Hydrolyzed Soy Protein

Hydrolyzed soy protein is a film-forming/humectant conditioning ingredient typically used at low concentrations (~0.1–2%), and it is generally well tolerated in leave-on and rinse-off products. However, protein hydrolysates can act as contact allergens/irritants in a meaningful minority of reactive or eczematous patients, with documented cases of dermatitis from hydrolyzed plant proteins, so I score it as mild to reflect occasional sensitivity risk. In compromised skin barriers, I advise caution and patch testing because reactions, while uncommon, can be clinically significant when they occur. Safety Notes: In commercial skincare and haircare, hydrolyzed soy protein is often used at very low levels (~0.01–0.1%) as a label-claim conditioning/film-forming agent in leave-on lotions/serums and in rinse-off cleansers/shampoos where it functions mainly as a minor feel enhancer. Most mainstream products sit around ~0.2–2% depending on the supplier active strength and desired conditioning effect, while high-strength consumer-available masks, hair treatments, and some firming/conditioning leave-on formulas can reach about 3–5% total hydrolyzed soy protein before sensory, tack/film feel, and stability/compatibility constraints become limiting; no specific EU/FDA cosmetic concentration cap applies, so the upper end is governed primarily by formulation performance.