THE SCIENCE OF LACTIC ACID

Lactic acid is one of the most effective and misunderstood ingredients in skincare. It exfoliates, hydrates, brightens, and supports long-term skin health - all at once. But how does it actually work at a molecular level? And why does Sunday Riley's Good Genes All-In-One Lactic Acid Treatment remain one of the most cult-followed formulas in modern skincare? Here's the full science.

Ingredient PROFILE

 What Exactly Is Lactic Acid?

Lactic acid is an alpha hydroxy acid (AHA) - a class of well-researched acids with decades of use in both dermatology and cosmetic formulation. Sunday Riley's Good Genes Lactic Acid uses a purified-grade lactic acid formulated for high efficacy and tolerability across skin types. What sets it apart within the AHA family is its larger molecular size. It works closer to the skin's surface than smaller AHAs - which means gentler, more tolerable exfoliation - especially for sensitive or reactive skin types.
 

It's worth comparing it directly to glycolic acid - the smallest AHA molecule and the hero ingredient in Sunday Riley's Good Genes Glycolic. Because glycolic's molecule is smaller, it penetrates more deeply and acts faster - making it ideal for resilient skin dealing with significant texture or sun damage. Lactic acid delivers comparable brightening and exfoliation with a gentler touch. Backed by decades of dermatological research, they're not trend ingredients - they're two precision tools built for the same goal, designed for different skin types.

How Does Lactic Acid Exfoliate the Skin?

Your skin naturally sheds dead cells through a process called desquamation. As you age, or when skin is dehydrated, stressed, or sun-damaged, this process slows. Dead cells pile up on the surface, leading to dullness, rough texture, uneven tone, and clogged pores.
 

Lactic acid works by dissolving the bonds (desmosomes)that hold dead cells together at the surface. Rather than physically scrubbing them away, it chemically loosens them so they shed more evenly and naturally. The result: faster cell turnover, smoother texture, and a more radiant complexion - often visible within days.
 

Sunday Riley's Good Genes Lactic uses a purified, high-potency lactic acid formulated to deliver these results without the sting or sensitivity often associated with stronger AHAs.

Does Lactic Acid Hydrate Skin - or Just Strip It?

This is where lactic acid separates itself from other acids. Unlike some exfoliants that leave skin feeling tight and dry, lactic acid is also a humectant - it attracts and retains moisture in the skin. It does this by stimulating natural moisturizing factors (NMFs) and by increasing ceramide synthesis, which strengthens the skin barrier.

In short: it exfoliates and hydrates simultaneously. That dual action is rare and valuable - especially for dry or dehydrated skin types who want the glow of chemical exfoliation without the dryness trade-off.

What Does Lactic Acid Do for Dark Spots and Hyperpigmentation?

Lactic acid is a clinically recognized skin brightening agent. It works two ways: accelerating cell turnover so pigmented cells shed faster, and inhibiting tyrosinase - the enzyme responsible for melanin (pigment) production. This dual mechanism fades [3]dark spots, post-breakout marks, sun damage, and uneven tone over consistent use.
 

Good Genes Lactic amplifies this with licorice root (a natural brightener) and arnica (to calm inflammation), creating a formula that addresses both the cause and appearance of discoloration.

Is Lactic Acid Safe for Sensitive Skin?

Yes and it's often the preferred acid for sensitive skin types. Its larger molecular size means it works at the surface rather than penetrating deeply, reducing the risk of irritation, redness, or over-exfoliation. Used correctly, it can actually strengthen the skin barrier over time rather than compromising it.
 

That said, all exfoliating acids increase photosensitivity - sunscreen every morning is non-negotiable. Start 2–3 nights per week and build from there.

How Does Lactic Acid Fit Into a Full Skincare Routine?

 Lactic acid is most often used in the PM routine, after cleansing and before oils or moisturizer. Treatments like Good Genes are designed to be left on as an overnight serum-no rinse required. On nights you’re not using a retinoid (like Luna or A+), this is an ideal active step.
 

For those who prefer a more immediate glow, lactic acid can also be used in the morning to help skin look smoother and more radiant throughout the day. When using in the AM, always follow with sunscreen, as exfoliating acids can increase sun sensitivity.
 

Avoid layering lactic acid with other low-pH actives in the same routine (like applying both Vitamin C and Lactic acid at once), unless your skin is well-acclimated.

Instead, separate your actives, use vitamin C in the morning, and alternate lactic acid and retinoids in your evening routine, for a balanced, non-irritating approach.

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