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Cysteine

CAS 52-90-4 · 60/100 · High conf.

Also registered as 4 other CAS numbers

202114-66-7 · 4371-52-2 · 154605-72-8 · 1404190-35-7

Cysteine chemical structure

Concern score

60/100High concern based on regulatory listings.
High confidence

Cysteine in plain language

What it is

Also known as L-cysteine · L-(+)-Cysteine · (2R)-2-amino-3-sulfanylpropanoic acid · L-2-AMINO-3-MERCAPTOPROPIONIC acid · (R)-2-Amino-3-mercaptopropanoic acid · (R)-2-Amino-3-sulfanylpropanoic acid

Show all 24 names

(R)-Cysteine · 2-Amino-3-mercaptopropionic acid · Cysteine, l-(+)- · Cystein · Cysteine, L- · E 920 · Free cysteine · Half-cystine · L-Alanine, 3-mercapto- · L-Cys · L-Cystein · R-2-AMINO-3-MERCAPTOPROPIONIC acid · Thioserine · alpha-Amino-beta-thiolpropionic acid · beta-Mercaptoalanine · cisteina · Cysteinum · Cisteinum

What it does

Used in food as a flavouring agent.

  • Flavouring agent
  • Preservative
  • Flavouring
Is it a concern?
High concern: no hazard classifications on record.

Why it's flagged

EPA CPDat observed this chemical in 45 composition records across product categories including Personal care.

The score describes this ingredient's chemical identity — its hazard profile from published classifications and regulatory status — not the safety of any product it appears in.

Regulation

No restrictions found. Cysteine appears in these published regulatory listings.

  • In marketed US drugs
  • Inactive ingredient in US drugs

Recorded in these product areas

  • Found in consumer products
  • Beauty
  • Cleaning
  • EUEFSAEFSA opinion3 entries
    • Scientific Opinion on the safety and efficacy of the use of amino acids (chemical group 34) when used as flavourings for all animal species (EFSA FEEDAP)Source →
    • Opinion of the Scientific Panel on Food Additives, Flavourings, Processing Aids and Materials in Contact with Food on a request from the Commission related to the use of L-cysteine in foods intended for infants and young children (EFSA AFC)Source →
    • Flavouring Group Evaluation 79, (FGE.79). Consideration of amino acids and related substances evaluated by JECFA (63rd meeting) structurally related to amino acids from chemical group 34 evaluated by EFSA in FGE.26Rev1 (2008). Scientific Opinion of the Panel on Food Additives, Flavourings, Processing Aids and Materials in Contact with Food (EFSA AFC)Source →
  • USFDAinactive ingredient database2 entries
    • Route: INTRAVENOUS; Dosage form: SOLUTION; Potency: 0.01 %w/vSource →
    • Route: INTRAVENOUS; Dosage form: INJECTION, SOLUTION; Potency: 0.02 %w/vSource →
  • GLOBALJECFANo safety concern at current levels of intake when used as a flavouring agentJECFA evaluation lists ADI No safety concern at current levels of intake when used as a flavouring agent. Functional class: flavouring agent.
    • JECFA evaluation lists ADI No safety concern at current levels of intake when used as a flavouring agent. Functional class: flavouring agent.Source →
  • USEPAcommercial use observedEPA CPDat observed this chemical in 45 composition records across product categories including Personal care. EPA CPDat classifies this chemical for functional uses including Flavouring and nutrient, Processing aids not otherwise specified, Filler.
    • EPA CPDat observed this chemical in 45 composition records across product categories including Personal care. EPA CPDat classifies this chemical for functional uses including Flavouring and nutrient, Processing aids not otherwise specified, Filler.Source →
  • USFDAlisted in openFDA substanceopenFDA substance registry classifies this ingredient as chemical.
    • openFDA substance registry classifies this ingredient as chemical.Source →
  • USFDAmarketed drug occurrenceFDA NDC lists this ingredient in 25 active drug products and 34 total products.
    • FDA NDC lists this ingredient in 25 active drug products and 34 total products.Source →

Expert safety opinions

Independent scientific assessments cited by the records we hold, with the year and link where the record gives one.

  • JECFA

    Joint FAO/WHO Expert Committee on Food Additives

    • JECFA evaluation lists ADI No safety concern at current levels of intake when used as a flavouring agent. Functional class: flavouring agent.

      Year not recorded · GLOBAL JECFA listing · Read the source →

  • EFSA

    European Food Safety Authority

    • Scientific Opinion on the safety and efficacy of the use of amino acids (chemical group 34) when used as flavourings for all animal species (EFSA FEEDAP)

      2014 · EU EFSA listing · Read the source →

    • Opinion of the Scientific Panel on Food Additives, Flavourings, Processing Aids and Materials in Contact with Food on a request from the Commission related to the use of L-cysteine in foods intended for infants and young children (EFSA AFC)

      2006 · EU EFSA listing · Read the source →

    • Flavouring Group Evaluation 79, (FGE.79). Consideration of amino acids and related substances evaluated by JECFA (63rd meeting) structurally related to amino acids from chemical group 34 evaluated by EFSA in FGE.26Rev1 (2008). Scientific Opinion of the Panel on Food Additives, Flavourings, Processing Aids and Materials in Contact with Food (EFSA AFC)

      2008 · EU EFSA listing · Read the source →

Evidence & sources

No graded research studies for Cysteine yet. This record is compiled from the published data sources below — registries and regulatory listings, not study findings.

9 data sources

Where this comes from

  • EFSA OpenFoodTox

    regulatory · updated 2026-10-04

    Open →

  • EPA Chemical and Products Database

    exposure · updated September 2018

    Open →

  • EPA DSSTox Identifiers

    chemistry · updated 2025-12-29

    Open →

  • FDA Inactive Ingredient Database

    regulatory · updated 2026-01-09

    Open →

  • FDA National Drug Code Directory

    regulatory · updated 2029-06-13

    Open →

  • FDA GSRS UNII

    registry · updated 2026-02-26

    Open →

  • WHO JECFA Database

    regulatory · updated 2026-10-04

    Open →

  • openFDA Substance

    registry · updated 2026-05-24

    Open →

  • PubChem Live Enrichment

    chemistry · updated 2026-05-17

    Open →
Reference links (1)

Suitability

Context-specific fit derived from published classifications and the current ingredient evidence profile.

Food use

Food-use source coverage is present in the current record.

Good fit

The ingredient appears in food-oriented source coverage or allowed-use references, which makes food use easier to support than a context with no domain signal at all.

Fragrance avoidance

No fragrance-linked caution surfaced in the current profile.

Good fit

This ingredient does not currently read as a fragrance-linked driver in the published evidence and hazard profile.

Where it has been recorded

How often EPA CPDat has listed Cysteine in a product composition. These are source records, not Greenveil catalog products.

Source records

45

Named organisations

6

Personal care

Typical roles

Flavouring agentPreservativeFlavouring
See products using Cysteine →

Catalog

Found in these products

Their ingredient lists include Cysteine; each product's own rating depends on its whole formula, so it is shown on the product page, not here.

See all 45 →Find products without it →