Friday, August 14

Human skin color changes - Skin color variations

Changes and variations in human skin color
The diversity in the human skin color is the cumulative result of genetic adaptations brought about by the evolutionary processes of natural selection acting on the genetic variability of the population.

Human skin color change is determined by six genes and their several alleles. There is a big mix of combinations and a great variety in the skin tone is produced. The geographical distribution and evolutionary natural selection have influenced the genetic adaptations and random changes.

Changes in the normal skin color are due to certain biological, environmental or pathological conditions. Color changes are mostly temporary and are produced by the tanning, diseases and chemicals. Extraneous factors like the amount of β-carotene present in the epidermal and subcutaneous tissues and the level of oxygen saturation in the hemoglobin protein in the dermis also causes changes of the normal human skin color temporarily.

Melanin in skin pigment

Human skin color, tone and complexion are basically determined by the amount and types of melanin pigment present in the epidermal layer. The concentration and kind of melanin pigment contributing to human complexion is determined by the genotype (genetic makeup) of an individual.

Melanin is present in three forms namely pheomelanin, eumelanin and neuromelanin. Pheomelanin pigment imparts color changes ranging from red to yellow. Eumelanin imparts brown, dark brown and black color. The third type of melanin, neuromelanin, is present in the brain. All human beings have melanin pigment in their skin. Individuals with lighter complexion produce pheomelanin and people with dark complexion mostly produce eumelanin.

People with dark complexions may have slightly higher concentration of melanin producing cells (melanocytes). However human skin color changes are affected more by the quantity, type, size and pattern of distribution of the pigment than the melanocytes number. The color changes may be dark-black-brown when the skin pigmentation is very high. In the case of very little pigment in the epidermis, there is no coloration and the blood in the underlying blood vessels may impart a pink color. There is a varied range of complexion between these two extremes depending upon the type and quantity of melanin in the human epidermis.

Melanin pigment protects the epidermal layers and dermis from ultraviolet rays of sun which can cause skin cancer. Light colored individuals have tenfold risk of getting cancer under similar sunlight exposure when compared to individuals with darker complexion.

Melanin preserves folic acid from getting destroyed due to ultraviolet-A rays. Folic acid is very essential for fetal brain development and brain function in humans. Vitamin D is synthesized in the skin with the help of sunlight. As melanin blocks the sunlight from reaching deeper layers, it can cause vitamin D deficiency in dark-colored people, especially in higher latitudes.

Human skin color changes

Human skin complexion types

Knowing your complexion is very important in order to save yourself from skin cancer, vitamin D deficiency and also for choosing the right type of sunscreen. Thomas B. Fitzpatrick from Department of Dermatology of Harvard Medical School, developed a numerical skin typing which is now known as Fitzpatrick phototyping scale.The updated version of Fitzpatrick scale classifies the changes in the complexion into six types.
Type I
  • white or pale white, very fair
  • Type II
  • white, fair
  • Type III
  • white to olive
  • Type IV
  • moderate brown
  • Type V
  • brown
  • Type VI
  • very dark brown, black
  • People with complexion type I, II or III are prone to sunburn and have greater risk of skin cancer. People with types IV, V and VI may become deficient in vitamin D in higher latitudes.

    Evolution of changes skin color in humans

    human skin color changes
    Human skin color changes
    The common human ancestor lived in sub-Saharan Africa. They lived in regions of intense sunlight and ultraviolet radiation. The evolutionary changes of cooling mechanisms like loss of the body hair and increased efficient perspiration helped them in adapting to the environment. Early humans had dark skin pigment and fairer complexions have evolved later as genetic adaptations.

    The development of dark pigment was an adaptation for preserving folate and DNA from destruction and damage by ultraviolet radiation. The presence of high amount of melanin pigment protected them from the ill-effects of sun exposure. Change in human skin color is an example of natural selection influenced by the human migration and connected socio-geographic factors. These changes were influenced by human migration to colder geographic zones. Earlier most of the people with darker pigmentation lived within 20º of the equator and people with lighter pigmentation lived outside the 20º latitude.

    The mass migrations of people in the past five centuries has upset the evolution of epidermal pigment in humans and has brought in many changes and related problems. A certain amount of ultraviolet radiation is necessary for the dermis to produce vitamin D. People with darker skin pigment living in higher latitudes are at the risk of vitamin D deficiency, as the high concentration of melanin acts as a shield cutting off ultraviolet rays. Similarly, people with lighter skin pigmentation living in the tropical regions are in the constant risk of sunburns and cancer.

    Genetics of human skin complexions

    Complexion and color are polygenic traits. Human complexion is the result of the complex combination of a number of genes and changes in their alleles. The MC1R (melanocortin 1 receptor) gene and its changes are responsible for the type of melanin to be produced by the body. The KIT ligand (KITLG) gene and its mutant alle A326G (rs642742) gene are involved in the permanent survival, proliferation and migration of melanin producing cells.

    Agouti gene is involved in the production of agouti signalling peptide (ASIP) which acts as an inverse agonist causing changes in melanocytes to synthesize the pheomelanin instead of the eumelanin. Solute carrier family 24 member 5 (SLC24A5) gene, solute carrier family 45 member 2 (SLC45A2 or MATP) gene, TYR gene and Ser192Tyr (rs1042602) gene are some of the genes involved in the final determination of human skin color.

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    Author: Henry M. Trotter | license: public domain
    Current topic: Changes and variations in human skin color.

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