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What makes dark skin dark and light skin light?

posted 2018 Jul

Tanuj Nakra MD
   
Darker skin is, well, darker than lighter skin. But, why? What is the science behind skin color and why do humans display a wide spectrum of skin tones? It all comes down to genetics and how, over the course of history, humans responded to sun exposure.

This response can be explained through the concept of natural selection - the process by which how organisms respond to their environment over time. Natural selection is often described as “survival of the fittest”; those traits that aid plants and animals to survive their environment, get passed on to their offspring. Over time, evolved species carry these helpful traits.

Just like plants and animals, the various human tribes that populated the earth adapted to their local environments with differences in skin pigmentation. Humans in cold environments had limited sun exposure and required ultraviolet (UV) light to penetrate their skin and produce life-essential Vitamin D. These people had fair skin, to let the UV in.

In contrast, humans in sunny environments had more than adequate UV exposure and efficient, intrinsic Vitamin D production. However, intense and constant UV exposure can damage skin cells and lead to skin cancer. Thus humans in sunny regions adapted to their environment with built-in sun protection: melanin. Melanin is a pigment that exists in all of us and functions as a shield against UV. Our individual melanin content is a marker of our past - the ancestors’ collective need for sun protection.

Now that we understand the evolutionary reasons for dark skin and light skin, let’s explore these differences under the microscope. Under high magnification, we can visualize the pigmented melanin molecule, which is created in specialized skin cells called melanocytes. Melanocytes live in the base layer of the skin and distribute melanin to the other skin cells. Melanin granules then magically arrange themselves into a umbrella configuration above the cell nucleus, protecting each skin cell from UV damage to DNA. Truly a miracle of our biology!

Equal amounts of melanin are present in all humans, no matter how light or dark the skin. It’s simply the subtype of melanin that differs in light skin versus dark skin. Because the melanin in darker skin is, well, darker, issues with the melanin pathway become much more visible. We’re talking about pigment irregularity or melasma (brown spots and patches). However, even light-skinned people have melanin pathway irregularities, often described as uneven skin tone.

Beyond melanin, there are challenges that more pigmented people face. In comparison to lighter skin, dark skin has larger sebaceous glands - the oil-producing glands of the skin. Many darker-skinned people can have issues with their sebaceous glands like large pores, oiliness, and acne. Darker skin also has an increased desquamation or tendency to shed its outer layers, which can lead to scaling and an ashy appearance.

The good news for pigmented skin? It's thicker than light skin, so with aging, dark skinned people tend to have less wrinkles in comparison to lighter skin. This is due to a higher number of fibroblasts in dark skin. These are the cells that produce collagen and play a critical role in wound-healing. In addition, there are more lipids (intrinsic skin fats) in darker skin, leading to increased water retention and thickness. This leads to better skin tone.

The wealth of scientific information about skin diversity can be harnessed to create skincare products specifically for darker skin. Products designed by and developed for darker-skinned people are exceedingly rare, especially in the luxury, high-efficacy marketplace. We at AVYA Skincare have spent years researching, analyzing and formulating our products to focus on all aspects of dark skin: the melanin pathway, sebaceous glands, desquamation, fibroblasts, and intrinsic lipids. As the scientist in charge of AVYA’s research and development, I’m passionate about all the beautiful, shades of brown skin. We live in a very exciting time: youthful, radiant skin is truly possible for all.