Tetrapeptide-21 is a chemical compound, a synthetic protein composed of amino acids joined together including:
glutamic acid, glycine and lysine.

It is an abbreviated class of biomolecules and produced by chemical or enzymatic hydrolysis.

Peptides, natural and synthetic, have the ability to activate an immunomodulatory action by interacting with the cells of the immune system.
(Werner GH. Natural and synthetic peptides (other than neuropeptides) endowed with immunomodulating activities. Immunol Lett. 1987 Dec;16(3-4):363-70. doi: 10.1016/0165-2478(87)90170-2. )

What it is used for and where
Cosmetics - INCI Functions
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.
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