✓ Glycolic acid verified
The Ordinary Glycolic Acid 7% Exfoliating Toner
Glycolic acid: 7%
Glycolic Acid vs Lactic Acid: Same Family, Very Different Results
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Glycolic acid and lactic acid are both alpha hydroxy acids. They both exfoliate. They both brighten. They both show up in "best AHA" product lists. So what's actually different?
It comes down to one thing: molecular size. Glycolic acid is the smallest AHA (76 daltons), so it penetrates the deepest. Lactic acid is slightly larger (90 daltons), so it stays closer to the surface — and hydrates while it exfoliates. That 18% size difference might sound small, but it changes everything about how these two acids feel on your skin, who they work best for, and what results they deliver.
Quick Comparison
| Factor | Glycolic Acid | Lactic Acid |
|---|---|---|
| Source | Sugarcane | Milk (or vegan fermentation) |
| Molecular weight | 76 daltons (smallest AHA) | 90 daltons |
| Penetration depth | Deeper — reaches lower stratum corneum | Shallower — stays near the surface |
| Exfoliation intensity | More aggressive, faster results | Gentler, more gradual results |
| Hydration | Can be drying at higher concentrations | Actively hydrating — part of skin's NMF |
| Best for | Texture, stubborn pigmentation, acne, anti-aging | Dry skin, sensitive skin, gentle brightening, beginners |
| Irritation risk | Higher — stinging, redness, peeling more common | Lower — rarely causes irritation at OTC concentrations |
| Sun sensitivity | Significant increase | Moderate increase |
| OTC concentrations | 5–10% (peels up to 30–70%) | 5–12% (peels up to 50%) |
| Results timeline | Visible in 1-2 weeks | Visible in 2-4 weeks |
What Is Glycolic Acid?
Glycolic acid is an alpha hydroxy acid derived from sugarcane. It has the smallest molecular size of any AHA at 76 daltons, which means it penetrates the skin more deeply and uniformly than its AHA siblings.
It works by dissolving the bonds (called desmosomes) that hold dead skin cells together in the outermost layer of skin. Because it reaches deeper into this layer than other AHAs, it produces more aggressive exfoliation — which translates to faster visible results but also a higher risk of irritation.
Beyond exfoliation, glycolic acid stimulates collagen production and has pH-dependent antibacterial properties against acne-causing bacteria. It's the most researched AHA in dermatology, with decades of clinical data behind it. For a full breakdown of how different concentrations work, see our percentage guide.
What Is Lactic Acid?
Lactic acid is another alpha hydroxy acid, historically derived from milk — Cleopatra's legendary milk baths were, effectively, lactic acid treatments. Modern skincare formulations typically use vegan lactic acid produced through fermentation of corn or beet sugars.
At 90 daltons, lactic acid's molecules are about 18% larger than glycolic acid's. That difference means it doesn't penetrate as deeply, which makes it inherently gentler. But lactic acid has a unique advantage that glycolic acid doesn't: it's a natural component of the skin's own moisture system (the natural moisturizing factor, or NMF). When you apply lactic acid topically, it functions as a humectant — pulling water into the skin — at the same time it exfoliates.
This dual action makes lactic acid the only AHA that actively hydrates while it exfoliates. Glycolic acid can actually deplete skin moisture at higher concentrations. Lactic acid adds to it.
Lactic acid also inhibits tyrosinase, the enzyme responsible for melanin production. This gives it a brightening pathway beyond simple exfoliation, which is particularly valuable for melanin-rich skin tones where aggressive exfoliation (like glycolic acid) can trigger post-inflammatory hyperpigmentation.
When to Use Glycolic Acid Instead of Lactic Acid
Choose glycolic acid when you need deeper, faster results and your skin can handle it:
- Stubborn texture issues — rough, bumpy skin that hasn't responded to gentler exfoliants. Glycolic acid's deeper penetration reaches buildup that lactic acid simply can't access.
- Established hyperpigmentation — if dark spots have been there for months and lighter exfoliants haven't faded them, glycolic acid removes the pigmented cell layers more efficiently.
- Acne and clogged pores — glycolic acid's antibacterial properties give it an edge over lactic acid for acne-prone skin. It clears the dead cell buildup that traps oil and bacteria in pores.
- Anti-aging on resilient skin — for fine lines and wrinkles, glycolic acid's ability to stimulate collagen at deeper levels produces more noticeable firmness improvements. If your skin tolerates it well, it's the more powerful anti-aging AHA.
- You've plateaued with lactic acid — if you've been using lactic acid for months and results have stalled, your skin is ready for the deeper exfoliation glycolic acid provides.
Important: Glycolic acid increases UV sensitivity more than lactic acid does. Daily SPF 30+ is non-negotiable when using glycolic acid products, regardless of concentration.
When to Use Lactic Acid Instead of Glycolic Acid
Choose lactic acid when gentleness and hydration matter more than speed:
- Sensitive or reactive skin — if glycolic acid stings, causes redness, or makes you peel, lactic acid delivers similar exfoliation benefits without the intensity. It's the AHA most commonly recommended by dermatologists for sensitive skin types.
