What it is
Cysteine is a naturally occurring amino acid distinguished by a reactive thiol (sulfur) group, which underlies its antioxidant behavior. In cosmetic formulations it is used as a skin-conditioning and antioxidant agent and can also play a role in hair-care chemistry due to its sulfur content. It is water-soluble and incorporated at low levels in skincare and sun-care products.
Safety & warnings
As a naturally occurring amino acid, cysteine is generally well tolerated on skin at cosmetic use levels and is not associated with comedogenicity.
Origin & sourcing
Cysteine is a standard proteinogenic amino acid; cosmetic-grade material may be obtained from protein hydrolysates or produced by fermentation or synthesis.
Questions everyone asks
What is cysteine?
It is a sulfur-containing amino acid used in skincare as a skin-conditioning and antioxidant ingredient.
Why is cysteine an antioxidant?
Its reactive thiol (sulfur) group lets it help neutralize reactive species, which is the basis of its antioxidant role.