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Polyhydroxy acids (PHAs)

Also known as: PHAs, gluconolactone, lactobionic acid, polyhydroxy bionic acids

Polyhydroxy acids are a group of skincare ingredients used to support surface exfoliation and moisture retention. Gluconolactone and the related bionic acid lactobionic acid are common examples. Their effects depend on the particular acid and the finished formulation.

In plain English — PHAs are skincare ingredients used to help smooth and moisturise the skin's surface. Small studies of particular gluconolactone and lactobionic acid products support these skincare roles. The choice depends on the complete product and the skin's condition, rather than the word PHA alone.

Evidence status

Emerging

Human studies support particular hydration, skin-surface pH and acne outcomes for selected formulations. The evidence is heterogeneous, and short biophysical studies do not establish a class-wide treatment effect for sensitive or diseased skin.

What polyhydroxy acids are, and the types available#

Polyhydroxy acids have several hydroxyl groups in their chemical structure. Gluconolactone is a commonly used representative. Lactobionic acid belongs to the related polyhydroxy bionic-acid group, in which the structure also includes a sugar component. Skincare discussions often place both under the PHA umbrella.[1]

These ingredients appear in moisturising formulations, exfoliating solutions and combination products. A leave-on emulsion and a professional peel have different purposes even when they name the same acid. The subject here is the ingredient family; chemical peels covers procedural assessment.[1, 3]i

Use of polyhydroxy acids in aesthetic practice#

The practical cosmetic aims are improved surface feel and moisture, with selected products also studied for photoageing or acne-related concerns. A useful consultation separates dryness or roughness from an active eruption, identifies previous reactions, and establishes what the proposed product is intended to change.[1, 3, 6]i

PHAs may be considered where comfort is important, using evidence for the complete product. In clients receiving medical treatment, supportive skincare should fit the existing clinical plan; an exfoliant is not the diagnosis or the whole management strategy.[1, 3]i[6, 7, 8]

Contraindications and cautions#

A known reaction to a product constituent is a reason to avoid that trigger. Itchy, blistered, cracked or persistently inflamed skin requires assessment rather than an assumption that a different acid family will be tolerated. A history of sensitivity is relevant even when a manufacturer’s product description emphasises gentleness.[1, 3, 6]i

Product concentration, pH, vehicle and other actives all affect interpretation of tolerability. Evidence for a particular emulsion cannot simply be transferred to a concentrated peel or a mixture of exfoliating products. Any use around an existing procedure belongs within that procedure’s assessed care plan.[1, 3]i

Clinical uses and the evidence behind them#

Hydration and skin-surface pH

In 16 healthy women, a small split-face study assessed three treatments with 10% and 30% gluconolactone solutions. Corneometer readings on the forehead, periocular skin and cheeks increased through the assessment one week after the last treatment. Both sides received active treatment; this is evidence for a short-term hydration response, not a large vehicle-controlled trial. The authors declared no interests; separate funding was not visible in the retrieved publisher page.[2]

A separate study examined a 10% lactobionic-acid emulsion using sugar-derived emulsifiers. Human skin-surface pH fell at one hour; measurements following 24-hour occlusive exposure supported short-term tolerability. Laboratory cytotoxicity testing was a separate part of the paper. The accessible abstract does not state participant number or body site, so it cannot establish a facial or disease-specific result. Funding details were not retrieved.[3]

Acne and visible ageing concerns

A 1992 double-blind study included 150 patients with mild-to-moderate acne, comparing 14% gluconolactone lotion, vehicle and 5% benzoyl peroxide lotion. Its abstract reports lesion reduction with both actives and fewer side effects with gluconolactone. Treatment duration, body site and sponsor were not established from the retrieved abstract, limiting the detail that can responsibly be carried into practice.[4]

For cosmetic ageing concerns, PHAs have a history of use in surface-smoothing and moisturising products. The broader review literature supports that role, but heterogeneous formulations and methods make it inappropriate to attach one numerical effect to the whole family.[1]

Selecting polyhydroxy acids#

Selection starts with the intended endpoint: moisture, surface roughness or an adjunctive role in an established care plan. Relevant information includes the named acid, its concentration, the finished product’s pH and vehicle, other active ingredients, and whether testing involved that product or only its raw ingredient.[1, 3]i

