SKINIPEDIA - Skin Encyclopedia: The Dry Skin

The Dry Skin: It's a Sure Thing (Part 4)

by Diana L. Howard, Ph.D.

Emollients and occlusives are combined with humectants (molecules that act as water magnets) to help hydrate the layers of the skin. Some of the more popular humectants that are used in moisturizers include honey, lactic acid, PCA, propylene glycol, amino acids, panthenol, glycerin and last, but not least, the most effective humectant, hyaluronic acid. Often referred to as sodium hyaluronate or hyaluronan, this unique glycosaminoglycan (often abbreviated GAG) is found naturally in the cellular matrix of the dermis. Hyaluronic acid can hold a thousand times its weight in water, which helps keep the
skin tissues well hydrated. Why is this beneficial? Because the water-logged GAGs surround the collagen and elastin
fibers of the dermis and keeps them pliable, ensuring the dermis has optimal turgor and elasticity. Think of a dry
sponge sitting on the kitchen counter. When it is dry, you can knock it against the counter and hear how hard and
feel how brittle it is; but once it is hydrated, the sponge becomes soft and elastic.

 

 

Scientists have found that there is a direct correlation between the amount of hyaluronic acid and the water content of dermal tissue. As skin ages and matures, a decline in hyaluronic acid also occurs. The most dramatic change is seen after the age of 50, which coincides with a deterioration in the mechanical properties of skin, including a loss of elasticity in the intercellular matrix. Studies indicate that to increase the moisture content of skin, you must increase the level and length of time that hyaluronic acid is present in the skin, as well as, preserve the chain length of this sugar polymer. In this regard, ingredients like grapeseed extract, which inhibit the enzyme (hyaluronidase) that breaks down the hyaluronic
acid chains, would help maintain the chain length of this important hydration molecule.

How do moisturizers benefit skin?

While emollients, occlusives and humectants are critical components of a moisturizer, a well-formulated product should help restore the barrier layer of the skin. This is the invisible lipid barrier in the outermost layers of the epidermis that helps trap moisture in the deeper layers of the skin and therefore, reduces transepidermal water loss (TEWL) from the skin. It also helps keep environmental sensitized skin, which is more reactive to anything that touches the skin, may result from a compromised barrier layer. When the barrier layer is stripped from our skin, we lose moisture from the deeper layers, leading to a dehydrated skin. What are the biggest culprits that remove this barrier layer? Very simply: soap and water, overexfoliation and exposure to harsh chemicals, which can include skin care products! Anything with a high pH like soap will literally strip the barrier lipids from our skin—your clients might comment on that taut, well-cleansed feeling that they get after using soap and water or even a cleanser that is too harsh for the skin. Ingredients that help restore the barrier layer of our skin include silicones, ceramides, olive oil, essential fatty acids, such as linoleic acid, tocopherol (vitamin E) and other lipid substrates.

The array of ingredients that are available for use in moisturizers today is indeed extensive. There are emollient
ingredients to improve skin smoothness, occlusives to help retard water loss and humectants to help hydrate.
Varying concentrations of emollients, occlusives and humectants will be found in formulations, depending on
the skin condition the product is designed to treat. A proper skin analysis will help you prescribe the correct
moisturizer for your clients. Regardless of what skin condition you are treating, spray a hydrating (water or
botanical extract based—no alcohol!) toner on the skin after cleansing, followed with a moisturizer. Studies have
shown that to maximize the benefits of a moisturizer, it should be applied within two minutes after cleansing the
skin. The longer you wait, the less benefits it provides. While normal physiological processes and exposure to
a dynamic environment may all contribute to dry skin, fortunately for us, with the vast array of humectants and
technology that cosmetic chemists now have at their disposal, dry skin may not be such a sure thing after all.

The author of this article, Diana L. Howard, Ph.D., has more than 25 years of experience in cosmetic research and product development. Her doctorate in biochemistry is from UCLA. She is the vice president of technical development for
Dermalogica and The International Dermal Institute.