Lactic Acid for Skin: What It Does That Glycolic Acid Does Not

Lactic acid is an alpha hydroxy acid that exfoliates by loosening the bonds holding dead cells to the skin surface, and unlike glycolic acid it also holds water in the skin. As sodium lactate it is a known component of the skin's own natural moisturising complex, which is why it is described in the dermatological literature as an excellent moisturiser. That dual role, exfoliant and humectant in the same molecule, is the difference that matters when you are choosing between lactic acid and glycolic acid for Indian skin.

Both lactic acid and glycolic acid are alpha hydroxy acids and both work by lowering pH at the skin surface, which dissolves the desmosomes holding dead cells together. Lactic acid is the larger of the two molecules, so it penetrates more slowly and more superficially. It is also the only common AHA that is already part of the skin's moisturising system. Concentration decides everything: research published in Molecules found that 1% AHA alters the pH of only the outer three layers of the stratum corneum, while 10% affects all ten to twenty layers. For melanin-rich skin, the gentler acid used consistently beats the stronger acid used carelessly, because irritation here becomes pigmentation.

What Does Lactic Acid Do for Skin?

Alpha hydroxy acids are organic acids carrying one hydroxyl group at the alpha position. The group includes glycolic acid, lactic acid, malic acid, tartaric acid and citric acid, and a 2018 review published in Molecules by Tang and Yang describes them as naturally occurring organic acids present in many foods and milk sugars.

The mechanism is physical chemistry rather than biology. According to that review, the acidic nature of AHAs reduces pH in the epidermis, inhibits transferases and kinases, and interferes with the formation of ionic bonds. All three effects contribute to desmosome resolution, meaning the protein rivets holding dead cells to each other come apart, which stimulates desquamation.

Lactic acid does not scrub anything off. It unsticks cells that were already due to leave. That distinction is the reason a well-formulated acid is gentler on Indian skin than a walnut scrub, even though the acid sounds more aggressive.

The One Thing Lactic Acid Does That Glycolic Acid Does Not

Every AHA exfoliates. Only one of them is already in your skin.

Tang and Yang state it directly: lactic acid, as sodium lactate, is a well-known part of the skin's natural moisturising complex and is considered an excellent moisturiser. Glycolic acid has no equivalent role. It exfoliates, and that is the extent of what it does at the surface.

This is why lactic acid tends to leave skin feeling softer after use while glycolic acid tends to leave it feeling tighter. The acid is doing two jobs at once: opening up the surface and holding water in it. For dry, sensitised or barrier-compromised skin, which describes a large share of the people who abandon acids after one bad week, that second job is what makes the first one survivable.

Lactic acid is also the larger of the two molecules, which slows its penetration and keeps its action more superficial than glycolic acid's. Be careful what you read on this point: ingredient blogs quote lactic acid's molecular weight as both 90 and 118, and only one of those can be right. Lactic acid is C₃H₆O₃, which puts it at roughly 90 g/mol against glycolic acid's C₂H₄O₃ at roughly 76. The direction is what matters. Lactic acid is bigger, and bigger goes in slower.

Lactic Acid vs Glycolic Acid, Side by Side

Neither is the better acid in the abstract. Glycolic acid going deeper is an advantage if your skin tolerates it and a liability if it does not, and in melanin-rich skin the liability is not just discomfort.

Concentration is the Entire Argument

Most arguments about which acid is better are actually arguments about dose, and the Molecules review has a figure that settles it.

Citing work by Antoniou and colleagues published in 2010, Tang and Yang report that 1% AHA content can alter the pH of the outer three layers of the stratum corneum, whereas 10% can affect all ten to twenty layers. A tenfold increase in concentration is not a tenfold increase in exfoliation. It is the difference between working on the very top of the skin and working through the whole dead layer.

The same review tested glycolic acid on mouse dorsal skin at 1%, 2%, 3% and 5%. At 3% and 5% it caused skin irritation or chemical burns. At 1% and 2% it substantially reduced UVB-induced inflammatory signals including MCP-1, TNF-alpha, IL-1beta, IL-6, IL-8 and COX-2.

That is the finding that should change how Indian buyers shop. At low concentrations the same acid that burns at high concentrations was anti-inflammatory. The paper's own framing is that whether an AHA is a friend or a foe of human skin depends on its concentration. The review also notes that Taiwan's Ministry of Health and Welfare issued safety concerns specifically about chemical peeling agents containing 20% to 70% AHA at low pH, used in hospitals and clinics.

Percentage on a label is not a quality signal. It is a dose, and doses have ceilings.

What the Evidence Says About Lactic Acid on Melanin-Rich Skin

This is where lactic acid stops being a general ingredient story and becomes an Indian one.

A 2024 systematic review in the Journal of Cutaneous Medicine and Surgery, pooling 46 studies and 1,356 people with skin of colour, looked at superficial peels for post-inflammatory hyperpigmentation. Three findings are directly relevant.

1. Lactic acid held its own against a stronger acid. In a study comparing lactic acid incorporated into Jessner's peel against salicylic acid at 30%, the lactic acid group achieved a 31% reduction in the post-acne hyperpigmentation index against 25% for salicylic acid.

