Moisturizers for normal, diseased skin

William Abramovits, M.D., professor of dermatology, Baylor University Medical Center Dallas, presented an overview of these products at the annual Caribbean Dermatology Symposium, here.

"A disturbance of the natural skin barrier function can result in the obvious visual impact of dry skin characterized by the lack of normal luster and the presence of scaling and fissuring," Dr. Abramovits says.

"Compromise of the stratum corneum can result in decreased elasticity, reduced pliability, cracking and scaling of the skin in addition to increased TEWL."

The skin barrier may be altered by diseases such as eczema and psoriasis, genetics or by exogenous factors such as the use of harsh soaps or wind and cold.

Dr. Abramovits discussed both cleansers and moisturizers formulated to preserve and restore the barrier. Ongoing research in his research institute as well as a previous paper published by Dr. Abramovits provided a basis for this presentation: Ceramides and the stratum corneum: structure, function and new methods to promote repair. (Adrian M. Goldstein, M.D., Ph.D. and William Abramovits, M.D., International Journal of Dermatology, 2003, 42, 256-259.)

The skin barrier

"The stratum corneum, the outermost layer of the skin, is composed both of nonviable, protein-enriched corneocytes and a surrounding lipid enriched matrix," Dr. Abramovits says.

The lipids are manufactured in the Golgi apparatus located within the cytoplasm of the keratinocytes. Lipids are stored and later expelled in small vacuoles known as Odland bodies.

"These lipids from the Odland bodies, as well as cholesterol and free fatty acids are dispersed in the skin, and create the natural barrier of protection," Dr. Abramovits says.

Naturally occurring lipids include triglycerides, waxes, fatty acids, squalene, cholesterol esters, glycerides, cholesterol and ceramides.

"The Odland bodies are composed predominantly of lipids, including cholesterol, ceramides and fatty acids," Dr. Abramovits says. All three components are required for skin integrity, he adds, but it is the ceramides that are thought to play an essential role in barrier function.

"Recent research has shown that the ability of keratinocytes to manufacture Odland bodies, also known as lamellar bodies, which may be defective under certain conditions can be corrected by the external application of ceramides, cholesterol and free fatty acids. It has also become clear that there is a critical ratio in which these ingredients have to be present to actually restore the barrier function," Dr. Abramovits says. The ratio in which the products occur naturally in the skin is 3:4:2, for cholesterol, ceramides, and fatty acids, respectively, he adds.

"Disruption of the barrier, either through trauma or certain dermatologic conditions such as atopic dermatitis or eczema, results in compromise of the barrier function," Dr, Abramovits says.

This can result in decreased elasticity, increased susceptibility to infection and increased water loss, he says.

"Treatment with individual components of the stratum corneum, either cholesterol, ceramides or fatty acids alone, or the wrong proportions, may actually delay skin repair," Dr. Abramovits says. A ratio of 3:1:1:1 of cholesterol, ceramide, palmitate and linoleate appears to be critical to restore the natural levels in the skin.

Recent advances in how the barrier functions have led to the development of new products that can preserve and/or restore barrier function.