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The Anatomy of Global Skin Tones
By: Pamela Springer
Posted: June 14, 2012, from the August 2012 issue of GCI Magazine.
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To produce melanin, there has to be two components: an enzyme—tyrosinase, and an amino acid—tyrosine. When these two components go through a conversion process called dopa, melanin is produced. In skin of color, there is increased tyrosinase activity, producing a more concentrated melanin content. The pigment granule’s size is the basis for skin color differences; the darker the skin, the larger the granule.
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.