Acetyl Tetrapeptide-40

This synthetic peptide is made up of four amino acids designed to calm redness and irritation. It also goes by the name Telangyn.

Your skin has a built-in defense system that fights off bacteria and responds to damage; part of that system involves a natural peptide called LL-37. LL-37 usually does its job and moves on, but sometimes it can go into overdrive (especially in reactive or rosacea skin) and triggers too much inflammation. This is where redness, visible blood vessels, and irritation come from.

That's where Acetyl Tetrapeptide-40 comes in. It turns down the signals that cause this inflammatory overreaction. As a bonus, keeping inflammation in check also protects collagen and other structural proteins from being broken down by enzymes.

According to a manufacturer, this ingredient also calms UV-related inflammation and helps reduce excess pigment production.

This ingredient is considered safe for all skin types and has been shown to work at low concentrations (0.05%).