SKINIPEDIA - Skin Encyclopedia: The Dry Skin

The Dry Skin: It's a Sure Thing

by Diana L. Howard, Ph.D.

THERE ARE VERY FEW GUARANTEES IN LIFE. Reading glasses by the time you’re 42 is almost a sure bet. And now we can pretty much expect dry skin by 40 as well—at least that’s the conclusion of scientists who have studied the lipids of the epidermis. The sharp decline in the stratum corneum lipids that occurs as we age—especially the significant drop in ceramides, one of the more important structural components of the lipid barrier—has led scientists to conclude that by the time we reach 40, our skin will almost certainly be dry and/or dehydrated.

Unfortunately, not everyone has the good fortune of waiting until they are in their 40s to deal with a dry skin
condition. As a matter of fact, a recent survey of women over 18 indicated that 59 percent of those polled felt dry,
dehydrated skin was their No. 1 skin care concern; this was followed by 52 percent who ranked wrinkles as their
top priority. Continuous exposure to the sun, wind and chemicals in the environment, not to mention a stressful
lifestyle—all of which are contributing factors for dry, dehydrated skin—make this a legitimate concern for people of all ages.

What is dry, dehydrated skin?

Dry, or alipoid skin, generally refers to skin that is lacking oil, whereas dehydrated skin lacks moisture in the stratum corneum, the outermost layer of the epidermis.

Contrary to popular belief, dehydrated skin may also look soft and smooth; this is often the case when sebum, the skin’s natural oil, conceals dry scales. There is a widespread misconception that dehydrated is the opposite of oiliness, but “dehydrated” refers to lack of moisture not oiliness. Again, “dry” refers to levels of sebum or oil on the skin.

While adequate sebum does help maintain water levels in skin, oily skin can also be dehydrated. Dehydrated skin may lack water only in the outermost layers of the epidermis but may have normal levels of moisture in the deeper layers. Typically, cells that comprise the deepest layers of the epidermis have about 80-percent water content, whereas cells of the
stratum corneum are about 10 percent water; anything below 10 percent is perceived as dehydrated. This dehydration may manifest itself in the form of dry, scaly superficial cells and in extreme cases, the stratum corneum will be thicker with microscopic fissures.

When skin is both dry and dehydrated, it is often irritated, inflamed and itchy and it is generally worse in areas with relatively few sebaceous (oil) glands such as arms, legs and torso.

Also, the notion that drinking your full daily ration of water helps with these conditions is a misconception as well. Water may not really help with dry or dehydrated skin. Of course drinking adequate water is critical to maintain other physiological processes, but it most likely will not help dry, dehydrated skin.

When we see a skin condition with scaly, dry cells on the surface, this may be the result of dehydrated tissues, loss of lipids in the stratum corneum and/or an abnormality with the desmosomal structures, the attachment sites whereby one stratum corneum cell attaches to an adjacent cell. Scientists have recently discovered that an excess of cells on
the skin’s surface may actually be the result of malfunctioning enzymes responsible for desmosome digestion; a lack of water may affect enzyme activity preventing normal desquamation from occurring. The result is an accumulation of cell clumps that cause the skin to appear rough and dry.

 

 

The two major components of the stratum corneum that allow it to control TEWL are the natural moisturizing factor (NMF) and the lipids. The NMF is a complex mixture of water-soluble compounds that have the ability to bind water against the desiccating action of the environment. It is made up of amino acids, urea, PCA, lactic acid, sugars, peptides,
etc. Because these chemicals are hydrophilic, they help hold large amounts of water in the skin cells. The NMF also provides an important aqueous environment for enzymes of the stratum corneum. The importance of the
NMF is very apparent when one considers the skin condition ichthyosis vulgaris, whereby patients lack an NMF and display severe dehydration and skin scaling. Normal skin, when exposed to harsh cleansers such as soap, will also display reduced levels of NMF as does the skin of elderly patients. It is no surprise that all of the components of the NMF make excellent humectants when formulated into a moisturizing skin care product.


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