What is Gluconolactone? The PHA Ingredient Explained

Gluconolactone is the specific form of PHA — Polyhydroxy Acid — used in The INKEY List's exfoliating products. It is the most extensively studied PHA in skincare science, and the most widely used in professional-grade formulations. If you have ever seen "PHA" on a skincare label and wondered what the actual ingredient is, gluconolactone is almost always the answer.

This guide explains exactly what gluconolactone is, how it works in the skin, what makes it different from other exfoliating acids, and why it is the ingredient of choice for sensitive skin, daily exfoliation, and pregnancy-safe skincare. If you want the complete picture on PHA in general — including full routine guidance, product comparisons, and ingredient pairings — our complete PHA ingredient guide covers everything in one place.

What is Gluconolactone?

Gluconolactone is an organic compound derived from gluconic acid — a naturally occurring substance found in honey, fruit, and the human body. In chemistry, it is classified as a polyhydroxy acid (PHA) — a category of exfoliating acids defined by their multiple hydroxyl (-OH) groups and larger molecular size relative to AHAs and BHAs.

In skincare, gluconolactone is used as a multifunctional active ingredient. It delivers three simultaneous actions that no other single exfoliating acid replicates in the same combination:

Exfoliation — loosens and removes dead skin cells at the surface of the stratum corneum
Hydration — functions as a humectant, drawing moisture into the skin's surface layers
Antioxidant protection — neutralises free radical damage from UV exposure, pollution, and environmental stressors

This triple-action profile is what makes gluconolactone the most complete and versatile PHA in skincare formulation — and why it is the specific PHA used in both the PHA Toner (£13) and the PHA Body Water Cream (£13).

How Does Gluconolactone Work in the Skin?

The Exfoliation Mechanism

The skin's outer surface — the stratum corneum — is held together by proteins called desmosomes. These are the biological bonds that keep dead skin cells (corneocytes) in place on the skin's surface. Over time, as the natural process of desquamation slows — due to age, hormonal changes, UV exposure, or environmental stress — dead cells accumulate on the surface. The result is dull, uneven, rough-textured skin.

Gluconolactone's multiple hydroxyl (-OH) groups weaken the bonds between these desmosomes, allowing the dead corneocytes to shed more efficiently and naturally. This is chemical exfoliation — no friction, no mechanical force, no scrubbing. The acid does the work, loosening the dead cells at the surface so they shed the way the skin naturally intends, just more efficiently and consistently.

Because gluconolactone's molecular weight is approximately 178 Da — significantly larger than glycolic acid at 76 Da, and larger than salicylic acid at 138 Da — it cannot penetrate to the deeper layers of the epidermis where most acids trigger irritation. It works exclusively at the outermost surface of the stratum corneum. This is the defining characteristic that makes gluconolactone so well-suited to sensitive skin: effective exfoliation without the depth of penetration that causes redness, stinging, or barrier compromise.

The Humectant Mechanism

Unlike most exfoliating acids, gluconolactone is also a humectant. Humectants are molecules that attract and bind water molecules — drawing moisture from the environment and from the deeper layers of the skin toward the surface.

In practical terms, this means that as gluconolactone exfoliates the skin's surface, it is simultaneously drawing moisture into it. Skin feels more hydrated after use, not less — a fundamental difference from the temporary tightness or dryness that many people experience after using glycolic acid or salicylic acid products.

This dual action — exfoliation and hydration in a single molecule — is what makes gluconolactone uniquely efficient for daily skincare use. Other acids require a separate hydrating step immediately after to compensate for what they strip. Gluconolactone provides both simultaneously.

The Antioxidant Mechanism

Gluconolactone has chelating properties — meaning it binds to metal ions (such as iron and copper) that would otherwise catalyse free radical reactions in the skin. Free radicals are unstable molecules generated by UV exposure, pollution, smoke, and other environmental stressors. They damage skin cells, break down collagen, and accelerate the visible signs of ageing.

