Hydrolyzed Soy Protein
Also known as Hydrolysed Soy Protein, Hydrolyzed Soybean Protein, Soy Protein Hydrolysate, Soya Protein Hydrolysate, Protein hydrolyzates, soya, Hydrolyzed Glycine Soja Protein, Glycine Soja (Soybean) Protein Hydrolysate, HSP
“CIR Expert Panel says: safe as used in cosmetics.”
Hydrolyzed Soy Protein (HSP; CAS 68607-88-5; EC 271-770-5) is a heterogeneous mixture of peptides and free amino acids produced by acid, alkaline, or enzymatic partial hydrolysis of glycine soja (soybean) protein. It functions in cosmetics primarily as a hair conditioning agent and skin conditioning agent. Per the 2015 CIR Concentration of Use survey, HSP has the most reported uses among the six soy-derived cosmetic ingredients (862 reported uses; ~half in non-coloring hair products) with a maximum reported use concentration of 3.5% in mascara. The CIR Final Report on Soy Proteins and Peptides (released October 22, 2015; panel meeting September 21-22, 2015; republished IJT 2023 PMID 37269084) concluded that all six soy-based ingredients including HSP are safe in cosmetics in the present practices of use and concentration — UNCONDITIONALLY, with NO molecular weight restriction analogous to the 3500 Da cap imposed on Hydrolyzed Wheat Protein. The CIR's reasoning: HSP is non-irritating in human and animal studies up to 25%, non-sensitizing in human and animal studies up to 25%, and the typical commercial MW distribution clusters in the 300-2000 Da range (well below the ~3500 Da threshold required for IgE crosslinking). The CIR explicitly noted 'No occurrences of Type 1 (i.e., immediate) hypersensitivity reactions to personal care products that contain soy peptide ingredients were reported in the public literature' as of the report. NOTABLY, a single case report published the same month as the CIR FR (Yagami et al. 2015, J Dermatol, PMID 26332460) documented one patient with cosmetic-induced percutaneous soy sensitization leading to soy food anaphylaxis — the soy parallel to the wheat-protein 'Cha no Shizuku' epidemic, but at vastly smaller scale (single case versus >2000 Japanese patients for HWP). Importantly, NO SCCS opinion on hydrolyzed soy protein exists, in contrast to HWP which received SCCS/1534/14 in 2014 in response to the wheat epidemic. This packet is the second hydrolyzed-protein entry in TheDose corpus (after Hydrolyzed Wheat Protein) and demonstrates that the multi-jurisdiction (CIR + SCCS) regulatory pattern characteristic of HWP does NOT generalize across the hydrolyzed-protein class — soy received only the CIR review, with no SCCS escalation.
Established functional uses: hair conditioning agent, skin conditioning agent, film former. Widely used (862 reported uses in cosmetics per 2015 CIR/VCRP) at typical concentrations 0.0001-3.5%.
Strong cosmetic safety profile per CIR (2015, reaffirmed 2023): non-irritating in dermal studies up to 25% in animals and humans; non-sensitizing in dermal studies up to 25% in animals and humans; non-mutagenic in S. typhimurium TA 1535/pSK1002 assay up to 5000 μg/mL with and without S9 metabolic activation.
Unconditionally approved by CIR with no MW restriction (in contrast to HWP, which is conditionally approved only at MW ≤3500 Da). The typical commercial HSP MW distribution clusters at 300-2000 Da — well below the IgE-crosslinking threshold even without an explicit regulatory cap.
Demonstrated low systemic absorption: while CIR noted 'no experimental data were available for the dermal absorption of hydrolyzed soy protein,' the panel concluded systemic toxicity from cutaneous exposure would be negligible based on water solubility, MW profile, and oral GRAS status (FDA peptone substance, 21 CFR §184.1553).
Heterogeneous mixture concern (CLASS-LEVEL): like all hydrolyzed proteins, HSP is not a single chemical entity — molecular weight distributions span 300 to <5000 Da depending on hydrolysis method. Unlike HWP, no MW restriction is mandated by CIR for HSP, but consumers and formulators cannot infer the MW profile from a label declaration alone. The general principle that polypeptides ≥30 amino acids (~3500 Da) carry IgE-crosslinking potency applies in theory to soy as it does to wheat.
Documented isolated case of cosmetic-induced soy percutaneous sensitization with food-soy anaphylaxis: Yagami et al. 2015 reported a single Japanese patient with this pattern, published the same month as the CIR Final Report (and likely not integrated into the CIR's literature review). This case is mechanistically analogous to the HWP-WDEIA pattern but lacks the epidemic scale that drove regulatory action against HWP. Continued post-market surveillance is warranted.
Soy is a major food allergen: FDA (FALCPA, 21 USC §343) and EU (Regulation 1169/2011 Annex II) require allergen labeling for soybeans in foods. EU cosmetic regulation does NOT require soy allergen labeling. For the small population of pre-existing soy-allergic individuals, dermal exposure to HSP is a theoretical risk even though CIR found no dermal reactions in HSP-naive subjects up to 25%.
Phytoestrogen residues: soybeans contain isoflavones (genistein, daidzein) with weak estrogenic activity. CIR noted hydrolysis significantly reduces phytoestrogen content but did not quantify residuals in commercial HSP. Industry-reported heavy metal limits for HSP (≤10 ppm As, 1 ppm Hg, 10 ppm Fe) appear within typical cosmetic standards.
Aerosolized exposure: HSP is reported in body/hand sprays at up to 0.021% and incidental inhalation-spray uses up to 1.3%. CIR concluded incidental inhalation does not pose additional risk because 95-99% of aerosol droplets exceed 10 μm aerodynamic diameter and would deposit in the upper airway, not the deep lung.
CIR Quick Reference Table (September 2022) — Hydrolyzed Soy Protein row: Finding=S (Safe, unconditional); Conclusion=blank (no qualificat…
CIR Final Report — Safety Assessment of Soy Proteins and Peptides as Used in Cosmetics (Burnett et al.; Status: Final Report; Release Dat…
“The CIR Expert Panel concluded that the following soy-based ingredients are safe in cosmetics in the present practices of use and concentration described in this safety assessment: glycine max (soybean) polypeptide glycine soja (soybean) peptide* glycine soja (soybean) protein hydrolyzed soy protein hydrolyzed soy protein extract* hydrolyzed soymilk protein”— soypep092015final.pdf, p. 8, CONCLUSION section