2. Salicylic acid's tolerability in dark skin was poor. In one salicylic acid peel study at 20% to 30% concentration, adverse effects reported after two weeks included itching in 70% of patients, redness in 40%, crusting in 40%, hyperpigmentation in 40% and hypopigmentation in 10%. Forty per cent of patients developed more pigmentation than they started with.

3. Glycolic acid outperformed salicylic acid overall in this population, with one serial glycolic acid protocol reducing a hyperpigmentation severity score by 50% after 22 weeks.

The review's conclusion on peels in general is worth carrying: people with skin of colour have a well-documented elevated risk of developing post-inflammatory hyperpigmentation after peels, so peels should not be routinely recommended as a first-line treatment in this group, though they retain merit in cases that have not responded to other options.

Professional peels and cosmetic leave-on concentrations are different things. But the direction of the evidence is consistent, and it points the same way as the concentration data above: in melanin-rich skin, the gentler acid used consistently outperforms the stronger acid used aggressively, because here irritation converts into pigment.

The Lactic Acid in a Goat Milk Bar Is Not a Lactic Acid Treatment

Vilvah is a milk-based brand, and lactic acid is what makes milk interesting to skin, so this is the section where a brand would normally overclaim. Here is the accurate version instead.

Lactic acid occurs naturally in milk, and Tang and Yang list AHAs as naturally present in foods and milk sugars. That is a genuine and interesting fact about the category Vilvah invented in India. It is not a claim that a bar of goat milk soap delivers a therapeutic AHA dose.

A rinse-off product cannot behave like a leave-on acid. Contact time is measured in seconds rather than hours, the formulation pH of a soap bar is alkaline rather than the acidic range AHAs require to work, and the lactic acid concentration in milk-derived ingredients is nowhere near cosmetic active levels. The lactic acid in a goat milk bar contributes to how the bar feels on skin. It is not exfoliating you.

If you want the AHA effect, you need a leave-on product formulated at a known concentration and a known pH. If you want the milk category benefit, that is a different and more modest thing, and Vilvah's Classic Goat Milk Soap at ₹420 should be bought for what it is rather than for what an ingredient list implies.

Vilvah, founded in 2017 in Coimbatore by Kruthika Kumaran as India's first milk-based skin and hair care brand, would rather be the brand that explains this than the brand that exploits it.

How to Use Lactic Acid Without Triggering What You Are Treating

Five rules, drawn from the evidence above rather than from convention.

1. Start at the bottom of the range and stay there for a month. The concentration data shows the gap between surface action and full stratum corneum action is large. There is no reason for a first acid to be a strong one.

2. Judge it on softness, not on stinging. Stinging is the low pH, not the efficacy. In melanin-rich skin, persistent stinging is the early signal of the inflammation that becomes a dark mark eight weeks later.

3. Wear sunscreen, without exception. AHAs increase photosensitivity and post-inflammatory hyperpigmentation recurs without adequate photoprotection. Vilvah's Skin Finish Sunscreen SPF 50 PA++++ at ₹599 uses Diethylamino Hydroxybenzoyl Hexyl Benzoate, Ethylhexyl Triazone and Bis-Ethylhexyloxyphenol Methoxyphenyl Triazine alongside Titanium Dioxide, with Niacinamide and ceramides in the base.

4. Do not stack acids with scrubs. Chemical and mechanical exfoliation together is the fastest route to the barrier damage that produces pigmentation in Fitzpatrick IV and V skin.

5. Give it twelve weeks before judging. The peel studies that showed meaningful results ran to 22 weeks. Four weeks is not an assessment period, it is an irritation period.

What Lactic Acid Will Not Do

It will not fade a dark mark on its own. Lactic acid accelerates the turnover of pigmented cells at the surface, which helps, but it does not interrupt melanin production the way a tyrosinase-targeting active does. For that, alpha arbutin and similar actives are the tool. Vilvah's Milk Drops Brightening Serum at ₹640 is formulated at pH 5.50 to 6.00 with plant-derived alpha arbutin, rice milk extract, Cystoseira tamariscifolia marine algae extract and hyaluronic acid.

It will not change your baseline skin tone, and nothing will.

It will not reach dermal pigmentation. Lactic acid is the more superficial of the two main AHAs by design, so blue-grey marks sitting in the dermis are outside its reach entirely.

And used at the wrong concentration it will do the opposite of what you bought it for. That is not a caveat added for legal cover. It is the central finding of the peer-reviewed review this article draws on, whose entire thesis is that an AHA is a friend or a foe of human skin depending on its concentration.

Frequently Asked Questions

1. What does lactic acid do for your skin?

Lactic acid is an alpha hydroxy acid that exfoliates the skin surface and hydrates it at the same time. As an exfoliant, its acidity lowers pH in the epidermis, which according to a 2018 review in Molecules inhibits transferases and kinases and interferes with ionic bond formation, causing the desmosomes that hold dead cells together to come apart and stimulating desquamation. As a hydrator, lactic acid in the form of sodium lactate is described in the same review as a well-known part of the skin's natural moisturising complex and an excellent moisturiser. That combination is unusual. Most exfoliants only exfoliate, which is why they leave skin feeling tight. Lactic acid is doing both jobs in the same application.

