulas?
The optimal working pH range is 3.5 to 4.5 for full exfoliant activity. Above pH 5.5, the free acid form converts largely to its salt, significantly reducing exfoliant function.
Are polyhydroxy acids safe for sensitive skin?
Yes. PHAs are consistently cited in cosmetic literature as the preferred chemical exfoliant for sensitive, reactive, and rosacea-prone skin due to their large molecular size and slow penetration rate.
What is the difference between PHAs and AHAs?
PHAs have a larger molecular size than AHAs, which slows skin penetration and reduces irritation risk. PHAs also offer humectant and antioxidant activity that AHAs do not provide.
Can polyhydroxy acids be used around the eye area?
Yes, at reduced concentrations. Usage rates of 0.5% to 2% are appropriate for periorbital applications. Formulas intended for the eye area should always be assessed through appropriate ophthalmological testing before retail release.
Which PHA is best for post-procedure formulas?
Lactobionic acid is the preferred choice for post-procedure applications due to its large molecular size, low irritation profile, and the strongest antioxidant and chelating activity within the PHA family.
Are polyhydroxy acids oil or water soluble?
All major PHAs are water soluble only. They must be incorporated into the aqueous phase and are not suitable for anhydrous or oil-continuous systems.
Conclusion
Polyhydroxy acids are a technically sound, clinically supported category of cosmetic actives that belong in every formulator’s working ingredient knowledge.
- Primary Role: Gentle chemical exfoliant, humectant, and antioxidant active
- Category: Active, Polyhydroxy Acid
- Key Members: Gluconolactone, Lactobionic Acid, Maltobionic Acid
- Recommended Usage Rate: 2% to 10% leave-on; 1% to 3% rinse-off