A gentler AHA that also draws in water. As a 12% ammonium lactate lotion it has good trial evidence for very dry, rough and scaly skin.
Lactic acid is an AHA slightly larger than glycolic acid and part of the skin's own natural moisturizing factor, so besides loosening dead cells it acts as a humectant. Ammonium lactate is lactic acid partly neutralized with ammonia; at 12% it is a long-standing treatment for severe dry skin (xerosis), rough bumpy skin on the arms and legs, and inherited scaling conditions.
It shows up mostly in body lotions and 'smoothing' creams for rough skin.
A double-blind trial found 12% ammonium lactate lotion outperformed 5% lactic acid lotion for moderate to severe dry skin, with benefits lasting through a 3-week break. An 8% L-lactic acid cream modestly improved photodamage, mottled pigment and roughness in a 22-week vehicle-controlled trial. The trials are older and moderate in size.
In a double-blind trial in moderate to severe dry skin, 12% ammonium lactate lotion twice daily reduced xerosis more than 5% lactic acid lotion over 3 weeks, and the advantage held through a 3-week no-treatment period.
74 women with photodamaged skin used 8% glycolic acid, 8% L-lactic acid or vehicle cream twice daily for 22 weeks; at least one grade of facial improvement was seen in 76%, 71% and 40% respectively. Lactic acid also improved mottled pigment and roughness on the forearms. Benefits were modest and the creams well tolerated.