Cosmetics have a myriad of ingredients to restore the youthful appearance of skin, but they are best delivered to all skin layers, not just the outermost layer that is visible to the eye. This is especially true for anti-aging cosmetics that help to moisturize skin and support a healthy underlying dermis. The natural protective function of skin inherently makes this a challenge as our skin is effectively a protective waterproof barrier. There is a gradient of hydration with the comparatively dry outermost skin layer at 15-20% water content that increases to 70% several layers beneath. Environmental agents are effectively prevented from penetrating the outermost layer of skin (stratum corneum), which can be likened to a polygonal keratin ‘bricks’ with lipid ‘mortar’ between them. The ability of a cosmetic ingredient to move into these layers of skin depends upon its physical and chemical properties- size, solubility in water or lipid (fat), and electrical charge.  Smaller, less charged molecules that are moderately soluble in both lipid and water will more readily move through skin layers. Small molecules such as amino acids, and vitamins may penetrate skin more readily than larger molecules such as peptides.  

Due to the protective ‘brick-like’ nature of skin, cosmetic ingredients are most likely to stay on the skin surface unless methods are used to promote movement to deeper layers. Some cosmetics contain penetration enhancers such as alcohol, fatty acids or surfactants (soap-like molecules) that disrupt cell membranes of the outermost skin layer, and allow ingredients to more easily move between cells to lower layers of skin. A side effect of this is increased transepidermal water loss (TEWL) and skin irritation, effectively limiting the utility of this strategy. 

To address these limitations, cosmetic formulators have turned to delivery systems that include microscopic lipid bound spherical vesicles with an interior compartment that holds compounds. Liposomes are one example of this approach and have been used to deliver ingredients such as amino acids, antioxidants and vitamins. Liposomes are versatile delivery vehicles. They can either combine with cells or serve as depots to allow a more gradual release of beneficial ingredients into the skin for an extended period of time.

Furthermore,they are an excellent way to enhance skin moisturization since the liposome exterior is often composed of phosphatidylcholine, a natural cell membrane component with a high water binding capacity.  Skin irritation from ingredients such as alpha hydroxy acids can be minimized with liposomal formulations. Liposomes can also enhance formulation capabilities, for example to protect ingredients from oxidation or extend the shelf life of ingredients that are chemically unstable. Due to its comparatively higher formulation cost, liposomal technology is more commonly used in more costly ‘prestige’ cosmetics. Products with liposomes use a sophisticated formulation technology to get the most benefit from anti-aging ingredients.
 
Sources
Badenhorst, T., D. Svirskis and Z. Wu. (2014) Austin Journal of Pharmacology and Therapeutics. Pharmaceutical Strategies for the Topical Dermal Delivery of Peptides/Proteins for Cosmetic and Therapeutic Applications. Austin J Pharmacology Ther  2:10. 
Prausnitz, M.R. et al. (2012) Skin barrier and transdermal drug delivery. In Dermatology (Bolognia, J.L. et al. eds), pp. 2065–2073, Elsevier Health Sciences
 
About the Authors
Annette Tobia, PhD, JD is founder of Dynamis Skin Science, which carries the MEG 21 skin care product line (www.meg21.com), formulated with Supplamine,® an anti-glycation ingredient, which removes age-causing toxic sugar from skin. Dr. Tobia earned her PhD from New York University, completed. post doctoral work at Rockefeller University, and received her law degree from Rutgers School of Law.