{
  "$schema": "https://foodadditiveindex.com/api/v1/schema.json",
  "id": "https://foodadditiveindex.com/additives/l-cysteine",
  "slug": "l-cysteine",
  "name": "L-Cysteine",
  "identifiers": {
    "e_number": "E920",
    "ins_number": null,
    "cas_number": "52-90-4",
    "inchikey": "XUJNEKJLAYXESH-REOHCLBHSA-N",
    "pubchem_cid": 5862
  },
  "functional_class": null,
  "summary": "L-Cysteine is a dough conditioner that relaxes gluten, cutting the mixing and proving time of industrial bread. It is the additive most often raised as a dietary question, because one historic production route was hydrolysis of human hair and poultry feathers.",
  "derivation_summary": "Now produced chiefly by bacterial fermentation, and also by extraction from keratin — duck and chicken feathers, hog bristle, and historically human hair. Manufacturers need not declare which route was used.",
  "regulatory_status": [
    {
      "jurisdiction": "US",
      "jurisdiction_name": "United States",
      "authority": "Food and Drug Administration",
      "status": "permitted",
      "status_label": "Permitted",
      "provision_count": 1,
      "provisions": [
        {
          "status": "permitted",
          "food_category": null,
          "max_level": null,
          "max_level_unit": null,
          "conditions": null,
          "effective_from": null,
          "citation": {
            "ref": "21 CFR 184.1271",
            "url": "https://www.ecfr.gov/current/title-21/section-184.1271"
          },
          "source": "ecfr",
          "retrieved_at": "2026-09-07T18:25:51.549Z"
        }
      ]
    },
    {
      "jurisdiction": "CODEX",
      "jurisdiction_name": "Codex Alimentarius",
      "authority": "Codex Alimentarius Commission / JECFA",
      "status": "not_listed",
      "status_label": "Not listed",
      "note": "Does not appear on this jurisdiction’s permitted list. That is not the same as being prohibited.",
      "provision_count": 0,
      "provisions": []
    }
  ],
  "names": [
    {
      "name": "202114-66-7",
      "type": "cas",
      "source": "pubchem"
    },
    {
      "name": "52-90-4",
      "type": "cas",
      "source": "openfoodtox"
    },
    {
      "name": "56-89-3",
      "type": "cas",
      "source": "openfoodtox"
    },
    {
      "name": "(2R)-2-amino-3-mercapto-propionic acid;hydrochloride",
      "type": "common",
      "source": "pubchem"
    },
    {
      "name": "(2R)-2-amino-3-mercaptopropanoate",
      "type": "common",
      "source": "pubchem"
    },
    {
      "name": "(2R)-2-amino-3-mercaptopropanoic acid",
      "type": "common",
      "source": "pubchem"
    },
    {
      "name": "(2R)-2-amino-3-sulfanyl-propanoic acid",
      "type": "common",
      "source": "pubchem"
    },
    {
      "name": "(2R)-2-amino-3-sulfanylpropanoate",
      "type": "common",
      "source": "pubchem"
    },
    {
      "name": "(2R)-2-amino-3-sulfanylpropanoic acid",
      "type": "common",
      "source": "pubchem"
    },
    {
      "name": "(2R)-2-azaniumyl-3-sulfanylpropanoate",
      "type": "common",
      "source": "pubchem"
    },
    {
      "name": "(R)-(+)-Cysteine",
      "type": "common",
      "source": "pubchem"
    },
    {
      "name": "(R)-2-Amino-3-mercaptopropanoic acid",
      "type": "common",
      "source": "pubchem"
    },
    {
      "name": "(R)-2-Amino-3-mercaptopropionic acid",
      "type": "common",
      "source": "pubchem"
    },
    {
      "name": "(R)-2-Amino-3-sulfanyl-propanoic acid",
      "type": "common",
      "source": "pubchem"
    },
    {
      "name": "(R)-Cysteine",
      "type": "common",
      "source": "pubchem"
    },
    {
      "name": "2-amino-3-mercaptopropanoate",
      "type": "common",
      "source": "pubchem"
    },
    {
      "name": "2-Amino-3-mercaptopropanoic acid",
      "type": "common",
      "source": "pubchem"
    },
    {
      "name": "2-Amino-3-mercaptopropanoic acid, (R)-",
      "type": "common",
      "source": "pubchem"
    },
    {
      "name": "2-Amino-3-mercaptopropionic acid",
      "type": "common",
      "source": "pubchem"
    },
    {
      "name": "2-amino-3-sulfanylpropanoic acid",
      "type": "common",
      "source": "pubchem"
    },
    {
      "name": "2-azaniumyl-3-sulfanylpropanoate",
      "type": "common",
      "source": "pubchem"
    },
    {
      "name": "[R-(R*,R*)]-3,3'-dithiobis [2-aminopropanoic acid]",
      "type": "common",
      "source": "openfoodtox"
    },
    {
      "name": "alpha-Amino-beta-mercaptopropanoic acid, L-",
      "type": "common",
      "source": "pubchem"
    },
    {
      "name": "alpha-Amino-beta-mercaptopropionic acid, L-",
      "type": "common",
      "source": "pubchem"
    },
    {
      "name": "alpha-Amino-beta-thiolpropionic acid",
      "type": "common",
      "source": "pubchem"
    },
    {
      "name": "alpha-Amino-beta-thiolpropionic acid, L-",
      "type": "common",
      "source": "pubchem"
    },
    {
      "name": "beta-Mercaptoalanine",
      "type": "common",
      "source": "pubchem"
    },
    {
      "name": "beta-Mercaptoalanine, L-",
      "type": "common",
      "source": "pubchem"
