# PHAs (Polyhydroxy Acids): The Exfoliant for Sensitive Skin > PHAs are large-molecule exfoliants that work only at the skin surface. *Polyhydroxy acids (PHAs) are a newer generation of hydroxy acids — including gluconolactone, lactobionic acid, and galactose — with larger molecular weights (178–194 g/mol) than AHAs, confining their action to the outermost stratum corneum. This surface-limited penetration means they exfoliate without the irritation, stinging, or photosensitivity associated with glycolic or lactic acid.* - Canonical: https://beautycomparison.com/pha-guide - Reviewed: 2026-06-20 - Publisher: Beauty Comparison (Beauty Comparison Editorial) — independent, brand-neutral ## Key takeaways - PHAs (gluconolactone, lactobionic acid, galactose) have molecular weights of 178–194 g/mol — two to three times larger than glycolic acid — confining their exfoliating action to the skin surface only. - Clinical studies show a PHA skincare regimen delivers antiaging benefits statistically comparable to an AHA regimen, with significantly superior tolerability. - PHAs provide unique benefits no AHA offers: antioxidant chelation of metal ions that catalyze free-radical damage, and meaningful UV-protective effects at the stratum corneum level. - Gluconolactone at 14% outperformed 5% benzoyl peroxide for acne reduction in one trial while causing less irritation — making it a compelling sensitive-skin acne option. - PHAs do not significantly increase photosensitivity, unlike AHAs — though daily SPF remains best practice for anyone using any exfoliant. - Suitable for rosacea, eczema-prone, barrier-compromised, post-procedure, and pregnant individuals who cannot use conventional AHAs. ## What Are PHAs? Polyhydroxy acids (PHAs) are a third generation of hydroxy acids, developed after alpha-hydroxy acids (AHAs) and beta-hydroxy acids (BHAs) to address the tolerability problems of both. The primary PHAs used in skincare are: - **Gluconolactone** (the most widely studied PHA) — derived from glucose - **Lactobionic acid** — derived from lactose, a disaccharide - **Galactose** — a monosaccharide with mild hydroxy acid activity All are significantly larger molecules than conventional AHAs. Gluconolactone at 178 g/mol and lactobionic acid at 358 g/mol compare to [glycolic acid](/glycolic-acid-guide) at 76 g/mol and lactic acid at 90 g/mol. That size difference is the key to understanding PHAs. ### Why Size Matters Molecular size determines how far a hydroxy acid penetrates the skin. Glycolic acid's small size allows it to penetrate deep into the epidermis and produce the potent effects — and the irritation — associated with glycolic products. PHAs, by contrast, are confined to the outermost stratum corneum. They exfoliate there, providing the surface-smoothing, brightening, and hydration benefits of AHAs, but they do not penetrate far enough to cause the stinging, erythema, or photosensitivity that sensitive skin types cannot tolerate. This is not a compromise — it is a different mechanism tailored to a specific need. For someone with rosacea, reactive skin, or recovering from a procedure, the gentleness of PHAs is not a weakness; it is the point. --- ## How PHAs Work ### Exfoliation PHAs lower local pH at the skin surface, interfering with corneodesmosomes (the protein bridges between dead corneocytes) and promoting their shedding. The result is smoother surface texture, reduced dullness, and improved tone — delivered without the concentrated acid exposure that irritates sensitive skin. ### Antioxidant Activity PHAs are metal-ion chelators. Free radical damage — a key driver of photoaging and UV-induced skin damage — is catalyzed by transition metal ions (especially copper and iron) present in skin. PHAs bind and sequester these ions, interrupting the catalytic cycle and reducing oxidative stress. This antioxidant mechanism is not shared by AHAs and represents a meaningful additional benefit for anti-aging use. ### UV Protection at the Surface Level A well-designed *in vitro* study (Bernstein 2004) found that gluconolactone provided up to 50% protection against UV-induced DNA damage at the surface of the stratum corneum and did not increase sunburn cell formation — an effect not seen with glycolic acid. This does not replace SPF (PHAs are not sunscreen ingredients), but it represents an additional layer of protection beyond their exfoliating action. ### Humectant Function Like lactic acid, PHAs attract water into the stratum corneum and reduce transepidermal water loss (TEWL). Products containing PHAs therefore support hydration as they exfoliate — an important consideration for dry and sensitive skin types where conventional exfoliants often worsen dryness. ### Barrier Strengthening PHAs improve the skin's protective barrier function by reinforcing the stratum