Abstract
The stratum corneum (SC) is essential for maintaining skin barrier integrity through coordinated interactions between corneocytes, intercellular lipids, and natural moisturizing factors (NMFs). Lactate is a key NMF component that contributes to hydration, pH regulation, and enzymatic activity within the SC. Recent advances in understanding the distinctions between lactate, lactic acid, and ammonium lactate have clarified their respective roles within the skin, providing a novel framework for their clinical use. The use of ammonium lactate, a pH-balanced source of L-lactic acid, in skincare offers a biomimetic approach to restoring skin barrier function. Its activity is governed by pH-dependent equilibrium and diffusion processes within the SC, enabling targeted availability of L-lactic acid in superficial layers where xerotic changes are most pronounced. Mechanisms of action include humectant effects, normalization of desquamation, and support of epidermal homeostasis. Clinical relevance extends across xerotic and hyperkeratotic conditions, including atopic dermatitis, ichthyosis, and psoriasis, as well as in skin of color, where xerosis may present as visible ashy skin. Benefit has also been shown in conditions such as acanthosis nigricans. This review summarizes the mechanistic and clinical rationale supporting ammonium lactate as a physiologically aligned and increasingly well-characterized therapeutic option.  .