Hydrolyzed Soy Flour

Hydrolyzed soy flour is primarily a protein-derived conditioning/film-forming ingredient used at low concentrations, and it is not a classic irritant like acids or solvents. However, soy proteins are recognized allergens and can trigger contact urticaria or eczematous flares in sensitized individuals, with higher risk on compromised skin due to increased penetration. Given the nontrivial sensitization potential despite generally mild use levels, I rate it as mild (0.4) rather than “gentle.” Safety Notes: In commercial skincare, hydrolyzed soy flour is most often used as a minor conditioning/film-forming botanical protein, with trace-to-low inclusion levels (~0.01–0.1%) common in mass-market lotions, cleansers, and shampoos where it functions as a label-friendly additive. Higher-use levels are seen in consumer-available “soy protein/peptide” firming creams, masks, and hair repair treatments, where total hydrolyzed soy-derived solids can reach ~1–5% before texture, odor/color, and stability constraints typically limit further increases. Leave-on products more commonly sit in the ~0.05–2% range, while rinse-off can span similar lows but usually tops out lower unless positioned as a protein-repair treatment.