Silk

In skincare, “silk” typically refers to silk protein/sericin or hydrolyzed silk used at low concentrations as a film-forming conditioner, which is generally well tolerated and not intrinsically irritating like acids or solvents. However, as a protein-derived material it carries a non-zero risk of irritation or sensitization in highly reactive or eczema-prone patients (especially on compromised skin), and formulation impurities can increase reactivity. Given this small but real risk, it fits best as a gentle ingredient rather than inert. Safety Notes: In commercial skincare, silk is most often used as hydrolyzed silk/silk amino acids at very low levels (about 0.01–0.3%) as a marketing/skin-feel and conditioning additive in leave-on lotions, serums, and rinse-off cleansers. Higher-strength consumer-available products (e.g., specialty “silk protein” creams, masks, and concentrated hair/skin conditioning treatments) commonly reach ~1–3%, with a practical upper end around 5% due to solubility/viscosity, odor/color, and stability constraints rather than explicit regulatory limits.