Asparagine

Asparagine is a naturally occurring amino acid used in skincare mainly as a skin-conditioning/humectant support ingredient, typically at low concentrations. Amino acids are generally well-tolerated and have low irritancy in patch testing when formulated at physiologic pH, but they are not completely inert and can occasionally sting on severely compromised barriers (e.g., active eczema or post-procedure skin). Given its low intrinsic reactivity yet non-zero risk in highly sensitized populations, a very gentle score is most appropriate. Safety Notes: In commercial skincare, asparagine is most often used as a minor component of amino-acid/NMF blends where it appears at trace-to-low levels (often via multi-amino-acid complexes), yielding effective use levels down to ~0.0001% in finished products. Standalone or amino-acid-focused hydrating/conditioning serums and masks sold OTC can push individual amino acids into the ~0.5–2% range, with ~2% representing the upper end typically seen before sensory, solubility, and formula balance constraints make higher levels uncommon. Usage is primarily in leave-on moisturizers/serums and sheet masks, with rinse-off cleansers generally at the low end due to brief contact time.