- Dry or dehydrated skin — lactic acid is the only AHA that hydrates while it exfoliates. If your skin feels tight and flaky, glycolic acid will make that worse. Lactic acid actually helps.
- Darker skin tones prone to hyperpigmentation — melanin-rich skin is more susceptible to post-inflammatory hyperpigmentation from irritation. Lactic acid's gentler approach reduces that risk while still providing brightening through tyrosinase inhibition.
- AHA beginners — if you've never used a chemical exfoliant, lactic acid is the safest starting point. Build your skin's tolerance for 2-3 months, then decide whether to graduate to glycolic acid.
- Winter or dry-climate skincare — when humidity is low and skin barriers are already stressed, lactic acid provides exfoliation without stripping the moisture your skin desperately needs.
- Maintaining results between glycolic acid sessions — many people use glycolic acid 2-3 times per week and lactic acid on off-days to keep skin smooth without over-exfoliating.
Can You Use Both Glycolic Acid and Lactic Acid?
Yes, but don't layer them in the same routine. They're both AHAs that exfoliate through the same mechanism — stacking them doubles your exfoliation intensity without doubling your results, while significantly increasing irritation risk.
The smart way to use both:
Alternating Days (Most Common)
Use glycolic acid on 2-3 nights per week for deeper exfoliation. On other evenings, use lactic acid for gentle maintenance and hydration. This gives you the penetration benefits of glycolic acid without the daily wear on your skin barrier.
Zoning (For Combination Skin)
If your T-zone is oily and congested but your cheeks are dry and sensitive, you can use glycolic acid on the oily areas and lactic acid on the drier areas. This is more work, but it addresses different needs on different parts of your face.
Seasonal Rotation
Some people switch entirely based on the season — glycolic acid in spring/summer when skin is oilier and more resilient, lactic acid in fall/winter when it's drier and more sensitive. This is a practical, low-effort approach.
Important: Over-exfoliation symptoms — persistent redness, stinging with every product, or shiny tight-feeling skin — mean you're using too much acid, regardless of which AHA. Scale back to 1-2 times per week and let your barrier recover before increasing frequency.
Products That Combine Both
Some formulas include glycolic and lactic acid together at balanced concentrations. These are fine to use because the manufacturer has calibrated the total acid level and pH for safety. The concern is only with layering separate products that weren't formulated to work together.
Best Glycolic Acid Products to Start With
If you've read this comparison and decided glycolic acid is right for your skin, here are our recommended products — all verified to contain glycolic acid as a primary active ingredient.
The Ordinary's 7% toner is the gold standard starting point for anyone moving from lactic acid to glycolic acid. The 7% concentration is strong enough to produce visible results within 1-2 weeks but won't overwhelm most skin types. Use it 2-3 evenings per week initially, and consider alternating with a lactic acid product on off-nights to maintain hydration. At around $13 for the 8.1 oz bottle, it's also one of the best values in the category.
✓ Glycolic acid verified
Good Molecules Glycolic Exfoliating Toner
Glycolic acid: 3.5%
At 3.5% glycolic acid, Good Molecules bridges the gap between lactic acid gentleness and glycolic acid effectiveness. If you've been using lactic acid and want to step up but aren't ready for 7-10%, this is the transition product. It's also ideal for the alternating-day approach — use this alongside a lactic acid product on different evenings.
✓ Glycolic acid verified
L'Oreal Paris Revitalift 3.5% Pure Glycolic Acid Brightening Cleanser
Glycolic acid: 3.5%
A cleanser is the lowest-commitment way to try glycolic acid. Because you rinse it off, the acid has limited contact time with your skin — making irritation far less likely than leave-on treatments. L'Oréal's 3.5% formula is gentle enough that many people with mildly sensitive skin can use it daily. It's also a smart option if you want to keep using lactic acid as your leave-on treatment while adding glycolic acid in the cleansing step.
The Molecular Size Factor: Why It Matters More Than Concentration
Most comparison articles focus on concentration — "use 10% glycolic acid for stronger results." But the more important variable is molecular size, and here's why.
Glycolic acid at 76 daltons can reach deeper layers of the stratum corneum regardless of concentration. Lactic acid at 90 daltons stays closer to the surface regardless of concentration. A 10% lactic acid product doesn't suddenly penetrate as deep as a 5% glycolic acid product — it just exfoliates a wider area of the surface more thoroughly.
This is why the two acids feel so different on your skin. Glycolic acid stings more because it reaches nerve endings that lactic acid doesn't touch. It produces faster visible results because it's removing cells that lactic acid can't access. And it carries more irritation risk because deeper penetration means more disruption to your skin barrier.
The concentration of each acid matters within its depth range — 10% glycolic acid exfoliates deeper than 5% glycolic acid. But concentration doesn't change the fundamental penetration difference between the two molecules. That's set by their size.
pH also plays a role. Both acids need a low pH (under 4.0) to work effectively. A well-formulated 10% lactic acid product at pH 3.5 can be more potent than a poorly-formulated 5% glycolic acid product at pH 4.5. Always consider concentration, pH, and molecular size together — not just the percentage on the label.
