Leucine
Essential branched-chain amino acid. In cosmetics – part of amino acid cocktails for hydration and nourishment of the stratum corneum. Mimics skin NMF (natural moisturizing factor). Safe, but standalone effect on barrier is modest – works as part of a complex.
Evidence by route
Topical application
Part of an amino acid NMF-mimicking complex. Well tolerated, hydration effect is mild and depends on concentration and accompanying amino acids.
- CIR Cosmetic Ingredient Review safety assessment.
How to read tiers A–F
- CWeak evidence. In vitro data, open-label studies, or expert consensus
Tolerability and safety
- Irritation potential
- Low
- Allergen risk
- Low
- Pregnancy
- Safe
- Suitable for
- Normal, Dry, Combination, Oily, Sensitive
About this ingredient
Leucine (L-Leucine) is an essential branched-chain amino acid. In the human body it participates in protein synthesis and activates mTOR signaling in cells. In skin – a component of the natural moisturizing factor (NMF) of the stratum corneum. Mechanism. On skin works as a humectant – attracts moisture. In amino acid complexes restores NMF in deficiency (atopic dermatitis, post-procedure, photoaging). Standalone effect on the barrier is limited; works synergistically with other amino acids and PCA. Where applied. Amino-acid-complex serums and creams (0.1–2%), post-procedure products, recovery masks. Brands include Holika Holika Skin & Good Cera, Esthetic House, La Roche-Posay Toleriane. Evidence base. Direct topical RCTs of leucine are few. Cosmetic effectiveness of amino acid cocktails is proven in NMF complex form (Robinson 2010). CIR confirmed safety. Pregnancy and lactation – safe. Applicable at any stage.
Frequently asked questions
Is Leucine safe during pregnancy?
Leucine is considered safe during pregnancy at typical cosmetic concentrations. Systemic absorption through the skin is minimal.
What skin types is Leucine for?
Leucine suits: normal, dry, combination, oily, sensitive.
What is Leucine and what does it do in cosmetics?
Essential branched-chain amino acid.
What's the INCI name for Leucine?
The INCI name is Leucine. It may also appear as: L-Leucine.
See Leucine in a product composition right on the store page
The Evigrade extension adds an evidence panel to iHerb, Sephora, Druni and 12 more stores. This ingredient and every other one in the product show evidence-tier, allergen risk and pregnancy/lactation flags at a glance.
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