corneum's structural integrity. Unlike AHAs, which transiently thin and disrupt the surface barrier during exfoliation, PHAs appear to strengthen and seal the barrier — reducing TEWL and improving the skin's resistance to external irritants. A study on gluconolactone-based lotion confirmed this barrier-strengthening mechanism. --- ## PHA Benefits: What the Evidence Shows ### Anti-Aging A key clinical study directly comparing a PHA skincare regimen to an AHA regimen found that both produced statistically significant anti-aging benefits — with equivalent improvements in fine lines, skin texture, and tone — but the PHA regimen was significantly better tolerated. For skin that cannot sustain an AHA regimen long-term due to irritation, PHAs deliver comparable outcomes with dramatically better adherence. ### Sensitive and Rosacea-Prone Skin Rosacea patients are commonly told to avoid all exfoliants. PHAs provide an evidence-based exception: their surface-limited action, barrier-strengthening effect, and anti-inflammatory properties make them suitable for rosacea skin in a way that glycolic or lactic acid are not. ### Acne-Prone Skin A clinical trial found 14% gluconolactone lotion reduced acne lesions more effectively than 5% benzoyl peroxide while causing significantly less irritation. For acne-prone, sensitive, or rosacea-acne overlap presentations, this is clinically meaningful: effective acne reduction without the barrier disruption of conventional treatments. ### Post-Procedure Skin After laser resurfacing, chemical peels, or microdermabrasion, the skin barrier is temporarily compromised and cannot tolerate conventional AHAs. PHAs are appropriate for maintaining exfoliation continuity during the recovery phase, when other exfoliants cannot be used. ### Eczema-Prone and Atopic Skin The barrier-strengthening, moisturizing, and anti-inflammatory properties of PHAs make them usable in eczema-prone skin (between flares), where AHAs would likely exacerbate barrier dysfunction. --- ## PHAs vs. AHAs: Head-to-Head | | AHAs (Glycolic/Lactic) | PHAs (Gluconolactone) | |---|---|---| | Molecular weight | 76–90 g/mol | 178–358 g/mol | | Penetration depth | Moderate to deep epidermis | Surface stratum corneum only | | Exfoliation strength | Moderate to strong | Mild to moderate | | Antioxidant effect | Minimal | Yes — metal-ion chelation | | UV protection | None (increases photosensitivity) | Modest UV-protective effect | | Humectant | Lactic acid only | Yes | | Barrier effect | Transiently disrupts | Strengthens | | Suitable for sensitive skin | With care | Yes | | Suitable for rosacea | Generally not | Yes | | Photosensitivity | Increased | Minimal | If irritation or barrier disruption is not a concern and maximum exfoliation efficacy is the goal, [glycolic acid](/glycolic-acid-guide) or [lactic acid](/lactic-acid-guide) are stronger choices. For anyone with reactive, sensitive, or compromised skin — or anyone who has had a poor experience with AHAs — PHAs are the definitive better option. --- ## Common PHAs in Skincare Products ### Gluconolactone The most widely studied PHA. Used in both leave-on products (serums, toners, moisturizers) and rinse-off products (cleansers). Effective concentrations: 5–14%. The 14% concentration in the acne-versus-benzoyl-peroxide trial is well above what most retail products contain; most OTC gluconolactone products are formulated at 5–8%. ### Lactobionic Acid A disaccharide PHA (much larger than gluconolactone). Even more superficial action, stronger humectant effect. Found in moisturizers and serums marketed for very sensitive or mature skin. Provides meaningful hydration alongside gentle surface smoothing. ### Galactose Less studied than gluconolactone or lactobionic acid. Sometimes combined with other PHAs or AHAs in multi-acid formulations. --- ## How to Use PHAs PHAs are genuinely forgiving compared to conventional AHAs, but the following still applies: 1. **Apply to clean, dry skin** in the evening. Although PHAs have lower photosensitivity implications than AHAs, evening use is still the standard for any exfoliating acid. 2. **No ramp-up protocol required for most people** — unlike glycolic acid, PHAs can often be used nightly from the start in sensitive skin. If you have extremely reactive skin, begin 3 nights per week. 3. **Follow with moisturizer.** PHAs work with your moisturizer, not against it — their humectant effect is enhanced by sealing with an occlusive or emollient layer. 4. **Apply SPF 30+ every morning.** While PHAs do not significantly increase photosensitivity, this is best practice for all skincare actives and prevents undoing texture and tone gains. 5. **PHAs can be layered with** niacinamide, ceramides, hyaluronic acid, and most barrier-support ingredients without concern. 