Occlusives, humectants, and emollients treat the symptoms of dry skin, while barrier repair ingredients treat the causes of dry skin.
Hyaluronic and oleic acids increase penetration of other ingredients.
The type of water used in a moisturizer can affect its efficacy.
Using the wrong ratio of ceramides, fatty acids, and cholesterol will injure the skin barrier and worsen dehydration.
Unsaturated fatty acids decrease melanin synthesis and tyrosinase activity, while saturated fatty acids increase melanin synthesis and tyrosinase activity.
Barrier repair moisturizers can diminish inflammation and reduce inflammatory cytokine levels in serum.
New technologies to increase penetration using nanotechnology and other methods will increase the ability to add ingredients to moisturizers.
Moisturization research was spearheaded in the 1950s when Blank demonstrated that low moisture content of the skin is a prime factor in dry skin conditions.1 In the last 50 years, scores of scientists have devoted their lives to researching moisturization and have begun to unravel the mysteries of skin hydration (see Chapter 12, Dry Skin). It is now known that the symptoms of dry skin can be treated by increasing the hydration state of the stratum corneum (SC) with occlusive or humectant ingredients and by smoothing the rough surface with an emollient. Moisturizers represent a multibillion-dollar market in the United States. Commonly used moisturizers are oil-in-water emulsions and water-in-oil emulsions. In some cases, oils are used as a moisturizer. This chapter will identify and discuss the mechanisms of action of the main components found in popular moisturizers.
MECHANISM OF ACTION OF MOISTURIZERS
There are numerous moisturizers on the market but they all have the same goal: to increase water content in the SC. This can be accomplished by preventing water evaporation from the skin through the use of occlusive ingredients or by augmenting the integrity of the skin barrier (see Chapter 12). The mainstay of enhancing the skin barrier’s integrity involves providing fatty acids, ceramides, and cholesterol in moisturizers. Ensuring a healthy skin barrier is the best way to combat skin dehydration.
Improving the skin’s ability to hold on to water is another strategy for moisturizing skin. Increasing levels of natural moisturizing factor (NMF), glycerin (glycerol), and other humectants such as hyaluronic acid (HA) and heparan sulfate (HS) will help skin retain water. Lastly, increasing the ability of the epidermis to absorb important components for the circulation, such as glycerol and water through aquaporin (AQP) channels, will also aid in increasing skin hydration.
Moisturizers play a larger role than just hydrating the skin. They can affect the calcium gradient, pH, and fatty acid distribution of the skin. Moisturizers can also influence mRNA expression of genes such as involucrin, transglutaminase, and kallikrein. In addition, they can modify keratinocyte differentiation and desquamation.2
Moisturizers also affect skin penetration. If they are placed ...