Skin color is the first thing you see when you see someone. Skin color has many uses, and the color of one’s skin can give you a general idea of the type of climate one’s ancestors evolved in. The lighter one’s skin is may tell you that their ancestors evolved in low UVB radiation, whereas the darker one’s skin is may tell you that their ancestors evolved in high UVB places. So this tells us that as migration occurred out of Africa, skin needed to lighten in order to synthesize vitamin D in low UVB climes. Note that I won’t make any claims about any skin color being an adaptation to any climate; I will just state that there is a strong association between UVB and skin color—the higher the UVB the darker the skin and the lower the UVB the lighter the skin.
The skin comprises about 16 percent of the human body, making it the body’s largest organ (D’Orazio et al, 2013). There are two layers to the skin, the dermis and epidermis. The outermost layer of skin—the epidermis—is the point of contact with the environment. So since this is the case, then the number of UVB rays in any given environment will dictate the color of one’s skin—in an ancestral manner.
So the most important factor in skin color is melanin, which is produced by melanocytes, but it accumulates in the keratinocytes of the stratum basale (the deepest layer of the five layers of the epidermis) and the stratum spinosum (the layer between the stratum granulosum and the stratum basale). Two forms of melanin exist: eumelanin (which is brownish black) and pheomelanin (which is reddish-yellow and contains sulfur).
In his textbook Anatomy and Physiology: The Unity of Form and Function, professor Ken Saladin writes:
People of different skin colors have essentially the same number of melanocytes, but in dark-skinned people, the melanocytes produce greater quantities of melanin, the melanin granules in the keratanocytes are more spread out than tightly clumped, and the melanin breaks down more slowly. Thus, melanized cells may be seen throughout the epidermis, from stratum basale to stratum corneum. In light-skinned people, the melanin is clumped near the keratinocyte nucleus, so it imparts less color to the cells. It also breaks down more rapidly, so little of it is seen beyond the stratum basale, if even there.
The amount of melanin in the skin also varies with exposure to ultraviolet (UV) rays of sunlight, which stimulates melanin synthesis and darken the skin. A sun-tan fades as melanin is degraded in older keratinocytes and as the keratinocytes migrate to the surface and exfoliate. (Saladin, 2010: 194)
Skin color is one of the most significant factors involved in colonizing a certain, new, area where the skin color the group has is not conducive to life in that clime. So, when the out of Africa migration occurred, skin color needed to lighten as to better confer survival in the new, colder climes. Though, there is an anomaly: Arctic peoples. Why is their skin dark—at least relative to other peoples who live or have lived in colder climates?
Think about life in the Arctic. It is pretty much all white. Food is scarce, and they eat a lot of animal fat and protein. Now, think about the ice. The ice reflects UV rays onto the skin of the Arctic people, making it not as light as, say, Europeans and East Asians.
A term I’ve heard a lot over the years is “Black don’t crack”, speaking to the fact that a lot of black people look young, even into old age. What, if any, is the physiologic reason behind this? For instance, Vashi, Maymone, and Kundu (2016) write:
Individuals with darker skin are overall thought to have firmer and smoother skin than individuals with lighter skin of the same age
Rawlings (2006) states that “Caucasians have an earlier onset and greater skin wrinkling and sagging signs than other skin types and in general increased pigmentary problems are seen in skin of colour although one large study reported that East Asians living in the U.S.A. had the least pigment spots.” Blacks have more corneosome layers than whites (21.8 cell layers compared to 16.7 cell layers). There is no difference in skin thickness between whites and blacks, so black skin is thought to be more compact with greater intercellular cohesion (see also La Ruche and Cesarini, 1992). Take transepidermal water loss (TEWL)—the total amount of water vapor lost through the skin and other appendages through non-sweating conditions. Since the Asian corneum is thinner, it takes fewer tape strippings to decrease TEWL compared to blacks who take more tape strippings, while whites are in the middle. (Though some studies note no difference).
Rawlins (2006: 85) notes that Sugino, Imokawa, and Maibach (1993) state that TEWL is greater in the order of Blacks > Caucasians > Hispanics > Asians.
