Skin Color

Skin Pigmentation

The keratinocytes are not the only cells in the epidermis.

The melanocytes of the epidermis are crucial in determining skin pigmentation (color).

The distribution of melanin in the epidermis.

Melanin

There are two forms of the pigment melanin: eumelanin granules, which tend to be round and smooth and produce black and brown skin pigmentation, and phaeomelanin granules, which are more irregular in shape and which are more prominent in lighter skins, particularly in association with red hair and freckles.

These two forms of melanin are often both present together, and occur in varying proportions.

Among the most important of these cells are the melanocytes, which are found in the basal layer of the epidermis. These manufacture a special pigment called melanin, which helps to determine the hair and skin pigmentation. The pigment is made on tiny structures called melanosomes, which aggregate as granules and are delivered in small 'packages' to each basal cell by slender filaments called dendrites. One melanocyte supplies about 36 keratinocytes with melanin granules. These tiny packages of pigment sit over the nucleus - the vital centre of the cell - in every cell in the epidermis, and protect it from the harmful rays of the sun.

More about Melanin and Skin Color

The many shades of hair and skin color that we see in any group of people arise from varying proportions of the two different melanin pigments. A high proportion of eumelanin leads to darker skin and (particularly) hair color; people with lighter hair and skin color have less eumelanin and more phaeomelanin.

(Above and below) Melanins in varying proportions and concentrations.

Differences in skin color.

Eumelanin is the commoner and more dominant pigment of the two, particularly in hair. Most of the world's people have black hair, but skins that range from very fair to black.

Skin color and hair color tend to go together and may reflect our ancestors' adaptation to their environment. Scientists believe that the earliest humans originated hundreds of thousands of years ago in an area now found in the African continent. The gradual evolution of the human race continued along different lines, until there were essentially three different ancestral racial groups:

• Asian - Oriental peoples
• African - people of direct African descent.
• Caucasian - including the people of north-western Europe and also very dark-skinned Indians

Melanin production in skin varies in the three racial groups. 'Black' skins do not contain any more melanocytes than white ones do. But there are differences in the melanin granules in the differently colored skins. In black skins the granules are larger, whereas in white skins they are less obvious.

• In Asian people, the melanosomes are relatively large in size, and are distributed within the skin cells as a mixture of single and complex forms.
• In African skin the melanosomes are even larger; they are heavily pigmented and scattered singly throughout the keratinocytes.
• In white Caucasian skin the melanosomes are smaller and have less melanin; they are distributed as clumps in keratinocytes.

Although of Danish nationality, this man is of mixed Caucasian and African descent. His skin color, as well as other characteristics, result from his genetic make-up.

This Nigerian lady's 'black' skin contains heavy concentrations of eumelanin right through the epidermis.

Caucasian Skin Colors

 

 

In Caucasian skins the proportions of the two main melanin pigments, eumelanin and phaeomelanin, vary over a huge range.

This Japanese woman has pale skin despite her hair color.

Our skin color is the result our genetic inheritance.

Skin Colors - Evolution and Environment

In equatorial regions of Africa, Latin America and India, where there is a high degree of sun exposure, many of the
indigenous people have highly pigmented and thick skins that protect them from the harmful rays of the sun - very dark skin offers about 30 times more protection against the sun than pale skin does.

There is not, however, a definite relationship between skin pigmentation and the degree of exposure to sunlight. There are people with unexpected skin colors for the area in which they live. For example, the Tasmanian Australoids are dark-skinned although they live in a temperate latitude; also the pigmentation of American Indians, who are descendants of Asian peoples, is similar across the whole continent of North America. These examples are probably the result of migrations forty or fifty thousand years ago. A few thousand years ago, unknown factors triggered a great migration of people from east to west. The native peoples of central and western Europe were pushed westwards. Among these were the original Celts (people with blue eyes and very pale skins easily burnt by the sun), who eventually populated parts of Scotland and Ireland; their descendants can still be identified in those countries.

Similarly, in the last few hundred years peoples with white skins have migrated to Australia and South Africa - areas of high sunshine to which their skins are not well adapted, and among them sun damage and skin cancer rates are high.

