Glycolic acid has the smallest molecular weight of any AHA – 76 g/mol versus lactic acid’s 90 – which gives it better skin penetration than most of its category. This makes it the most studied and most effective AHA for changing skin structure, and also the most likely to cause irritation at equivalent concentrations.
The exfoliating mechanism is straightforward: glycolic acid weakens the ionic bonds between corneocytes in the stratum corneum, accelerating the natural desquamation process. Dead cells that would normally take longer to shed are released faster, revealing newer, smoother cells underneath. This is what drives the improvements in texture, pore appearance, and dullness that most people notice first.
At higher concentrations and with regular use, glycolic acid does more than surface exfoliation. Studies have demonstrated increased dermal hyaluronic acid production and stimulation of collagen synthesis at 8-10% concentrations with extended use. A 2013 study in the Journal of the European Academy of Dermatology and Venereology showed significant improvement in photoaged skin after 22 weeks of daily 8% glycolic acid lotion use.
Effective range for leave-on products is 5-10% at pH 3.5-4.0. Below pH 3.5, potency increases but so does irritation risk. Above pH 4.5, efficacy drops significantly – the free acid concentration, which is what does the work, falls sharply as pH rises.
If you’re new to AHAs, start with lactic acid. It’s gentler at equivalent concentrations due to its larger molecule and additional humectant properties. Glycolic acid is the logical next step when you want more exfoliating potency. Mandelic acid is the alternative for darker skin tones – glycolic acid’s speed and potency carries a higher risk of post-inflammatory hyperpigmentation in melanin-rich skin.