So why does it seem that blacks, on average, age less than whites in the fact? I can think of one main thing: Their darker skin protects them from the effects of photoaging due to the melanocytes their skin produces. The opposite holds for whites—white skin produces fewer melanocytes and therefore is less protected against UV rays from the sun. Therefore lighter ethnic groups are more likely to have damaged skin compared to darker ethnic groups, and the main driver of this is the number of melanocytes produced by the skin. Rawlings (2006: 87) even writes that “Overall I would expect less signs of aging, i.e. maintenance of skin elasticity in darker skinned individuals [Negroids are reported to have an intrinsic sun protection factor (SPF) value of approximately 13].”
Rawlings also writes (pg 89):
In African Americans photoaging appears primarily in lighter complexioned individuals and usually does not appear until the late fifth or sixth decade of life.
There is another factor when it comes to skin: sweat glans. I have covered in the past the fact that Asians have fewer apocrine sweat glands than whites and blacks, while blacks produce more chloride in their sweat compared to whites. Prokop-Prigge et al (2017) state “that an individual’s ethnicity has a significant impact on human axillary odor production.” Blacks also have around 70 percent more lipids in their hair, while having larger sebaceous glands than whites.
So skin color dictates numerous changes in the skin which are associated with aging. Skin aging is associated with lighter-skin, whereas hyperpigmentation is associated with darker skin. Asians have lower TEWL, highest water content, and highest skin color lipid levels while the opposite is seen for blacks. Blacks have greater gland pore size, and increased apocrine and apoeccrine sweat glands along with greater sebum excretion. White skin has an earlier onset of aging, skin wrinkling and loss of elasticity. So there are differences in ethnic skin color and structure and function, and this causes the differences we notice between ethnies and how they age.
Campiche et al (2019) write:
There is differential manifestation of aging signs in different ethnic groups.
Our results show that Africans from the African continent show delayed signs of aging compared to Caucasians.
They found no differences in forehead wrinkles between Caucasians and Africans, though there was a difference in depth of forehead wrinkles. Blacks showed less advanced crow’s feet than whites, while also having less depth. There were no differences in mouth frown lines with the exception of depth and wrinkle surface and volume parameter, of which there was an increase in Caucasian subjects compared to African subjects. Though when it comes to the length, surface and vertical lines in African subjects they showed more advanced aging but there was no difference in depth between the races. Caucasians had bigger nasiolabial folds (smile or laugh lines) than Africans, regarding length, surface, depth and volume. Africans had deeper pores than Caucasians. Africans had a greater homogeneity than Caucasians when it came to skin color. (Note that the cohorts came from France and Mauritius.)
Campiche et al (2019: 12) write:
This is also in line with the fact that photoaging in African Americans does not appear until the late fifth or sixth decade of life.22 This may explain why aging in our Black African cohort from Mauritius is less pronounced than in the Caucasian cohort although the Black African cohort is older.
The difference in age between our Caucasian and Black African cohorts (median age 46 years vs 56 years) could bring into question the comparisons of the two cohorts. Nevertheless, we mostly found that Caucasians displayed more severe signs of aging than Black Africans which is in line with the common understanding that the onset of aging in fair skin starts earlier than in darkly pigmented skin and that there were differences in the appearance of lip lines and facial pores.
So differences between the two ethnic groups come down to facial site, and measurement parameter. This study further buttresses the point that, at least when it comes to certain ethnic groups, whites age faster than blacks—even when the whites are younger than blacks (46 compared to 56 years, respectively).
When it comes to skin color and desirability, though, we see something else: light skin being prized, whereas dark skin is shunned. Jablonski (2010: 188) writes:
As we have seen, for much of recent history and around the world, pale skin has been prized to such a degree that people have been willing to risk illness and disfugurement to obtain it.
[and also on pg 177]
Preferences for light skin have arisen independently in many cultures, and they have been reinforced when different “cultures of lightness” have come into contact. Because having lighter skin has often been associated with higher social status, success, and happiness, people over the ages have sought to become lighter by various means.
I won’t ruminate on the causes of this, I just wanted to make a note of it at the end of this piece on black and white skin color.
In sum, there are many interesting differences between black and white—and even Asian—skin. Better understanding of these kinds of differences will lead to better skin care for all races, and dermatologists can then use that information to give better case based on race/ethnicity/skin color to a certain individual. We know what causes differences in skin color between individuals and groups—melanocytes. We also know that skin color and UVB radiation are strongly related. We know that there are numerous differences in skin biology when comparing different peoples whose ancestors have evolved in different climates. So understanding these differences can and will lead to better healthcare for all populations.