Frequently Asked Questions
Should I use glycolic acid or lactic acid?
It depends on your skin type and concern. Choose glycolic acid if you have resilient or oily skin and want faster results for texture, acne, or stubborn dark spots. Choose lactic acid if you have dry, sensitive, or melanin-rich skin, or if you're new to chemical exfoliation. Lactic acid hydrates while it exfoliates; glycolic acid penetrates deeper but carries more irritation risk.
Which is stronger, 10% lactic acid or 7% glycolic acid?
7% glycolic acid is generally stronger in terms of penetration depth because glycolic acid's smaller molecular size (76 daltons vs 90 daltons) lets it reach deeper layers of skin. A 10% lactic acid product exfoliates more of the surface but doesn't go as deep. That said, a well-formulated 10% lactic acid at a low pH can produce significant results — strength isn't just about depth.
Which is better for KP, lactic acid or glycolic acid?
Both work for keratosis pilaris, but glycolic acid is generally more effective because the keratin plugs in KP are embedded deeper in the follicle. Glycolic acid's smaller molecules reach those plugs more efficiently. However, if glycolic acid irritates your skin, lactic acid at 10-12% still helps smooth KP bumps over time — it just takes longer. See our full KP guide for product recommendations.
Does glycolic acid pull out blackheads?
Glycolic acid helps prevent and reduce blackheads by dissolving the dead cell buildup that traps oil in pores. It doesn't physically pull them out like an extraction, but regular use (2-3 times per week) keeps pores clearer so fewer blackheads form. For existing deep blackheads, pairing glycolic acid with a salicylic acid product on alternate days is more effective, since salicylic acid is oil-soluble and works inside the pore.
Does lactic acid fade dark spots?
Yes. Lactic acid fades dark spots through two mechanisms: it exfoliates pigmented surface cells, and it inhibits tyrosinase, the enzyme that produces melanin. This dual action makes it effective for hyperpigmentation while being gentler than glycolic acid. It's especially well-suited for melanin-rich skin tones where stronger acids risk triggering more pigmentation through irritation.
What's better than glycolic acid?
It depends on what you need. For sensitive skin, lactic acid or mandelic acid (152 daltons, even gentler) are better. For acne inside pores, salicylic acid (a BHA) is better because it's oil-soluble. For anti-aging, retinol targets collagen more directly. For antioxidant protection, vitamin C is better. Glycolic acid is the best AHA for surface resurfacing, but it's not the best at everything.
What should you never mix with glycolic acid?
Avoid using glycolic acid in the same routine as retinol (doubles irritation and over-exfoliation risk), benzoyl peroxide (can deactivate and irritate), or other AHA/BHA exfoliants at high concentrations. Vitamin C can be used in the same regimen but works best separated — vitamin C in the morning, glycolic acid at night.
What cannot be paired with lactic acid?
Lactic acid has the same pairing restrictions as other AHAs. Avoid combining it with retinol in the same session, high-concentration vitamin C (L-ascorbic acid above 15%), benzoyl peroxide, or other strong exfoliants like glycolic acid or salicylic acid. Lactic acid is gentler than glycolic acid, but stacking multiple actives still overwhelms the skin barrier.
What do Koreans use for hyperpigmentation?
Korean skincare tends to favor gentler brightening ingredients over strong acids. Popular K-beauty options include niacinamide (vitamin B3), arbutin (a natural tyrosinase inhibitor), rice extract, licorice root, and vitamin C derivatives like ascorbyl glucoside. These ingredients are often layered in lightweight serums and essences. If you want the exfoliation benefits of an AHA alongside K-beauty brighteners, lactic acid pairs well with niacinamide.
Which is best for hyperpigmentation, glycolic acid or lactic acid?
For surface-level hyperpigmentation on resilient skin, glycolic acid works faster because it penetrates deeper and removes pigmented cells more aggressively. For hyperpigmentation on sensitive or melanin-rich skin, lactic acid is safer — it exfoliates more gently while also inhibiting tyrosinase (the enzyme that produces melanin), giving it a dual brightening pathway. The risk with glycolic acid on darker skin tones is that irritation can trigger new hyperpigmentation, which defeats the purpose.
Is lactic acid safer than glycolic acid?
Yes, for most people. Lactic acid's larger molecular size (90 vs 76 daltons) means it stays closer to the skin surface, causing less disruption to deeper layers. It also actively hydrates through its role in the skin's natural moisturizing factor. Clinical data shows lower rates of irritation, stinging, and redness with lactic acid compared to glycolic acid at equivalent concentrations. That said, 'safer' doesn't mean 'better' — if your skin tolerates glycolic acid well, it produces faster and more dramatic results.
Is lactic acid anti-aging?
Yes. Lactic acid stimulates collagen production and accelerates cell turnover, both of which help reduce fine lines and improve skin firmness over time. A clinical study found that 12% lactic acid applied for 3 months produced measurable increases in skin thickness and collagen content. It's a gentler anti-aging option than glycolic acid — results take longer to appear but come with significantly less irritation risk. For people who can't tolerate retinol or glycolic acid, lactic acid is one of the best evidence-backed anti-aging alternatives.