By neutralising the metal ions that trigger these reactions, gluconolactone provides a meaningful layer of environmental defence. This does not replace SPF — nothing replaces SPF — but it adds antioxidant activity that most exfoliating acids simply do not deliver. This antioxidant function is unique to PHA and specifically well-documented in gluconolactone research.

Gluconolactone vs Other Exfoliating Acids

Understanding where gluconolactone sits in the landscape of exfoliating acids is essential for understanding why it is used in our formulations rather than alternatives.

Gluconolactone vs Glycolic Acid

Glycolic acid is an Alpha Hydroxy Acid (AHA) with a molecular weight of approximately 76 Da — the smallest AHA and the most deeply penetrating. It is highly effective at brightening and resurfacing skin, but its small size means it reaches the upper dermis, where it regularly causes stinging, redness, peeling, and barrier disruption in sensitive skin types.

Gluconolactone has a molecular weight of approximately 178 Da. It delivers effective exfoliation with a significantly lower irritation risk, can be used daily, and hydrates as it works. The trade-off is that visible brightening results build more gradually — but for sensitive, dry, or reactive skin, this is the appropriate exchange. Learn more in our PHA Toner vs Glycolic Acid Toner comparison guide.

Gluconolactone vs Lactic Acid

Lactic acid is a larger AHA than glycolic acid (molecular weight approximately 90 Da) with some inherent humectant properties — it is gentler than glycolic acid and moderately better tolerated by sensitive skin. However, it still penetrates more deeply than gluconolactone and carries a higher irritation risk for very reactive skin types.

Gluconolactone is gentler than lactic acid, works only at the surface, and delivers stronger humectant action. For the most sensitive skin types, gluconolactone is the more appropriate choice.

Gluconolactone vs Salicylic Acid

Salicylic acid is a Beta Hydroxy Acid (BHA) with a molecular weight of approximately 138 Da. It is oil-soluble, which means it penetrates inside the pore lining — making it highly effective for congested, oily skin. However, it can be significantly over-drying and irritating for dry, sensitive, or reactive skin, and is not recommended during pregnancy.

Gluconolactone is water-soluble and surface-acting. It does not penetrate the pore in the same way, but it effectively removes dead skin cells from the surface of the follicle opening and is safe during pregnancy. For blemish-prone skin that cannot tolerate salicylic acid, the combination of gluconolactone and niacinamide in the PHA Toner addresses oil control and surface congestion in a pregnancy-safe format.

Gluconolactone vs Lactobionic Acid

Lactobionic acid is another PHA, derived from lactose. It has an even larger molecular weight than gluconolactone and is considered ultra-gentle — primarily used in clinical formulations for extremely reactive or compromised skin. Its hydrating and barrier-supporting properties are excellent, but it is less widely available in mass-market skincare and has less clinical research behind it for general skincare use than gluconolactone.

Gluconolactone is the more extensively researched and more widely formulated PHA, with a stronger evidence base for its exfoliating, humectant, and antioxidant actions. It remains the gold standard PHA for effective, science-backed skincare.

Why Gluconolactone Is Used in Our Formulas

The Concentration: Why 3%?

Both the PHA Toner and the PHA Body Water Cream are formulated with 3% gluconolactone. This is not an arbitrary figure — it is the concentration at which gluconolactone consistently delivers clinically meaningful exfoliation while maintaining the low irritation profile that defines PHA as a category.

Higher concentrations of AHAs — 10% glycolic acid, for example — require careful cycling, gradual introduction, and are not appropriate for daily use in most skin types. At 3%, gluconolactone can be built up to daily use in both AM and PM routines once the skin has adjusted, without the barrier disruption risks associated with higher-concentration acid formulations.

The pH: Why 3.62?

Exfoliating acids are only active within an acidic pH range. The PHA Toner is formulated at pH 3.62 — precisely calibrated to keep the gluconolactone active and effective while remaining within a range that the skin can tolerate comfortably, even with daily use.

