Phenylalanine

What is Phenylalanine?

Phenylalanine is one of the amino acids your body uses to build proteins. Cosmetic phenylalanine is usually made by fermentation or chemical synthesis, and the label name doesn’t tell you which.

Phenylalanine has a ring-shaped side chain, which makes it one of the more oil-loving amino acids. In skincare it almost always appears as part of a longer list of amino acids rather than on its own.

On a label it usually sits in a group with other amino acids, such as glycine, alanine, serine, proline and aspartic acid. You’ll find it in serums, toners, moisturizers and some hair products.

What does Phenylalanine do?

• Conditions skin. The safety review describes amino acids as working mainly as skin and hair conditioning agents.
• Helps hold water. Amino acids are also listed as humectants, so they help a product hold moisture at the skin’s surface.
• Rounds out a blend. Alongside other amino acids and humectants, it adds to a soft, hydrated finish.

It’s a supporting ingredient. The safety review reported it at no more than about 0.03% in cosmetics, so it isn’t a reason to buy a product on its own.

Who is Phenylalanine for?

It suits most skin types, including dry and sensitive skin. The safety panel reviewed alpha-amino acids as a group and concluded they are safe as used in cosmetics.

The “acid” in “amino acid” sometimes worries people with sensitive skin. Phenylalanine isn’t an exfoliating acid. If a product that lists it stings, other ingredients in the formula, such as fragrance or an exfoliating acid, are more likely to be responsible. Patch-test new products if your skin reacts easily.

What to pair Phenylalanine with, and what to avoid

It already sits alongside other amino acids and humectants such as glycerin and hyaluronic acid in most formulas. There’s nothing you need to avoid with it, and you don’t need a separate phenylalanine product.