Phenylalanine
Essential aromatic amino acid, body precursor of tyrosine and melanin. In cosmetics part of amino acid complexes as an NMF component. Systemic studies show that phenylalanine combined with UV can stimulate repigmentation in vitiligo; topically this effect is not clinically confirmed.
Evidence by route
Topical application
Safe at cosmetic concentrations. Effect – contribution to the overall NMF amino acid pool, without notable standalone activity on skin.
- 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
Phenylalanine (L-Phenylalanine) is an essential aromatic amino acid. In the body it serves as a precursor of tyrosine and downstream melanin, as well as dopamine, norepinephrine and epinephrine. Where applied. Serums, toners, creams with amino-acid complexes as part of NMF (natural moisturising factor) – at 0.01-0.5%. Marketed as a "nourishing amino acid for skin". Evidence base. Oral L-phenylalanine with UVA exposure is studied for vitiligo: studies (Antoniou 1989, Cormane 1985) showed repigmentation in 25-60% of patients with localised vitiligo. This effect is oral + UVA, unrelated to topical cosmetics. No topical RCTs of phenylalanine alone on skin. Safety. CIR confirmed safety at cosmetic concentrations. Hypoallergenic. Non-comedogenic. Minimal systemic absorption through intact skin. Patients with phenylketonuria (PKU) avoid phenylalanine systemically; the topical concentration in cosmetics (microquantity) is not considered a significant exposure even in PKU. Pregnancy and lactation – topical form is safe. Suitable in any product.
Frequently asked questions
Is Phenylalanine safe during pregnancy?
Phenylalanine is considered safe during pregnancy at typical cosmetic concentrations. Systemic absorption through the skin is minimal.
What skin types is Phenylalanine for?
Phenylalanine suits: normal, dry, combination, oily, sensitive.
What is Phenylalanine and what does it do in cosmetics?
Essential aromatic amino acid, body precursor of tyrosine and melanin.
What's the INCI name for Phenylalanine?
The INCI name is Phenylalanine. It may also appear as: L-Phenylalanine.
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