    },
    {
      "name": "bis(β-amino-β-carboxyethyl) disulfide",
      "type": "common",
      "source": "openfoodtox"
    },
    {
      "name": "CCRIS 912",
      "type": "common",
      "source": "pubchem"
    },
    {
      "name": "cisteina",
      "type": "common",
      "source": "pubchem"
    },
    {
      "name": "Cisteinum",
      "type": "common",
      "source": "pubchem"
    },
    {
      "name": "Cisteinum (Latin)",
      "type": "common",
      "source": "pubchem"
    },
    {
      "name": "Cys",
      "type": "common",
      "source": "pubchem"
    },
    {
      "name": "CYSTE",
      "type": "common",
      "source": "openfoodtox"
    },
    {
      "name": "Cystein",
      "type": "common",
      "source": "pubchem"
    },
    {
      "name": "cysteine",
      "type": "common",
      "source": "pubchem"
    },
    {
      "name": "Cysteine, L-",
      "type": "common",
      "source": "pubchem"
    },
    {
      "name": "Cysteinum",
      "type": "common",
      "source": "pubchem"
    },
    {
      "name": "Dicysteine",
      "type": "common",
      "source": "openfoodtox"
    },
    {
      "name": "E 920",
      "type": "common",
      "source": "openfoodtox"
    },
    {
      "name": "FEMA No. 3263",
      "type": "common",
      "source": "pubchem"
    },
    {
      "name": "FREE CYSTEINE",
      "type": "common",
      "source": "pubchem"
    },
    {
      "name": "Gelucystine",
      "type": "common",
      "source": "openfoodtox"
    },
    {
      "name": "H-Cys-OH",
      "type": "common",
      "source": "pubchem"
    },
    {
      "name": "Half cystine",
      "type": "common",
      "source": "pubchem"
    },
    {
      "name": "Half-cystine",
      "type": "common",
      "source": "pubchem"
    },
    {
      "name": "HSDB 2109",
      "type": "common",
      "source": "pubchem"
    },
    {
      "name": "L Cysteine",
      "type": "common",
      "source": "pubchem"
    },
    {
      "name": "L-(+)-Cysteine",
      "type": "common",
      "source": "pubchem"
    },
    {
      "name": "L-2-Amino-3-mercaptopropanoic acid",
      "type": "common",
      "source": "pubchem"
    },
    {
      "name": "L-2-Amino-3-mercaptopropionic acid",
      "type": "common",
      "source": "pubchem"
    },
    {
      "name": "L-Alanine, 3-mercapto-",
      "type": "common",
      "source": "pubchem"
    },
    {
      "name": "L-Cys",
      "type": "common",
      "source": "pubchem"
    },
    {
      "name": "l-cystAine",
      "type": "common",
      "source": "pubchem"
    },
    {
      "name": "L-Cystein",
      "type": "common",
      "source": "pubchem"
    },
    {
      "name": "L-cysteine",
      "type": "common",
      "source": "openfoodtox"
    },
    {
      "name": "L-Cysteine 7403",
      "type": "common",
      "source": "pubchem"
    },
    {
      "name": "L-Cysteine from non-animal source",
      "type": "common",
      "source": "pubchem"
    },
    {
      "name": "L-Cysteine High",
      "type": "common",
      "source": "pubchem"
    },
    {
      "name": "L-Cysteine High 7404",
      "type": "common",
      "source": "pubchem"
    },
    {
      "name": "l-cysteinum",
      "type": "common",
      "source": "pubchem"
    },
    {
      "name": "L-cystine",
      "type": "common",
      "source": "openfoodtox"
    },
    {
      "name": "L-Zystein",
      "type": "common",
      "source": "pubchem"
    },
    {
      "name": "Propanoic acid, 2-amino-3-mercapto-, (R)-",
      "type": "common",
      "source": "pubchem"
    },
    {
      "name": "Thioserine",
      "type": "common",
      "source": "pubchem"
    },
    {
      "name": "α-diamino-beta-dithiolactic acid",
      "type": "common",
      "source": "openfoodtox"
    },
    {
      "name": "β,β'-diamino-β,β'-dicarboxydiethyl disulfide",
      "type": "common",
      "source": "openfoodtox"
    },
    {
      "name": "β,β'-dithiodialanine",
      "type": "common",
      "source": "openfoodtox"
    },
    {
      "name": "E920",
      "type": "e_number",
      "source": "openfoodtox"
    },
    {
      "name": "E921",
      "type": "e_number",
      "source": "pubchem"
    },
    {
      "name": "(2R)-2-amino-3-[[(2R)-2-amino-2-carboxyethyl]disulfanyl]propanoic acid",
      "type": "iupac",
      "source": "openfoodtox"
    },
    {
      "name": "(2R)-2-amino-3-sulfanylpropanoic acid",
      "type": "iupac",
      "source": "openfoodtox"
    },
    {
      "name": "L-Cysteine",
      "type": "label",
      "source": "ecfr"
    }
  ],
  "hazard_reference_values": [],
  "sources": [
    {
      "key": "ecfr",
      "name": "Electronic Code of Federal Regulations, Title 21",
      "publisher": "U.S. Government Publishing Office / National Archives",
      "licence": "Public domain",
      "url": "https://www.ecfr.gov/api/versioner/v1/full/2026-08-31/title-21.xml",
      "retrieved_at": "2026-09-07T18:25:51.549Z"
    }
  ],
  "citation_policy": "Cite as: Food Additive Index, \"L-Cysteine\", https://foodadditiveindex.com/additives/l-cysteine. This site reports regulatory status and does not rate additives.",
  "generated_at": "2026-09-08T00:09:38.569Z"
}