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The Three Lines of Skin Defense

By: Sabine Malley, Cliff Milow, Evan Murphy, Kristen Presti, Katherine Spetrino and Zsolt Szabados
Posted: May 29, 2014, from the June 2014 issue of GCI Magazine.

Our skin is exposed to a vast array of harmful influences every day: smog, ozone, dry air and UV rays. These harmful influences attack the skin’s unprotected surface, and with daily exposure comes the danger of extrinsic aging factors, such as free radical oxidation, the breakdown of matrix proteins, DNA damage and the weakening of the skin’s natural barrier, all of which can cause premature aging.

To battle against premature aging, there are three essential lines of protection and correction that are crucial for the maintenance of the skin’s natural beauty. These vital defenses include:

  1. Shielding against UV radiation.
  2. Protecting the skin’s natural lipid structure.
  3. Counteracting internal damage.

1. First Line of Defense—UV Protection

Minimizing the harmful effects of UV radiation is the initial step to building a shield against premature aging. To prevent UV damage, it is imperative to utilize a photostable filter that provides broad spectrum protection, which will deliver uniform coverage across the entire UV light spectrum, including both UVA and UVB rays.

UVB directly affects the intercellular and extracellular components of the skin, leading to sunburn, inflammation and redness. UVA irradiation exerts its detrimental effect predominantly via reactive oxygen species, or ROS, which cause the breakdown of lipids and proteins and leads to DNA damage.

It is necessary to use a combination of both UVA and UVB filters in order to minimize the total amount of UV rays reaching the living layers of the epidermis. In addition to sunburn and other harmful effects caused by intensive UV light, everyday exposure also leads to premature aging of the skin. To overcome this attack both on and in the skin, UV filters can be used in moderate amounts in everyday beauty products (including facial moisturizers, hand creams and body lotions), helping to protect against damage.

Of course, UV filters are not the only ingredients that offer protection. There are other lines of defense that are necessary as well.

2. Second Line of Defense—Barrier Function

Proper skin hydration helps to prevent aging, irritation and damage, and it is essential for healthy looking skin. Key elements include maintenance and strengthening of physiological barrier function, improvement of skin aesthetics, and reduction of dryness and flaking.

Water is the essential component of the skin that determines its softness and flexibility. The factors that influence the skin’s state of hydration are:

  1. The rate at which water reaches the stratum corneum from the layers below;
  2. the ability of the stratum corneum to retain moisture; and
  3. prevention of water leaving the skin through evaporation.

To optimally draw water into the stratum corneum, a synergistic combination of humectants must be determined. Humectants attract moisture to the skin and simultaneously draw moisture up through the skin’s layers. The body contains some naturally occurring humectants that can become depleted due to age, UV exposure or other environmental factors, so it is imperative to add biomimetic humectants to the skin to restore proper moisture flow.

Additionally, natural moisturizing factors—such as sodium hyaluronate, a water-binding polysaccharide—provide a water reservoir within the skin and fill up the space between the skin’s connective fibers. This keeps the extracellular matrix components hydrated and the skin’s structure intact.

The natural skin barrier is composed of intercellular lipids that are assembled in a stacked formation, creating an impermeable barrier for the passage of water and natural moisturizing factors. Complex sugars reinforce the lamellar structure of epidermal lipids, helping to maintain this stacked formation, thereby preventing transepidermal water loss. Skin conditioning agents and film-formers play an essential role in proper barrier function, improving moisture retention and helping prevent the evaporation of water.

3. Third Line of Defense—Normalizing Cellular Processes

Although each layer of the skin contains specific cells, pathways and metabolic activities, they are all interconnected. Consequently, it is imperative to normalize the appropriate cellular processes to protect and maintain dermal organization and the dermal-epidermal junction structure to provide mechanical support for a renewed epidermis.