Peptides are short chains of amino acids-essentially protein fragments-that improve the skin by mechanisms such as promoting collagen synthesis and repairing the skin barrier. In contrast, hormones are chemical substances that regulate physiological functions; illicitly added hormones in cosmetics (such as glucocorticoids) can lead to dependency or adverse side effects. The two differ fundamentally in their chemical structure and mechanisms of action.
Peptides consist of 2 to 50 amino acids linked by peptide bonds; they have relatively low molecular weights (typically under 5,000 Daltons), allowing them to penetrate the skin's surface layers to exert their effects. Common examples in cosmetics include signal peptides (e.g., Palmitoyl Pentapeptide-4) and carrier peptides (e.g., Copper Tripeptide-1). Their primary functions are stimulating collagen production, providing antioxidant benefits, or soothing the skin, and they possess no hormonal activity.
Hormones are chemical messengers secreted by endocrine glands or cells-such as cortisol or estrogen-that require transport via the bloodstream to act upon target organs.