Common Name(s): 2-amino-4-(methylthio)butanoic acid,l-met

CAS Number: 63-68-3

DESCRIPTION

What It Does: Provides antioxidant sulfoxide radical scavenging and keratin biosynthesis support.

Why It's Used: Keratin-supporting antioxidant amino acid — methionine's sulfur provides both antioxidant radical scavenging and essential keratin disulfide bond precursor for hair and nail strengthening.

How It Works: Thioether group is oxidised to sulfoxide by ros (sacrificial antioxidant) and reduced back by methionine sulfoxide reductase (catalytic antioxidant cycle). essential for s-adenosylmethionine (sam) methyltransferase activity. keratin cysteine precursor via transsulfuration pathway.

Typically Found In: Antioxidant skin care,nail strengthening,hair care

TECHNICAL DETAILS

Primary Category: Active ingredient – thioether amino acid

Secondary Functions: Skin conditioning

Application Areas:

Typical Concentration Range: 0.5%–5%

SOURCING & ETHICS

Vegan Status: Conditional - supplier confirmation required

Halal Status: Unverified - supplier confirmation required

Source Notes: Commercially produced for cosmetic use. verify vegan/halal status with supplier. [audit 2026-07-29 rev2: the record's own source_notes does not assert a non-animal origin, or instructs the reader to verify with the supplier; "yes" asserts knowledge the record does not hold. determination requires shariah-panel sign-off.]

SKIN COMPATIBILITY

Irritancy Rating: 1/5 – very low

Comedogenicity Rating: 0/5 – non-comedogenic

Sensitivity Concerns: Well-tolerated by most skin types.

Safe for Sensitive Skin: Yes

SAFETY & COMPATIBILITY

Safety Profile: Good safety profile at recommended concentrations. ewg score: 1–2.

Works Well With: Standard skincare actives

Avoid Combining With: No known significant incompatibilities

SCIENTIFIC NOTE

Methionine's sacrificial antioxidant mechanism via oxidation to methionine sulfoxide creates a catalytic antioxidant cycle: methionine is oxidised by ros (scavenging the radical), then methionine sulfoxide reductase (msr) enzymatically reduces it back to methionine using nadph. this cyclic mechanism allows each methionine molecule to scavenge multiple radicals over time — a catalytic rather than stoichiometric antioxidant function.

Last Verified: 2026-03-12

Primary Sources: Cosing database,levine et al. methionine antioxidant cycle study