At pH values above approximately 4.0, many exfoliating acids begin to lose their activity. At pH values significantly below 3.0, irritation risk increases substantially. pH 3.62 sits in the optimal window for PHA exfoliation — effective, stable, and skin-compatible for consistent use.

Why Gluconolactone Specifically?

Of the three main PHAs used in skincare — gluconolactone, lactobionic acid, and galactose — gluconolactone is the one with the broadest and deepest clinical evidence base. It is the most studied, the most widely formulated, and the most comprehensively documented for the three actions it delivers: exfoliation, humectant hydration, and antioxidant protection.

It is also the most versatile in formulation — it works effectively in both lightweight toner formats (the PHA Toner) and richer leave-on body cream formats (the PHA Body Water Cream), maintaining its activity across different textures and vehicles.

Gluconolactone in The INKEY List Products

PHA Toner (£13 / 100ml) — 3% Gluconolactone + 3% Niacinamide

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4.4 stars from 332 verified reviews
Confirmed safe during pregnancy and breastfeeding

The PHA Toner (£13) combines 3% gluconolactone with 3% Niacinamide in a lightweight, leave-on toner format. The gluconolactone handles exfoliation and hydration simultaneously. The Niacinamide delivers oil control, pore minimisation, and additional anti-inflammatory support.

The combination is specifically designed to make exfoliation and oil management happen in a single, efficient step — removing the need for a separate exfoliant and a separate oil-control product in the same routine.

Key formulation details:

3% Gluconolactone — exfoliation, humectant hydration, antioxidant protection
3% Niacinamide — oil control, pore minimisation, brightening
Aloe Vera — calming and soothing
pH 3.62 — calibrated for effective, daily-use PHA exfoliation
Alcohol-free, fragrance-free, gluten-free

Suitable for: All skin types, sensitive skin, oily skin, blemish-prone skin, pregnancy and breastfeeding
How to use: Apply to a cotton pad after cleansing, sweep over face and neck. No rinsing. AM and/or PM. Start at 2–3x per week and build to daily use.

PHA Body Water Cream (£13 / 150ml) — 3% Gluconolactone + Jojoba + Rice Bran

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4.5 stars from 286 verified reviews
Confirmed safe during pregnancy and breastfeeding

The PHA Body Water Cream (£13) uses the same 3% gluconolactone active in a richer leave-on body cream format, paired with Jojoba and Rice Bran for additional softening and nourishing action on body skin.

The gluconolactone works identically on body skin as it does on facial skin — loosening and removing dead skin cells at the surface while drawing moisture in. The body cream format allows the ingredient to remain in sustained contact with the skin, delivering its full triple action without rinsing.

Key formulation details:

3% Gluconolactone — exfoliation, humectant hydration, antioxidant protection
Jojoba — emollient softening and sustained hydration
Rice Bran — nourishing, skin tone-evening support
Alcohol-free, fragrance-free, silicone-free

Clinical results (4-week trial, 21 participants):

Clinically proven to reveal brighter, smoother, and more even body skin in just 1 week*
Clinically proven to strengthen the skin barrier and significantly improve and maintain hydration*
Clinically proven to visibly reduce dry, flaky body skin in just 7 days*
97% of users said it was gentle enough for daily use*

Suitable for: All skin types, sensitive skin, keratosis pilaris, pregnancy and breastfeeding
How to use: Apply AM and/or PM to clean, dry body skin. Massage until fully absorbed. No rinsing required.

What Makes Gluconolactone Different: The Key Properties Summarised

It Has the Largest Molecule of the Common Exfoliating Acids

At approximately 178 Da, gluconolactone's molecular weight is more than double that of glycolic acid (76 Da) and larger than salicylic acid (138 Da) and lactic acid (90 Da). Size determines penetration depth — and penetration depth determines irritation risk. Gluconolactone's size is what makes it the gentlest and most broadly tolerated exfoliating acid available.

