Method of improving the appearance of the skin

Compound I A cosmetic method of improving the appearance of the skin of a subject, comprising steps: (i) topically applying a composition comprising L-4-thiazolylalanine (Compound I) or a zwitterionic form or cosmetically-acceptable salt thereof, in an amount of 0.08-0.50 wt% of the composition's total weight; (ii) repeating step (i) for a continuous period of at least 24 days and until a cosmetically beneficial improvement to the skin has occurred. Step (ii) may comprise repeating step (i) at least once per day, every other day, or at least five of every seven consecutive days. The improvement to the skin may comprise: reduced wrinkle depth, increased hyaluronic acid secretion, increased hydration, firmness, and smoothness; increased epidermal thickness; improved skin barrier integrity; reduced redness (erythema), and/or increased dermal collagen II and/or collagen I production. Also claimed is a composition for topical application comprising Compound I or a zwitterionic or cosmetically acceptable salt thereof, at 0.08-0.50 wt% of the composition's total weight.