The science
The evidence for glycolic acid on body skin is older and stronger than for most cosmetic actives. In a 1996 study in the Journal of the American Academy of Dermatology, Ditre and colleagues applied a lotion containing 25% glycolic, lactic or citric acid to one forearm and a placebo to the other for an average of six months, then compared clinical measurements and biopsies: the alpha-hydroxy acid side showed a roughly 25% increase in skin thickness, more acid mucopolysaccharides, better-quality elastic fibres and denser collagen — a reversal of both epidermal and dermal markers of photoageing (Ditre et al., Journal of the American Academy of Dermatology, 1996). The forearm is body skin, the format was a leave-on lotion, and the concentration was higher than the 10% here, which makes it a reasonable ceiling for what daily glycolic use can do over months rather than a prediction for weeks.
The mechanism operates at two depths. At the surface, glycolic acid — the smallest alpha-hydroxy acid, and therefore the most penetrating — reduces corneocyte cohesion by interfering with the ionic bonds in the stratum corneum, so the thickened, compacted dead layer on shins and elbows sheds and the skin's surface becomes smoother and better able to hold water; glycolic acid is also itself a humectant. Deeper, sustained use has been associated in histological studies with increased epidermal thickness and dermal glycosaminoglycan and collagen synthesis, which is the basis for the lotion's tone and texture claims over months. Both effects depend on the acid being at a working pH; partial neutralisation with sodium hydroxide, as here, balances activity against tolerance.
The supporting cast is more than filler. Tetrahexyldecyl ascorbate is a lipid-soluble vitamin C ester that is stable in an emulsion and penetrates the stratum corneum, with evidence for antioxidant activity and modest tone benefit in leave-on use; paired with tocopheryl acetate it gives the lotion a genuine antioxidant profile that most body exfoliants lack. Shea butter and glycerin address the transepidermal water loss that any exfoliant temporarily increases. Chamomile and allantoin have long records for reducing erythema, and grape seed, green tea and willowherb extracts supply polyphenols with antioxidant and anti-inflammatory activity in vitro. The known limitations are those of the acid class: alpha-hydroxy acids increase UV sensitivity — the FDA's own review of AHA safety underpins the daily-sunscreen instruction — and a 10% concentration over large areas can produce stinging and desquamation on compromised or freshly shaved skin, which is the tolerance trade-off for the resurfacing benefit.
References 1 ShowHide
- Effects of alpha-hydroxy acids on photoaged skin: a pilot clinical, histologic, and ultrastructural study — Journal of the American Academy of Dermatology (1996)