2. Is lactic acid or glycolic acid better?

Neither is better in the abstract, and the right question is which suits your skin. Glycolic acid is the smaller molecule, so it penetrates faster and deeper, which makes it more effective for resurfacing but also more likely to irritate. Lactic acid is larger, penetrates more slowly and stays more superficial, and it carries a humectant function that glycolic acid does not have. For dry, sensitised or reactive skin, and for anyone using an acid for the first time, lactic acid is the more forgiving starting point. For melanin-rich skin specifically, the tolerability difference matters more than the potency difference, because irritation in Fitzpatrick type IV and V skin frequently converts into post-inflammatory hyperpigmentation rather than simply fading.

3. What percentage of lactic acid should I use?

Lower than most people assume, and the evidence on dose is specific. A 2018 review in Molecules cites work by Antoniou and colleagues showing that 1% AHA content can alter the pH of only the outer three layers of the stratum corneum, while 10% can affect all ten to twenty layers. That is a large difference in depth of action from what looks like a small difference on a label. The same review tested glycolic acid on mouse skin and found that 3% and 5% caused irritation or chemical burns while 1% and 2% substantially reduced UVB-induced inflammatory markers. Start at the bottom of whatever range a product offers, use it once or twice a week, and increase only if the skin stays calm for a full month.

4. Is lactic acid safe for Indian skin and darker skin tones?

Lactic acid is among the more tolerable options for melanin-rich skin, but no acid is risk-free here. A 2024 systematic review in the Journal of Cutaneous Medicine and Surgery covering 1,356 people with skin of colour found that in a comparison of peels, lactic acid incorporated into Jessner's solution produced a 31% reduction in post-acne hyperpigmentation index against 25% for salicylic acid at 30%. The same review documented that a salicylic acid peel study reported hyperpigmentation in 40% of patients and hypopigmentation in 10% after two weeks, and concluded that chemical peels should not be routinely recommended as a first-line treatment in skin of colour. Leave-on cosmetic concentrations are much lower than professional peel concentrations, but the principle carries: use the gentlest effective dose and treat any persistent irritation as a stop signal, not a sign it is working.

5. Does goat milk soap exfoliate because it contains lactic acid?

No, and this is a claim worth being sceptical of wherever you see it. Lactic acid does occur naturally in milk, and a 2018 review in Molecules lists alpha hydroxy acids as naturally present in foods and milk sugars. But three things prevent a soap bar from acting as an AHA treatment. Contact time is seconds rather than the hours a leave-on acid gets. Soap is alkaline, while AHAs require an acidic pH to work at all. And the lactic acid concentration in milk-derived ingredients is far below cosmetic active levels. The lactic acid in a goat milk bar contributes to how it feels on skin. If you want exfoliation from lactic acid, you need a leave-on product formulated at a stated concentration and pH.

6. Can I use lactic acid with niacinamide or vitamin C?

Lactic acid and niacinamide are generally compatible, and they act at different points, with lactic acid working at the skin surface on cell turnover and niacinamide working inside the pigment pathway. The combination people should be more careful with is lactic acid and high-strength low-pH vitamin C, not because of a chemical incompatibility but because of a cumulative irritation load. Two low-pH actives in one routine on skin that pigments in response to inflammation is a poor trade. The safer structure is to separate them by time of day, or by day entirely, and to keep the total number of active ingredients in a routine low while you establish tolerance.

7. How long does lactic acid take to show results?

Longer than four weeks, which is when most people give up. The peel studies in the 2024 systematic review that produced meaningful hyperpigmentation reductions ran for up to 22 weeks, with one serial glycolic acid protocol achieving a 50% decrease in a hyperpigmentation severity score over that period. Cosmetic leave-on lactic acid works more gradually still, because it is acting more superficially and at lower concentration. Expect texture and softness changes within a few weeks, since those follow directly from improved desquamation, and give tone and mark changes three months before forming a view. The temptation at week four is to increase the concentration. In melanin-rich skin that is usually the decision that undoes the previous four weeks.

Sources

• Tang SC, Yang JH. Dual Effects of Alpha-Hydroxy Acids on the Skin. Molecules, 10 April 2018;23(4):863. https://pmc.ncbi.nlm.nih.gov/articles/PMC6017965/
• Mar K, Khalid B, Maazi M, Ahmed R, Wang OJ, Khosravi-Hafshejani T. Treatment of Post-Inflammatory Hyperpigmentation in Skin of Colour: A Systematic Review. Journal of Cutaneous Medicine and Surgery, 2024;28(5):473-480. https://pmc.ncbi.nlm.nih.gov/articles/PMC11514325/
• Lawrence E, Syed HA, Al Aboud KM. Postinflammatory Hyperpigmentation. StatPearls, NCBI Bookshelf, updated 25 November 2024. https://www.ncbi.nlm.nih.gov/books/NBK559150/