Glycolic Acid vs Lactic Acid: Which AHA Should You Use?

Glycolic Acid vs Lactic Acid: A Direct Comparison

Both are alpha hydroxy acids. Both exfoliate. But they behave differently on skin — and choosing the wrong one can lead to irritation or underwhelming results.

Molecular Size: The Key Difference

Glycolic acid has the smallest molecular structure of any AHA. This means it penetrates deeper into the epidermis faster than any other acid. Lactic acid has a larger molecule — it stays closer to the surface and penetrates more slowly.

This single fact explains most of the practical differences:

	Glycolic Acid	Lactic Acid
Molecular weight	76 Da (smallest AHA)	90 Da
Penetration depth	Deep	Surface-level
Effective concentration	5–10%	5–12%
Exfoliation strength	Strong	Moderate
Humectant properties	No	Yes — attracts moisture
Best for	Anti-aging, uneven texture	Beginners, dry/sensitive skin
Irritation risk	Higher	Lower

When to Choose Glycolic Acid

Use glycolic if you:

• Have normal to oily skin that tolerates actives well
• Want to address deeper texture concerns, fine lines, or significant hyperpigmentation
• Have used lactic acid without issue and want to upgrade
• Are treating sebaceous filaments or rough skin texture

When to Choose Lactic Acid

Use lactic if you:

• Are new to chemical exfoliation
• Have dry or sensitive skin (lactic acid's humectant effect actually hydrates as it exfoliates)
• Want gentler, more gradual results
• Have redness, reactive skin, or compromised barrier

Can You Use Both?

Yes — alternating acids is a legitimate strategy. Use lactic acid 3x/week for baseline maintenance and glycolic acid once a week for deeper exfoliation. Avoid using both on the same night.

The Bottom Line

For most people starting exfoliation, lactic acid is the smarter entry point — it delivers real results without the irritation risk of glycolic. Once your skin is adapted, consider switching to or adding glycolic for enhanced efficacy.