6. **PHAs with retinol:** PHAs are one of the few exfoliants gentle enough to consider using on the same nights as low-concentration retinol, though alternate-night use is still the safer default for beginners. ### What Not to Combine on the Same Night - **Glycolic or lactic acid at standard concentrations** — adding a strong AHA removes the tolerability advantage of choosing a PHA. - **High-strength vitamin C (L-ascorbic acid at pH ≤3.5)** — potential pH competition; vitamin C is better used in the morning. --- ## Who Should Use PHAs PHAs are suitable for anyone, but they are the *first-choice* exfoliant for: - **Rosacea or rosacea-prone skin** - **Eczema or atopic dermatitis (between flares)** - **Post-procedure recovery** (after peels, lasers, microneedling) - **Sensitive skin that has had poor reactions to AHAs** - **Pregnant individuals** who want to continue gentle exfoliation (PHAs are generally considered compatible with pregnancy at normal skincare concentrations) - **Very dry or barrier-compromised skin** where AHA exfoliation would worsen dryness For everyone else, PHAs are a valid and pleasant choice — just with the understanding that the results will be more gradual than with AHAs. ## FAQ **What does current evidence say about PHAs in 2026?** PHAs remain well supported by the evidence accumulated since the late 1990s. Key findings are stable: a PHA regimen produces statistically significant anti-aging benefits comparable to AHA regimens with meaningfully better tolerability; gluconolactone provides antioxidant and UV-protective effects not seen with AHAs; PHAs strengthen rather than disrupt the skin barrier. A 2023 PMC study on gluconolactone-based lotion confirmed biological safety and skin activity in a dermocosmetic application. No downgrade in evidence has occurred; PHAs continue to be recommended as the preferred exfoliant for sensitive, rosacea, and barrier-compromised skin. **Are PHAs better than AHAs?** For sensitive, reactive, rosacea, or barrier-compromised skin: yes, PHAs are the better choice. For skin that tolerates exfoliants well and wants maximum efficacy: AHAs (particularly glycolic acid) deliver faster, stronger results. PHAs are not a compromise — they are the right tool for the right skin type. The two categories complement each other in that PHAs allow anyone who cannot tolerate AHAs to still benefit from chemical exfoliation. **Can I use PHAs if I have rosacea?** Yes — PHAs are one of the few exfoliants generally considered compatible with rosacea. Their surface-limited action, barrier-strengthening properties, and anti-inflammatory characteristics make them a reasonable choice for rosacea skin, whereas glycolic and lactic acid can exacerbate flushing and barrier disruption. Start with a low concentration and a single application per week; monitor for any increase in redness or flushing, and discuss with a dermatologist if you have any uncertainty. **Do PHAs increase sun sensitivity?** Minimally to not at all — which is one of their advantages over AHAs. An in vitro study found gluconolactone actually provides modest UV protection at the skin surface rather than increasing sensitivity. However, daily SPF 30+ remains best practice for anyone using any skincare acid, as sun protection is fundamental to preserving the results of exfoliation. **What percentage of PHA should I look for in a product?** Most OTC PHA products use gluconolactone at 5–8%. The 14% concentration used in the acne study is higher than most retail formulations. For gentle daily exfoliation and hydration, 5–8% is effective and appropriate. For more active skin concerns in sensitive skin (acne, mild photoaging), look for formulations in the 8–10% range if available. pH matters: effective PHAs should be formulated at pH 3.5–4.5. ## Sources - A polyhydroxy acid skin care regimen provides antiaging effects comparable to an alpha-hydroxyacid regimen — PubMed / Cutis (2004-02-01): https://pubmed.ncbi.nlm.nih.gov/15002657/ - The polyhydroxy acid gluconolactone protects against ultraviolet radiation in an in vitro model of cutaneous photoaging — PubMed / Dermatologic Surgery (2004-02-01): https://pubmed.ncbi.nlm.nih.gov/14756648/ - Efficacy and safety of a new peeling formulated with a pool of PHAs for the treatment of all skin types, even sensitive — PubMed Central / Cosmetics (2023-03-27): https://pmc.ncbi.nlm.nih.gov/articles/PMC10087944/ - Investigation on the Biological Safety and Activity of a Gluconolactone-Based Lotion for Dermocosmetic Application — PubMed Central / Cosmetics (2023-05-01): https://pmc.ncbi.nlm.nih.gov/articles/PMC10221517/ - Effects of Cosmetic Formulations Containing Hydroxyacids on Sun-Exposed Skin: Current Applications and Future Developments — PubMed Central / Dermatology Research and Practice (2012-05-03): https://pmc.ncbi.nlm.nih.gov/articles/PMC3362829/