Histidine
Also known as L-Histidine, Histidine, (S)-2-Amino-3-(1H-imidazol-4-yl)propanoic acid
“CIR Expert Panel says: safe as used in cosmetics.”
Histidine (CAS 71-00-1) is an essential proteinogenic α-amino acid with an imidazole side chain, used in cosmetics as an NMF (natural moisturizing factor) component and humectant. The CIR Expert Panel assessed all 21 α-amino acids used in cosmetics (Burnett et al., IJT 32(Suppl. 4):41S-64S, 2013; PMID 24335967) and explicitly named Histidine in the conclusion as safe in the present practices of use and concentration. The QRT records Histidine with Finding=S (Safe), no qualifying conditions, same citation. Histidine HCl (the hydrochloride salt form) carries the same S finding in the same assessment.
Proteinogenic α-amino acid: essential amino acid (humans cannot synthesize it endogenously) with a basic imidazole side chain conferring metal-chelating and pH-buffering properties
Natural moisturizing factor (NMF) component: free histidine is found in the stratum corneum where it contributes to skin hydration and barrier integrity
Humectant: attracts and binds water via the imidazole nitrogen atoms; the imidazole ring also acts as an antioxidant via metal ion chelation
CIR Expert Panel concluded Histidine is safe as used in cosmetics in the present practices of use and concentration:41-64, 2013; QRT Finding=S)
Used in skin- and hair-conditioning formulations; supports barrier repair in combination with ceramides and fatty acids
- · Histidine is the precursor to histamine via enzymatic decarboxylation; this pathway is biologically significant but not a concern in topical cosmetic application at typical use concentrations
- · No known sensitization or irritation reported in the CIR group assessment at cosmetic-use concentrations
CIR Quick Reference Table (October 2024) — Histidine row: Finding=S, Citation=IJT 32(Suppl. 4):41-64, 2013
“Histidine | S | | IJT 32(Suppl. 4):41-64, 2013”— QRT-Update-100824_0.pdf, p. 124