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The Anatomy of Global Skin Tones
By: Pamela Springer
Posted: May 31, 2012, from the June 2012 issue of Skin Inc. magazine.
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There are two distinct components of melanin. One is constitutive melanin, or pigmentation, and the other is facultative pigmentation. Constitutive pigmentation is the pigment that resides within the keratinocytes and is produced from the body’s own metabolism. Facultative pigmentation is introduced through external stimuli.
The melanocyte is a dendritic cell. The dendrites are tentaclelike projections that enable pigment cells to be deposited into the keratinocyte. These projections are longer in darker skin, enabling pigment granule dispersion into the upper layers of the epidermis.
Another unique difference in darker skin is that pigment granules—also known as melanosomes—are dispersed singularly over the nucleus of the keratinocyte. In Caucasian skin, the granules are considerably smaller and are released in clusters. Racially blended and lighter global skin colors disperse a combination of both single—and clusters of—pigment granules. The activity of a melanosome transfer generally takes place within the lower and upper spinosum layer. In some cases, the transferral is disseminated as pigment droppings into the dermis as a result of injury or trauma to the skin.
The barrier layer of the stratum corneum contains more keratinized dead cell layers in global skin. There is greater intercellular cohesion with a higher lipid content, especially in darker global skin. The stratum corneum is equal in thickness to Caucasian skin; the only difference is that darker global skin has a more compacted stratum corneum, evidenced by its 20 cell layers versus only 16 layers in Caucasian skin. The skin’s permeability, when measured by transepidermal water loss (TEWL), is increased, but it is decreased when exposed to higher temperatures. Also, with increased cellular cohesion, there is normal TEWL, providing an increase in the skin’s water content within its layers.
The dermis in global skin is filled with dense, fibroelastic connective tissue, composed of collagen fibers, elastic fibers and glycosaminoglycans, which are key elements for retaining moisture in the skin. The dermal structure also contains an increased number of fibroblasts that are larger and more active. The increased activity of the fibroblast, the major cell type of the dermis, influences a thicker and more compact dermis. With an increase of fibroblasts, collageneous fibers are more abundant, contributing to a lower incidence of facial wrinkles, especially in Asians and African-Americans. The downside of excessive collagen is the vulnerability to keloids and hypertrophic scarring.