Peptides are portions of proteins, which are long (or sometimes short) chains of amino acids. In the body, peptides regulate the activity of many systems by interacting with target cells. Enzymatic action breaks proteins into peptides so they can exert their influence on the body. Some peptides have hormonal activity, others have immune activity, some are cell-communicating ingredients that tell cells how to react and what to do, some are believed to play a role in wound healing, and still others are believed to affect the pathology of skin conditions such as atopic dermatitis and eczema. All peptides function as "messengers" and in skin care they have cell-communicating ability, assuming the formulation supports the type of peptide used and is packaged to protect it from degrading (no jars!).
Whether peptides have benefit when applied topically to skin for wound healing, skin-barrier repair, or as disinfectants is difficult to ascertain because they generally cannot penetrate skin and at the same time remain stable because they are too hydrophilic, or water-loving. Ironically, peptides can become unstable in water-based formulas (Sources: Biotechniques, July 2002, pages 190–192; and IFSCC Magazine, July 2004, page 153). Further, because peptides are vulnerable to the presence of enzymes, when peptides are absorbed, the abundant enzymes present in skin can break the peptides down to the point where they have no effect at all. However, the latest research is examining how different types of synthesized peptides can enter the living membrane of cells and, more interesting, transport biologically active ingredients to these cells. Some of these peptides have demonstrated a remarkable anti-inflammatory effect. Creating specific peptide chains in the lab and then attaching a fatty acid component to them allows peptides to overcome their inherent limitations: being absorbed and remaining stable. Lab-engineered peptides appear to have the kind of efficacy and benefit that go beyond the skin’s surface, but more conclusive, long-term research is essential to gain an understanding of what, if anything, is really taking place (Sources: Cosmetics & Toiletries, June 2004, page 30; Pharmaceutical Research, March 2004, pages 389–393; and The Journal of Investigative Dermatology, September 2005, pages 473–481). It is reasonable to assume that as synthetic peptide technology broadens, we will see more options for use in skin-care products promoting anti-aging properties, specifically, tissue regeneration (Source: Cosmetics & Toiletries, March 2003, pages 43–52).
For these specialized peptides to exert a benefit beyond that of a water-binding agent, three criteria must be met: the peptides must be stable in their base formula, they must be paired with a carrier that enhances absorption into the skin, and they must be able to reach their target cell groups without breaking down. Achieving this goal is no easy feat, but one that cosmetics scientists are predicting will have significant potential in the realm of anti-aging skin-care ingredients.
Final note: despite claims to the contrary, there are no peptides being used in skin-care products that work like Botox, lasers, or dermal fillers. Peptides also cannot plump lips (at least not to a noticeable extent) nor can they lift sagging skin, lighten dark circles, or eliminate puffy eyes. You'll see all of these claims and more on products with peptides, but they are not supported by published, peer-reviewed research.