Arginine HCl (L-arginine monohydrochloride) is the hydrochloride salt of L-arginine, a cationic α-amino acid. In topical skincare, the arginine moiety acts as a skin-conditioning humectant aligned with the skin’s natural moisturizing architecture: amino acids and their derivatives are principal constituents of the Natural Moisturizing Factor (NMF), which supports stratum corneum hydration and enzyme function. The positively charged guanidinium side chain (very high basicity) imparts strong electrostatic interactions with the skin surface, aiding feel and water binding. As the HCl salt, Arginine HCl is highly water-soluble and compatible with mildly acidic systems (e.g., AHA toners, vitamin C derivatives), offering formulators a way to deliver an amino-acid benefit without forcing the pH upward. Regulatory and safety assessments covering α-amino acids and their simple salts support its low irritation and sensitization potential at cosmetic use levels.

In hair care, arginine is a known fiber-interactive amino acid that associates with keratin’s acidic sites, enhancing substantivity and combability. Research indicates arginine can help mitigate oxidative coloring/bleaching damage and increase deposition/retention of beneficial materials on hair surfaces, translating into improved tensile properties and reduced breakage in color-care and repair systems. Because arginine remains cationic across cosmetic pH ranges, Arginine HCl can support conditioning and antistatic effects in shampoos, conditioners, masks, leave-ins, and scalp treatments, particularly when paired with cationic polymers or protein fragments designed to bond to damaged cuticles.