It Is the Only Common Exfoliating Acid That Also Hydrates

Glycolic acid does not hydrate. Salicylic acid does not hydrate. Lactic acid has some humectant properties but they are secondary to its exfoliating function and not as well-documented as gluconolactone's. Gluconolactone's humectant action is a primary, well-established function of the molecule — not a secondary effect.

It Is One of the Only Exfoliating Acids With Antioxidant Properties

The chelating and free radical-neutralising properties of gluconolactone are unique among mainstream exfoliating acids. Most AHAs and BHAs are purely exfoliating — they do not provide any antioxidant benefit. Gluconolactone delivers exfoliation, hydration, and environmental protection in a single ingredient.

It Is Confirmed Safe During Pregnancy and Breastfeeding

Retinol, salicylic acid in leave-on formats, and high-concentration AHAs all carry pregnancy cautions. Gluconolactone — due to its large molecular size and inability to penetrate systemically — carries none of these cautions. It is one of very few exfoliating actives confirmed safe throughout pregnancy and breastfeeding. Read our complete guide to skincare safety during pregnancy for the full breakdown.

It Is Suitable for Daily Use

Most exfoliating acids require cycling — rest days, limited weekly frequency, careful monitoring. Gluconolactone at 3% in a leave-on format is gentle enough to build to daily use in both AM and PM routines, without the barrier disruption risks that cycling protocols exist to prevent.

How to Use Gluconolactone in Your Skincare Routine

Face Routine with Gluconolactone (PHA Toner)

Morning:

Cleanse — gently remove overnight products
PHA Toner — apply to cotton pad, sweep over face and neck. No rinse.
Hyaluronic Acid Serum (£16) — apply to slightly damp skin after toning
Eye treatment if using
Moisturiser
SPF — essential in the morning when using any exfoliant

Evening:

Double cleanse — Oat Cleansing Balm (£15) to remove SPF and makeup, then your regular cleanser
PHA Toner — same method as morning
Treatment serum (not Retinol or Vitamin C in the same step)
Moisturiser

Body Routine with Gluconolactone (PHA Body Water Cream)

Shower or bathe — cleanse body skin thoroughly
Pat dry — do not rub
PHA Body Water Cream — apply to clean, dry skin and massage until fully absorbed. No rinsing. No separate moisturiser needed.
SPF (morning only) — on any body skin exposed to the sun

What to Use Gluconolactone With

Highly recommended pairings:

Gluconolactone + Hyaluronic Acid — exfoliation followed immediately by deep humectant hydration. One of the most effective pairings in skincare.
Gluconolactone + Niacinamide — already combined in the PHA Toner. Oil control and exfoliation in one step.
Gluconolactone + SPF — essential in the morning. Any exfoliant increases UV sensitivity.

Use separately:

Gluconolactone + Retinol — effective ingredients individually, but use in separate routines (PHA morning, Retinol evening). Read our guide on what not to mix with Retinol.
Gluconolactone + Vitamin C — use at different times of day

Avoid:

Gluconolactone + other exfoliating acids in the same routine — do not layer AHAs or BHAs with gluconolactone in the same step. Read our complete guide to using acids in your skincare routine.

How to Introduce Gluconolactone Into Your Routine

Even though gluconolactone is the gentlest exfoliating acid available, it is a new active ingredient for your skin — and all new actives should be introduced gradually.

Week 1–2: 2–3 times per week, evening only. Allow skin to adjust between sessions. Do not introduce any other new product simultaneously.

Week 3–4: Increase to 3–4 times per week. Begin morning use if desired, always followed by SPF.

Week 5 onwards: Daily use once skin has fully adjusted, AM and/or PM.

Always patch test before first use. Apply a small amount to the inner arm and wait 24 hours before applying to the face or body. Read our complete patch testing guide for the full method.

