Phenylalanine is a useful amino acid for the human body, but it is not synthesized by the body so it is necessary to take a certain amount from foods that contain a lot of proteins.

What it is used for and where

It is an α-amino acid.

Amino acids play a key metabolic function in the human body and are constituents of proteins. 

As food additives they perform different functions: preservatives, flavour enhancers, food supplements and more.

Amino acids together with their salts are used in cosmetics as conditioning agents for both hair and skin (e.g. as moisturisers and other similar functions). Moisturisers are different in nature: the best are the natural ones that exploit the mechanism of integration between the ingredient and the skin by moisturising the horny hydrolipid film, i.e. the thin protective layer that covers the epidermis protecting it from harmful external microbes, keeping the skin moisturised and supple and its pH or acidity value between 4 and 6.  Then there are the occlusive moisturisers, usually derived from petroleum (Paraffinum, Paraffinum liquidum and others), but also triglycerides, lanolin oil, natural or synthetic waxes, fatty acid esters and others that create an artificial occlusive layer on the stratum corneum of the skin with the advantage of accelerating the protective process but with the disadvantage of preventing the skin's natural transpiration.

α-amino acids that have similar physical structures undergo similar changes with regard to solubility in water/ethanol mixtures, and technologies to separate α-amino acids from industrial residues, which may not even be innocuous, are constantly being improved. However, many data on the solubility in water-ethanol and ethanol of some α-amino acids are contradictory or even lacking, and the effects of ethanol on the solubility of amino acids may be different. Overall, the scientific literature considers that α-amino acids do not pose significant problems for human health when taken orally, except in people with certain genetic diseases.

Food safety: amino acid α generally considered safe.

Cosmetic safety: amino acid α generally considered safe when formulated to be non-irritant.

Medicine

A deficiency of phenylalanine can lead to depression.

In medicine a compound called DLPA is used which is known as DL-Phenylalanine is that it has the ability to mitigate chronic pain and depression by starting endorphins. Endorphins are neurotransmitters found in the brain and in practice act as natural painkillers.

Cosmetics

Incorporated into topical creams, it helps transform pigment-forming melanocytes by aiding skin exfoliation and the removal of dead or replacement cells.

INCI Functions

• Hair conditioning agent. A significant number of ingredients with specific and targeted purposes may co-exist in hair shampoo formulations: cleansers, conditioners, thickeners, matting agents, sequestering agents, fragrances, preservatives, special additives. However, the indispensable ingredients are the cleansers and conditioners as they are necessary and sufficient for hair cleansing and manageability. The others act as commercial and non-essential auxiliaries such as: appearance, fragrance, colouring, etc. Hair conditioning agents have the task of increasing shine, manageability and volume, and reducing static electricity, especially after treatments such as colouring, ironing, waving, drying and brushing. They are, in practice, dispersants that may contain cationic surfactants, thickeners, emollients, polymers. The typology of hair conditioning agents includes: intensive conditioners, instant conditioners, thickening conditioners, drying conditioners. They can perform their task generally accompanied by other different ingredients.
• Fragrance. It plays a very important role in the formulation of cosmetic products as it provides the possibility of enhancing, masking or adding fragrance to the final product, increasing its marketability. It is able to create a perceptible pleasant odour, masking a bad smell. The consumer always expects to find a pleasant or distinctive scent in a cosmetic product. 
• Skin conditioning agent. It is the mainstay of topical skin treatment as it has the function of restoring, increasing or improving skin tolerance to external factors, including melanocyte tolerance. The most important function of the conditioning agent is to prevent skin dehydration, but the subject is rather complex and involves emollients and humectants that can be added in the formulation.

 The most relevant studies on this ingredient have been selected with a summary of their contents:

Phenylalanine studies

• Molecular Formula: C₉H₁₁NO₂
• Linear Formula C₆H₅CH₂CH(NH₂)CO₂H
• Molecular Weight: 165.192 g/mol
• UNII: 47E5O17Y3R
• CAS: 63-91-2  62056-68-2
• EC Number: 200-568-1
• FEMA Number: 3585
• PubChem Substance ID 329820075
• MDL number MFCD00064227
• Beilstein Registry Number 1910408

Synonyms:

• L-phenylalanine
• phenylalanine
• Phenylanine
• (2S)-2-amino-3-phenylpropanoic acid
• (S)-2-Amino-3-phenylpropanoic acid
• 3-Phenyl-L-alanine
• (S)-Phenylalanine
• (S)-alpha-Aminohydrocinnamic acid
• Alanine, phenyl-, L-
• (S)-(-)-Phenylalanine
• beta-Phenylalnine, (-)-
• (S)-alpha-Amino-benzenepropanoic acid
• Phenylalanine, L-
• Hydrocinnamic acid, alpha-amino-
• 2-Amino-3-phenylpropionic acid, L-
• (S)-2-Amino-3-phenylpropionic acid
• beta-Phenyl-L-alanine
• (L)-Phenylalanine
• 3-Phenylalanine