Acetyl Tetrapeptide-9

Acetyl Tetrapeptide-9 is a synthetic signal peptide used mainly for anti-aging/firming benefits, typically at very low concentrations (often well under 1%) in leave-on products. Available clinical and cosmetic safety experience suggests peptides of this class have low inherent irritancy and are generally well tolerated, with occasional stinging or redness more likely driven by the overall formula or compromised barriers rather than the peptide itself. For highly reactive or eczema-prone patients, I still classify it as very gentle (not inert) because any leave-on bioactive can rarely trigger individual intolerance. Safety Notes: In consumer leave-on products (serums, eye creams, neck/firming creams), Acetyl Tetrapeptide-9 is often supplied as a dilute peptide solution and is used at very low active levels; the lowest market-relevant levels are typically around 0.0001% active where it appears near the end of the INCI list in multi-peptide blends. The highest OTC formulations observed generally top out around ~0.01% active (commonly corresponding to ~0.2–2% of a ~0.5% active commercial raw material), reflecting cost, stability, and sensory constraints for peptides in leave-on emulsions; rinse-off usage exists but is usually at the low end due to limited contact time.