Skin color, like hair color, is due largely to the presence or absence of pigment produced by epidermal melanocytes. The amount of pigment synthesized by these cells is influenced by a variety of factors.
Genetic Factors
Each person inherits genes for the production of melanin. Those whose genes cause a relatively large amount of pigment to be produced have dark skins, while those whose genes cause less pigment to be formed have lighter complexions. Still others inherit mutant genes, and their cells are unable to manufacture melanin. As a consequence, their skins remain non-pigmented, and they are termed albinos.
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Environmental Factors
Environmental factors such as sunlight, ultraviolet light from sunlamps, or X rays can affect skin color by causing melanin to darken and by stimulating epidermal melanocytes to produce more pigment. This is why sun-bathing results in skin tanning. Unless the exposure to sunlight is continued, however, the tan is eventually lost, as pigmented epidermal cells become keratinized and are worn away.
Blood in the dermal vessels causes additional skin color. For example, when the blood is well oxygenated, the blood pigment hemoglobin is bright red, making the skins of light-complexioned persons and albinos appear pinkish. On the other hand, when the blood oxygen concentration is low, hemoglobin is dark red and the skin appears bluish—a condition called cyanosis.
The state of the blood vessels also has an effect on skin color. If the vessels are dilated, more blood enters the dermis, and the skin becomes redder than usual. This may happen when a person is overheated, embarrassed, or under the influence of alcohol. Conversely, conditions that produce blood vessel constriction cause blanching of the skin. Thus, if the body temperature is dropping abnormally or if a person is frightened, the skin may appear pale.
The presence of a yellow-orange plant pigment called carotene, which is especially common in yellow vegetables, may cause the skin to have a yellowish color, since it accumulates in the adipose tissue of the subcutaneous layer.
Various diseases may affect skin color. In certain forms of liver disease, bile pigments may occur in the skin and cause it to appear yellowish. A person with anemia may have pale skin due to a decrease in the concentrations of hemoglobin in blood cells.
Some middle-aged and older people have a chronic skin disorder called acne rosacea. This condition is characterized by redness of the nose, cheeks, chin, and forehead that results from persistently dilated dermal blood vessels. It is sometimes accompanied by eruptions similar to those associated with adolescent acne. Although acne rosacea seems to be inherited, the problem may be aggravated by certain foods and beverages, including alcohol.
Hormone imbalance is a common cause of skin problems. In women, it can lead to acne, hair loss, and irregular periods. In men, it can cause acne, enlarged prostate, and reduced testosterone levels. Read more here here
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