Methionine

Methionine is a natural amino acid your skin already uses to make proteins and gluthatione (one of the body's key defense molecules against environmental stress like sun + pollution).

Its sulfur content makes it especially reactive with the free radicals that damage skin, giving it genuine antioxidant properties.

Usage percentages are usually under 1%, and usually as part of an amino acid mix designed to mimic what's naturally in skin.

One study used a combination of essential amino acids at 0.2% with supplemental methionine added and found significantly boosted collagen production in human skin.

Cosmetic industry reviewers have looked closely at methionine and other amino acids and found them well tolerated. Methionine is actually used as a "negative control" in lab tests designed to spot irritating ingredients because it doesn't cause a reaction.