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Leucine

CAS 21675-61-6 · 60/100 · High conf.

Also registered as 4 other CAS numbers

25322-63-8 · 71000-80-1 · 7005-03-0 · 61-90-5

Leucine chemical structure

Concern score

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

Leucine in plain language

What it is

Also known as L-leucine · (2S)-2-amino-4-methylpentanoic acid · Leu · L leucine · (2S)-alpha-2-amino-4-methylvaleric acid · (2S)-alpha-leucine

Show all 20 names

(S)-(+)-Leucine · (S)-2-Amino-4-methylpentanoic acid · (S)-2-Amino-4-methylvaleric acid · (S)-Leucine · 2-amino-4-methylvaleric acid · L-2-Amino-4-methylpentanoic acid · L-Leuzin · L-alpha-Aminoisocaproic acid · L-leucin · Leucin · Leucina · Leucine, L- · Leucinum · alpha-Aminoisocaproic acid

What it does

Used in cosmetics as a skin-conditioning agent, a hair conditioner and an antistatic agent.

  • Skin conditioning
  • Hair conditioning
  • Antistatic
  • Flavouring agent
  • Flavouring
  • Conditioner
Is it a concern?
High concern: no hazard classifications on record. It is listed for cosmetic use in the EU.

Why it's flagged

EPA CPDat observed this chemical in 3 composition records across product categories including Laboratory supplies.

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. Leucine appears in these published regulatory listings.

  • In marketed US drugs
  • Inactive ingredient in US drugs

Recorded in these product areas

  • Found in consumer products
  • Industrial
  • USFDAinactive ingredient database4 entries — 2 administration routes
    • Route: ORAL; Dosage form: TABLET; Maximum daily exposure: 9 mgSource →
    • Route: ORAL; Dosage form: CAPSULE; Maximum daily exposure: 1 mgSource →
    • Route: INTRAVENOUS; Dosage form: INJECTION, SOLUTION; Potency: 0.27 %w/vSource →
    • Route: INTRAVENOUS; Dosage form: INJECTION; Potency: 1.1 %w/vSource →
  • EUEFSAEFSA opinion2 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 →
    • 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 →
  • EUCosIngActiveListed in CosIng inventory for cosmetic use.
    • Listed in CosIng inventory for cosmetic use.Source →
  • 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 3 composition records across product categories including Laboratory supplies. EPA CPDat classifies this chemical for functional uses including Anti-static agent, Softener and conditioner, Flavouring and nutrient.
    • EPA CPDat observed this chemical in 3 composition records across product categories including Laboratory supplies. EPA CPDat classifies this chemical for functional uses including Anti-static agent, Softener and conditioner, Flavouring and nutrient.Source →
  • USFDAmarketed drug occurrenceFDA NDC lists this ingredient in 66 active drug products and 67 total products.
    • FDA NDC lists this ingredient in 66 active drug products and 67 total products.Source →
  • USFDAlisted in openFDA substanceopenFDA substance registry classifies this ingredient as chemical.
    • openFDA substance registry classifies this ingredient as chemical.Source →

Expert safety opinions

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

  • SCCS

    EU Scientific Committee on Consumer Safety

    No SCCS opinion on file.

  • CIR

    Cosmetic Ingredient Review (US expert panel)

    No CIR safety assessment on file.

  • 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 →

    • 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 →

  • 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 →

Evidence & sources

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

10 data sources

Where this comes from

  • CosIng

    regulatory · updated 2026-09-23

    Open →

  • EFSA OpenFoodTox

    regulatory · updated 2026-10-04

    Open →

  • EPA Chemical and Products Database

    exposure · updated February 8, 2019

    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 2027-12-31

    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 →

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 FDA National Drug Code directory has listed Leucine in a product composition. These are source records, not Greenveil catalog products.

Source records

67

Typical roles

Skin conditioningHair conditioningAntistaticFlavouring agentFlavouringConditioner
See products using Leucine →

Catalog

Found in these products

Cosmetic and personal-care products that list Leucine are shown first. Their ingredient lists include Leucine; each product's own rating depends on its whole formula, so it is shown on the product page, not here.

See all 127 →Find products without it →

Co-occurrence

Often appears with

Ingredients that frequently appear alongside Leucine in the catalog.