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How Delivery Systems Change Skin Care Effectiveness
By: Marc A. Ronert, MD, PhD
Posted: June 20, 2014, from the July 2014 issue of GCI Magazine.
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?
As a physician, I often hear the question: “What types of delivery systems are used in order to get ingredients to the spot where they actually can do what they are meant to do?”
The Factors of Functionality
That simple question is extremely complex. There are numerous factors and mechanisms that can promote the delivery of ingredients. The term “delivery system,” as it is used in the skin care industry, refers to the definition or mechanism for how active ingredients reach the deeper layers of the skin in order to fulfill their function at a target site.
There are three mechanisms active ingredients can use to help them reach live tissue.
- Intercellular. These active ingredients travel in between keratinocytes into deeper layers.
- Transcellular. This means that active ingredients must penetrate from cell to cell in order to reach deeper.
- Transappendageal. This means other openings, such as sweat glands, sebaceous glands or hair follicles, are used as travel pathways to reach lower levels of the skin.
The pathway that specific active ingredients can utilize depends on many factors that are closely interconnected.
Concentration. One of the major factors in a good delivery system is the concentration of active ingredients. The higher the concentration of a particular ingredient, the more the skin will try to absorb it, leading to more of the active ingredient ultimately being relocated into the deeper layers of the skin.
pH. Although the concentration is important, it is also influenced by the pH. pH alone is a great delivery system, because the skin is always attempting to neutralize pH differences and stay in a pH-balanced state. The lower the pH, the more product will travel into deeper layers, because the skin is trying to balance and increase the pH again to a higher level. The higher the pH of a particular product, the less the active ingredients will penetrate the skin; instead, they will sit on the surface.