Some skin types appear to show specific and curious adaptations to their climate. Many Scandinavian people have pale skins and light hair in winter. In the short but sunny summer, many of them tan quite markedly and quickly while their hair bleaches to almost white.

In the last few centuries, increasing ease of travel and the creation of multinational countries such as the USA have led to a wide range of different shades of skin and hair types and colors among the world's population.

Adapting to Ultraviolet (UV) Light

 

African and Indian peoples evolved heavily pigmented skins; but not all scientists are convinced that dark skin evolved only as an adaptation for protection against the sun's ultraviolet light. The bushmen of central Africa have dark skins, but live in tropical rainforest where there is little exposure to UV light.

One of the dark-skinned race that has inhabited Australasia for thousands of years. They migrated there from Polynesia, but are related to African peoples.

A child of the short Scandinavian summer, with a deep sun tan and nearly white hair.

This lady's biracial skin color and features reflect the mixed African and Caucasian background of her birthplace. Such mixtures of racial characteristics are seen increasingly frequently all over the world. 

One quarter of the world's population inhabits the Chinese region. The 'yellow' color of this lady's skin is probably due to a specific type of light absorption by the melanin in Asian skin, which can vary from very light to dark, depending on the amount of pigment.

Skin types from all around the world:

a tiny fraction of the enormous range.

  

 

 

 

Southeast Asia is one of the world's racial melting pots, with a huge range of gene mixtures giving rise to many beautiful skin colorations.

Skin appearance and skin color

When we look at skin many factors affect what we actually see, including the brightness and color of the light, the state of the skin and the basic skin color. These all combine to produce an effect that can alter dramatically.

In normal daylight, what we see is partly light reflected from the surface of the stratum corneum and partly light reflected back from the dermis through the translucent epidermis. If the stratum corneum contains adequate moisture and the dead cells (squames) have been removed, it is more translucent and reflects light more evenly, giving
the skin a 'shine'.

Model of the translucency of the skin.

If the skin is dry and covered in squames it scatters light instead of reflecting it evenly, and looks dull. (Much the same is true for hair.) If dry skin or hair is wetted with water, or better still with oil, it looks glossier because it reflects light better. This can be demonstrated very clearly on dry leather.

This also explains why moisturizers and exfoliators help skin to look healthier. They smooth down or remove the squames and help the epidermis to retain its moisture, so reflecting light better.

Changing this light reflection is a crucial part of what cosmetic products can do.

Very dark skins, with pigment throughout the epidermis, reflect less light from the dermis. But in skins with little or no pigment in the epidermis, the state of the tiny blood vessels in the dermis and the state of the dermis itself play a greater part in the 'complexion'.

Our skin is not so very different from leather: stiff and dull when dry, pliable and with a slight sheen when moist.

What we see as the actual skin color, as distinct from the condition, depends on light that is reflected by four different colored components of the skin, which are found at different levels throughout the epidermis and the dermis. These reflections combine to give us our unique skin color. They are:

melanin in the epidermis red blood cells containing oxygen in the small blood vessels of the dermis red blood cells without oxygen in the same blood vessels orange-yellow chemicals called carotenoids in the stratum corneum and the subcutaneous fat layer; these are principally responsible for the yellow tones of skin color, and are more abundant in men's skin than in women's.

Carotenoids are found in carrots.

Eating too many carrots can turn you orange!

Of these four factors, melanin is the most important in deciding skin color. The contribution of blood to the complexion color is most obvious in the cheeks, where capillaries are most numerous and closest to the surface.

Apparent skin color can change if the combination of its colored components changes. Changes like these are more
obvious if very little melanin is present, since melanin can hide most of the other colors. This is why people with very pale skins - 'porcelain' skins -can look blue if they get cold: blood that moves sluggishly carries less oxygen, and so looks bluish rather than having the bright red color that is given by full oxygenation.

Differing skin colors are due to the presence of the colored components of the skin in different proportions.

Pigmentation disorders

There are some rare congenital pigmentary disorders of skin. In one, the pigment is spread out along the otherwise invisible lines on the skin called Blaschko's lines. 

Vitiligo is a condition where there is patchy loss of pigment, usually over the hands and forearms but occasionally it is more extensive. It is possible to hide it by the skilful use of special water-resistant cosmetics.