For dryness, hydration measurements can be relevant; for a claim about barrier function, the endpoints need to address barrier function. TEWL explains water-loss testing, while stratum corneum explains the surface structure. Product selection should not require visible irritation as evidence that a formulation is working.[2, 3]i[1, 3, 6]i

Adverse effects and their management#

Irritant and allergic reactions are possible considerations with cosmetic products. Stinging or discomfort should be assessed in context, particularly when accompanied by an itchy, cracked, blistered or persistent eruption. Identifying and avoiding the responsible exposure is the core principle in contact dermatitis; suspected reactions are not an invitation to keep escalating exfoliation.[6, 7, 8]

Persistent, recurrent or severe symptoms warrant medical assessment. The full ingredient list and exposure history can assist evaluation, because the acid is not necessarily the sole cause. The safety of a previously studied formulation does not diagnose the cause of a new reaction.[1, 3, 6]i

Referral and scope boundaries#

Cosmetic consultation can recognise when a concern needs medical assessment without assigning a disease diagnosis. Moderate/severe acne, nodules or cysts, inadequate response to initial treatment or major distress merit the appropriate medical route. Unresolved dermatitis and new or changing pigmented lesions likewise take precedence over cosmetic exfoliation.[6, 7, 8]

Photoprotection remains part of routine skin-health advice: shade, clothing and a labelled sunscreen have roles that a PHA product does not replace. See sunscreen and SPF for the specific protection framework.[5, 8]i

Mechanism of action#

The class combines hydroxy-acid effects on surface-cell cohesion with water-binding properties. These offer a rationale for smoother-feeling, more hydrated skin. Multiple hydroxyl groups and metal-binding activity also underpin experimental antioxidant interest, but biological effects depend on the particular molecule and formulation.[1]

Human pH measurements provide direct evidence that a selected lactobionic emulsion can acidify the surface. They do not resolve every downstream enzyme or lipid-processing effect in living facial skin. The skin pH and acid mantle entry covers that wider physiology.[3]

Commonly misstated claims#

“Gluconolactone gives 50% sun protection”

Claim heard: A quoted percentage describes sunscreen-like protection in people.

Literature finding: Bernstein and colleagues measured an elastin-promoter response in an in-vitro transgenic photoageing model. Its species and cell type are not specified in the retrieved primary abstract; this result should not be read as a human clinical finding. A separate human experiment concerned sunburn cells, not an SPF determination. Commercial laboratory affiliations are listed in the official record; full funding was not retrieved.[5]i

Supported statement: The percentage belongs to an experimental endpoint, not a human sun-protection factor.

“A higher PHA percentage necessarily moisturises more”

Claim heard: The number on the bottle predicts a proportional hydration benefit.

Literature finding: The small gluconolactone comparison did not find a significant hydration difference between its two tested strengths. That is neither a universal dose-response rule nor proof of equivalence.[2]i

Supported statement: Concentration alone does not predict the moisturising outcome of the complete product.

“A moisture reading proves barrier repair”

Claim heard: Increased corneometer values directly establish recovery of an impaired barrier.

Literature finding: The gluconolactone study assessed hydration; the lactobionic study separately assessed hydration, water loss and erythema. These are distinct measurements.[2, 3]i

Supported statement: A hydration result supports a hydration claim; clinical barrier repair requires appropriate additional evidence.

Areas of remaining uncertainty#

  • Long-term outcomes: Short assessments give limited information about persistence; avoid promising sustained changes from a brief instrumental study.[2, 3]i
  • Disease-specific benefit: The available formulation studies do not settle treatment effectiveness across inflammatory dermatoses; retain the relevant medical pathway.[1, 3, 6]i
  • Transfer between products: Vehicle, pH and mixed actives differ between studies, so match each claim to its formulation rather than rank the family as a whole.[1, 3]i

Frequently asked questions#

Which ingredients count as PHAs in skincare?

Gluconolactone is a common PHA. Lactobionic acid is a related bionic acid commonly included under the same skincare umbrella; the structural distinction is explained above.[1]

Is a PHA product always an exfoliating peel?

No. PHAs also appear in moisturising emulsions. The product’s purpose and formulation determine how its evidence should be interpreted.[1, 3]i

What outcome should a consultation focus on?

The specific concern: for example, moisture or surface texture. An active eruption needs its own assessment rather than being relabelled as a need for stronger exfoliation.[1, 3, 6]i

References#

Each source is graded by evidence tier. Tier 4 material (manufacturer documents, expert consensus, practitioner experience) is useful for protocol and context, and is never presented as equivalent to independent clinical evidence.