Frequently Asked Questions

What is gluconolactone?
Gluconolactone is a Polyhydroxy Acid (PHA) derived from gluconic acid — a naturally occurring substance found in honey, fruit, and the human body. In skincare, it is used as a multifunctional active that exfoliates, hydrates, and protects skin against environmental damage simultaneously. It is the specific PHA used in The INKEY List's PHA Toner (£13) and PHA Body Water Cream (£13).

Is gluconolactone the same as PHA?
PHA is the category — Polyhydroxy Acid. Gluconolactone is the most common and most studied specific PHA used in skincare. Other PHAs include lactobionic acid and galactose, but gluconolactone is the gold standard for effective, daily-use PHA exfoliation.

Is gluconolactone safe for sensitive skin?
Yes — gluconolactone is the most broadly appropriate exfoliating acid for sensitive skin. Its large molecular size means it works only at the skin's surface, without penetrating to the deeper layers where irritation is triggered. It also has mild anti-inflammatory properties and draws moisture into the skin as it exfoliates, making it uniquely well-suited to sensitive and reactive skin types.

Is gluconolactone safe during pregnancy?
Yes. Gluconolactone is confirmed safe during pregnancy and breastfeeding. Its large molecular size prevents systemic absorption — which is the primary concern with skincare ingredients during pregnancy. Both INKEY PHA products containing gluconolactone are explicitly confirmed pregnancy-safe.

How does gluconolactone compare to glycolic acid?
Glycolic acid has a significantly smaller molecular weight (76 Da vs gluconolactone's 178 Da), which means it penetrates more deeply and delivers faster, more dramatic brightening results — but with a considerably higher irritation risk. Gluconolactone delivers effective surface exfoliation with dramatically lower irritation risk, plus the additional benefits of humectant hydration and antioxidant protection that glycolic acid does not provide. For sensitive skin, gluconolactone is the more effective choice overall — because glycolic acid's irritation negates its own benefits in reactive skin types. Read the full comparison in our PHA Toner vs Glycolic Acid Toner guide.

Can gluconolactone be used every day?
Yes — once skin has adjusted. Start at 2–3 times per week and build gradually to daily use. The 3% concentration in both INKEY PHA products is formulated specifically for daily use once the skin has adapted.

Does gluconolactone cause purging?
The risk of purging with gluconolactone is minimal to non-existent. Because it works only at the skin's surface and does not penetrate to the follicle depth where purging originates, the adjustment period is significantly milder than with AHAs or BHAs.

What is the difference between gluconolactone and lactobionic acid?
Both are PHAs, but gluconolactone is more extensively studied and more widely formulated in mainstream skincare. Lactobionic acid has an even larger molecular weight and is considered ultra-gentle — primarily used in clinical formulations for very reactive or compromised skin. Gluconolactone delivers a better balance of documented exfoliation efficacy and gentleness for general skincare use.

Does gluconolactone help with keratosis pilaris?
Yes — consistent use of gluconolactone on KP-affected areas (typically the upper arms and thighs) gradually loosens the keratin build-up blocking the hair follicle opening, improving the texture and appearance of the bumps over time. The PHA Body Water Cream is specifically appropriate for KP management — applied daily to affected areas, with visible improvement typically appearing at the 8–12 week mark. Read our complete guide to body exfoliation for more detail.

The Bottom Line

Gluconolactone is not just another exfoliating acid — it is the most complete exfoliating acid. It exfoliates, hydrates, and protects simultaneously. It is suitable for all skin types including the most sensitive. It can be used daily. It is safe during pregnancy. And it delivers cumulative, sustained results without the irritation risk that makes stronger acids unsuitable for a large proportion of skincare users.

The PHA Toner (£13) and the PHA Body Water Cream (£13) are the two most accessible, best-formulated ways to incorporate gluconolactone into a daily skincare routine — face and body — from a single, well-understood active at a clinically supported concentration.

For the complete guide to PHA — including full routine building, ingredient pairings, and the science behind how gluconolactone works — read our complete PHA ingredient guide.

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