The skin is the largest organ of the human body and makes up about 15%—roughly seven pounds—of body weight. Its complex, water-resistant structure fulfills numerous protective functions against environmental exposures, such as UV radiation and other harmful toxins; as well as chemical, microbial and physical influences. The nature of the skin’s anatomy limits permeability, which is advantageous as a defense mechanism, but presents a challenge in delivering ingredients into the skin. Topical or transdermal delivery of ingredients are heavily researched for drug applications in the pharmaceutical world, and there are connections and beneficial clinical findings that can be translated for the cosmetic skin care industry, as well. Delivery mechanisms and physiological conditions are identical for both drug and cosmetic ingredients. Therefore, several methods have been examined on how to increase the effectiveness of active ingredients for the skin, and how to overcome the protective barrier, making active ingredients more effective to positively enhance a desired result.
The structure of the skin
Simply put, the skin consists of four main layers:
- The outermost layer, or the stratum corneum (SC);
- The viable epidermis (living tissue);
- The deeper dermal layer; and
- The subcutaneous connective tissue.
The stratum corneum consists of a strong layer of dead skin cells comprised of dehydrated keratinocytes that are embedded in lipid layers. In order to reach living tissue, this protective cover and barrier needs to be passed by active ingredients. Skin care products using active ingredients that cannot pass this barrier can have moisturizing and protective functions, but they cannot affect the living tissue and, therefore, cannot alter or positively influence living cells to achieve a longer-lasting result. How good is an ingredient or product, really, if it can’t reach the area it is intended to reach?