  1. Kornhauser A, Coelho SG, Hearing VJ. Applications of hydroxy acids: classification, mechanisms, and photoactivity. Clinical, Cosmetic and Investigational Dermatology. 2010;3:135–142. doi:10.2147/CCID.S9042. PMID:21437068.Tier 4Supports: Hydroxy-acid classification, PHA/bionic-acid distinction, humectant and exfoliative roles, and importance of concentration, pH, vehicle and experimental model. Narrative review, not systematic evidence grading.Funding / interest: Supported in part by the US National Cancer Institute intramural programme. Authors reported no conflicts; one author was retired from FDA and two were NIH-affiliated.
  2. Jarząbek-Perz S, Mucha P, Rotsztejn H. Corneometric evaluation of skin moisture after application of 10% and 30% gluconolactone. Skin Research and Technology. 2021;27(5):925–930. doi:10.1111/srt.13044.Tier 3Supports: Split-face study in 16 healthy women: three treatments, hydration readings on forehead, periocular skin and cheeks, last assessment one week after treatment; no significant difference between tested strengths. Abstract-level retrieval.Funding / interest: Authors reported no declarations of interest on the publisher page. Separate funding was not visible in the retrieved page; university affiliation is not treated as proof of funding.
  3. Tasić-Kostov M, Lukić M, Savić S. A 10% Lactobionic acid-containing moisturizer reduces skin surface pH without irritation—An in vivo/in vitro study. Journal of Cosmetic Dermatology. 2019;18(6):1705–1710. doi:10.1111/jocd.12908. PMID:30859734.Tier 3Supports: Human short-term pH and biophysical tolerability assessments of one alkyl-polyglucoside emulsion; separate laboratory cytotoxicity assay. Abstract does not identify sample size or body site.Funding / interest: Authors had Serbian university affiliations. Separate funding and conflicts were not available in the retrieved publisher abstract; independence is not assumed.
  4. Hunt MJ, Barnetson RS. A comparative study of gluconolactone versus benzoyl peroxide in the treatment of acne. Australasian Journal of Dermatology. 1992;33(3):131–134. doi:10.1111/j.1440-0960.1992.tb00100.x. PMID:1303072.Tier 2Supports: Double-blind comparative trial in 150 patients with mild-to-moderate acne: 14% gluconolactone lotion, vehicle and 5% benzoyl peroxide lotion. Abstract reports lesion reductions and fewer side effects with gluconolactone.Funding / interest: PubMed labels non-US-government research support but does not name the sponsor; funding and commercial interests were not established from the retrieved abstract.
  5. Bernstein EF, Brown DB, Schwartz MD, Kaidbey K, Ksenzenko SM. The polyhydroxy acid gluconolactone protects against ultraviolet radiation in an in vitro model of cutaneous photoaging. Dermatologic Surgery. 2004;30(2 Pt 1):189–195; discussion 196. doi:10.1111/j.1524-4725.2004.30060.x. PMID:14756648.In vitroTier 3Supports: The often-quoted up-to-50% protection figure is from an in-vitro transgenic photoageing model; the retrieved primary abstract does not specify its species or cell type. A separate human experiment assessed sunburn cells; these are not SPF measurements.Funding / interest: Retrieved official abstract lists commercial research-laboratory affiliations including DakDak/Charles River and KGL/Ivy. Sponsor and full conflict declaration were not retrieved.
  6. NHS. Contact dermatitis. Reviewed 3 May 2023. Accessed 16 September 2026.Tier 4Supports: Irritant/allergic reactions, avoidance of the trigger, and medical assessment of persistent, recurrent or severe symptoms.Funding / interest: NHS guidance; no product sponsor stated. Displayed next-review date had passed.
  7. NHS. Acne. Reviewed 3 January 2023. Accessed 16 September 2026.Tier 4Supports: Medical referral for moderate/severe acne, nodules/cysts, unsuccessful initial treatment or significant distress.Funding / interest: NHS guidance; no product sponsor stated. Displayed next-review date had passed.
  8. NHS. Sunscreen and sun safety. Reviewed 24 March 2026. Accessed 16 September 2026.Tier 4Supports: Photoprotection through shade, clothing and sunscreen, and assessment of new or changing lesions.Funding / interest: NHS public-health guidance; no product sponsor or page-specific funding statement.