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Talking Tone: Melanin Under the Microscope
By: Laura J. Goodman
Posted: March 27, 2009, from the April 2009 issue of Skin Inc. magazine.
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Each melanocyte is able to transfer melanin to as many as 30–36 keratinocyte cells via these dendritic extensions. Once inside the keratinocyte cell, the melanin surrounds the nucleus, essentially forming a protective shield against damaging stimuli, such as UV radiation. As the turnover of the epidermis proceeds, the melanin eventually degrades and breaks down, and the cells are sloughed off through the natural process of desquamation—the shedding of the outer layers of the skin.
Genetics determine the ratio and amount of brown-black eumelanins and yellow-red pheomelanins that melanocytes produce on a regular basis. It is the ratio of these melanins that produces natural skin tone. When exposed to UV radiation, the melanocytes are stimulated to produce more melanin than usual, which causes tanning. Additionally, localized overproduction of melanin can be stimulated in the skin by hormone fluctuations, medication, injury, pollution, free radicals and stress.
As people age, cumulative exposure to UV radiation can damage skin cells, and severe damage can cause a melanocyte to be permanently switched on and overproduce melanin. This may result in the formation of solar lentigines, or what are called age or liver spots. Research has shown there are more active melanocytes in chronically sun-exposed skin than in non-exposed skin.4
Shedding light on skin optics and tone
Reflection and refraction of light play a large role in the perception of overall skin tone. About 5% of the light that hits facial skin is reflected off the skin’s surface, while the other 95% penetrates it.5–9 It is this light reflection process that gives human skin its optical depth. The white light passing through skin’s transparent surface reflects off of collagen, which essentially acts as a mirror beneath the surface. As the light reflects back to the surface, it absorbs color from pigments such as melanin and blood within skin’s many layers. Colored light is then diffused softly by the surface, generating a luminous glow.
With aging, collagen becomes more like an antique mirror, and light passes through it, compromising the skin’s ability to reflect and refract light. Additionally, uneven distributions of melanin, or age spots, and hemoglobin, or dilated or broken blood vessels, in the skin can further impede or scatter light, contributing to a dull, less luminous complexion. 5–9 See Figure 2 for an illustrative explanation.