Glycolic acid vs lactic acid explained

Glycolic acid and lactic acid are often spoken about as if they are interchangeable, i.e. one and the same, but they’re far from identical. Both are alpha hydroxy acids (AHAs) and both help loosen dead skin cells from the surface, to improve texture and tone. Yet, their behaviour on the skin, how far they travel, how quickly they work and how the skin reacts - is different enough to matter when choosing between the two. It’s not simply a case of strength, but rather the type of exfoliation your skin can handle.

What is glycolic acid?

Typically derived from sugarcane, glycolic acid is the smallest AHA molecule of the AHA family. Because of that size, it can penetrate the outer layers of the skin like a breeze.

And because it’s able to go beyond the surface, glycolic acid is highly effective when it comes to tackling dullness, uneven tone caused by sun damage or hyperpigmentation, as well as visible texture.

How glycolic acid works

Glycolic acid isn’t a physical exfoliant that buffs away the top layers of dead skin cells. Instead, “it dissolves the gluelike bonds that hold dead cells in place, allowing them to come away evenly, to reveal fresh skin underneath,” says Aesthetic Doctor, Ahmed El Muntasar.

It also attracts water, aiding in boosting the hydration levels of the skin, which means the skin often looks radiant and plump once the surface cell buildup is gone. And if that weren’t enough, longerterm use has been linked to improvements in elasticity (think snatched contours) likely because fresher skin is better able to hold moisture.

And it’s these combined effects that explain why glycolic acid is often recommended when the goal is a more even-toned, glowing complexion.

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Where glycolic acid excels beyond the face

Glycolic acid isn’t only used on the face. Underarms, for instance, often benefit from this exfoliant. “Regularly applying a glycolic acid toner or serum to the underarm area can help with discolouration, texture and even odour control, by breaking down dead skin cells that trap bacteria,” says Aesthetic Doctor Raquel Amado.

Its ability to prevent buildup also makes it useful for ingrown hairs. “By sloughing off dead cells, it allows ingrown hairs to emerge without obstruction, reducing bumps and inflammation,” adds Amado.

Scalp care is another growing use. In low concentrations, glycolic acid helps remove product buildup and dead skin. “Just like on the face, glycolic acid helps clear away any barrier that might be preventing the scalp from absorbing moisture or nutrients,” notes Amado.

Keratosis pilaris (the small bumps often seen on arms or thighs) responds well too. “By loosening the buildup of keratin in hair follicles, glycolic acid can reduce the appearance of these raised bumps,” says El Muntasar.

Lactic acid explained

Lactic acid has a larger molecular size, than its fellow AHA, which results in it travelling more slowly and sticking closer to the surface of the skin. Earlier sources used in skincare came from fermented milk, but plantbased sources are the most commonly used variety in today’s formulas.

It’s known to cause less irritation than other exfoliating acids because it doesn’t penetrate as deeply, and yet it still smooths and brightens - but at a more measured pace. And like glycolic acid, it also draws moisture into the skin, which makes it kinder to dry or sensitive skin types.

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How to use AHAs safely

Both acids need a gradual introduction, so start with one to two evenings a week and then build up to two to three. You may tolerate four to seven days a week depending on the concentration, but most people do well using them two to three times a week. Do be aware that using them alongside retinoids or other strong actives can increase irritation unless you alternate them, so monitor your skin closely when introducing either one of these AHAs.

Daily sunscreen is essential, as newly exposed skin is more prone to UV damage, and using AHAs without SPF can lead to pigmentation. And be sure to support your skin barrier with ingredients like ceramides, peptides and niacinamide to help keep the skin healthy and balanced.

Choosing the right acid for your routine

Penetration depth is the key dividing line between these two AHAs. Glycolic acid reaches deeper and tends to create more obvious changes in texture and tone. Lactic acid sits higher on the surface, producing a gentler result that is often better tolerated, but still offers a healthy glow.

Glycolic acid suits resilient skin and those addressing sun damage or pigmentation. While lactic acid is the more predictable option for reactive skin, dry complexions, or anyone who has found stronger acids uncomfortable.

Both can be highly effective when matched to the skin’s needs, however, consistency is what delivers smoother, more eventoned skin over time.