In the alpha hydroxy acid world, certain players — we’re looking at you, glycolic acid — seem to get all the attention. But recent studies have demonstrated the effectiveness of lactic acid for managing a similar range of skin concerns.

So what’s the difference between glycolic acid and lactic acid — and is one of them better? We’ve got the lowdown below.

What is glycolic acid?

We’ve talked a lot about AHA superstar glycolic acid, and how it benefits the skin. Here’s a quick summary of its characteristics and benefits:

• Smallest of the alpha hydroxy acids, so it penetrates the deepest
• Water soluble, derived from sugar cane
• Found in lower concentrations over-the-counter, and higher for in-office peels
• Known for its exfoliating keratolytic abilities, breaking the bonds between dead skin cells
• Stimulates collagen, elastin and glycosaminoglycans (natural skin hydrators)

What is lactic acid?

Though it doesn’t typically receive as much attention as some of its alpha hydroxy cousins, lactic acid has its own unique attributes — including its skin-smoothing abilities, favored by Cleopatra.

• Same substance produced by muscles during intensive workouts
• Water soluble AHA found in sour milk, but synthetically produced for skincare
• Found in lower concentrations over-the-counter, and higher for in-office peels
• Recent studies show it's as effective in exfoliating peels as glycolic acid, but gentler
• Part of the skin’s natural moisturizing complex 
• Contributes to the skin cell cycle
• Research suggests it may play an anti-inflammatory role in skin

Do glycolic acid and lactic acid do the same thing?

Because they’re chemically similar, alpha hydroxy acids (like glycolic, lactic, malic and citric) do share a lot in common. Glycolic acid is likely the most studied of the AHAs, and is used to manage a wide variety of skin concerns, including:

• Premature aging — hyperpigmentation, dullness, fine lines
• Acne — both breakouts and acne scarring
• Keratosis pilaris — that bumpy, dry “chicken skin”

In recent years, scientists have discovered that lactic acid is beneficial for treating the same types of conditions as glycolic acid — including photoaging, acne and KP — but with the added bonus of being less irritating for those with sensitive skin (more on that below).

What’s the difference between glycolic acid and lactic acid?

As we summarized above, these two AHAs have a lot in common. They’re both excellent exfoliators that can help alleviate dullness, fine lines, and hyperpigmentation, as well as acne and acne scarring. The main differences between these two stem from their molecular structure:

• Firstly, glycolic acid is smaller and penetrates deeper, whereas lactic acid is a bit larger and remains more superficial.  This makes lactic acid the more universally tolerated of the two AHAs.
• Secondly, there are functional differences between these two ingredients — beyond exfoliating— that are worth noting:
• Glycolic acid boosts production of natural skin hydrators like hyaluronic acid, and stimulates fibroblasts in the dermis to create more collagen and elastin.
• Lactic acid is one of skin’s natural moisturizing factors (NMF), essential to healthy barrier function, while it also promotes collagen production.

Can you use glycolic acid and lactic acid together?

Because these two alpha hydroxy acids have slightly different benefits, it’s only natural to lean toward incorporating them both into your skincare routine. But be careful: combining these two means you’re doubling up on exfoliating, which can irritate your skin and compromise its natural barrier function — which in turn could promote premature aging and/or acne.

How to combine glycolic acid and lactic acid

Remember, these are both potent exfoliants, so doubling up without reducing either the concentration, the application frequency, (or both) is likely to cause problems.

Here’s how to combine glycolic acid and lactic acid safely:

• Use them at different times in your routine. For example, try a glycolic acid scrub one day, and a lactic acid lotion another day. Check your skin for signs of dryness or irritation, and dial back your product use if necessary.
• Choose a high-quality formulation that already contains both ingredients. Opt for a product that has safe concentrations of both acids and follow the labeling instructions. This ensures that you won’t be overdoing it. Try these two from SLMD Skincare:
• For face: AHA/BHA Swipes contain a combination of salicylic, glycolic and lactic acids to gently exfoliate, helping to keep pores clear and prevent dullness. They’re ideal for anti-aging as well, just be sure to ease into use if your skin is dry or sensitive.
• For body: Glycolic Acid Body Scrub contains a combination of both physical and chemical exfoliants. This sloughs away dead skin cells that can build up to cause keratosis pilaris, or clog pores.