Acetyl tetrapeptide-5 is a synthetic chain of four amino acids, developed specifically for the under-eye area. Two proposed mechanisms are usually cited, and they address different causes of the same visible problem.
Fluid accumulation
Under-eye puffiness frequently involves fluid pooling in the tissue, which drains poorly in an area with limited lymphatic flow and very thin skin.
Acetyl tetrapeptide-5 is proposed to influence vascular permeability, reducing how readily fluid leaks from capillaries into surrounding tissue. Less leakage means less accumulation.
Glycation
The second mechanism is more interesting and less commonly explained.
Glycation is a reaction in which sugars bind to proteins without enzymatic control, producing advanced glycation end products. When this happens to collagen and elastin, the fibres become cross-linked and stiffer, losing the flexibility that lets skin recover its shape.
Acetyl tetrapeptide-5 is studied as an anti-glycation agent, proposed to interfere with that cross-linking. Since glycation accumulates over decades and is not readily reversed, prevention is the realistic framing rather than repair.
The evidence
Both mechanisms come largely from manufacturer research, which is the norm for cosmetic peptides and worth stating rather than glossing over. Independent replication is limited.
The delivery question applies here as it does to all peptides: acetyl tetrapeptide-5 is water-soluble and the stratum corneum is structured to exclude such molecules. Being a tetrapeptide, it is small by peptide standards, which helps, and the acetyl group increases lipophilicity slightly, which also helps. Neither settles the question.
In formulation
Used at low concentrations, almost always in eye products, and typically alongside other peptides and circulation-focused ingredients rather than alone.
