Humans in different geographical regions of the world and of different ethnicities display a variety of skin colors. All these skin colors are essentially some variation of the color, brown. The shade of brown that humans in a particular ethnic group possess is primarily determined by the extent of melanin pigmentation in the skin.
The blood flowing through the superficial blood vessels under the skin also contribute a pinkish hue to the skin color. It is more evident in individuals with a lighter skin color but also influences the overall tone of people with darker hues. Therefore skin color is essentially a combination of the amount of brown pigment (melanin) and the amount of blood flow in the superficial vessels of the skin.
Melanin and Skin Color
The amount of melanin pigment in the skin is mainly determined by genetic factors. Exposure to the sun also increases melanin pigmentation of the skin to some extent. The melanin pigment in the skin is synthesized by specialist pigment cells known as melanocytes. After synthesizing melanin, the melanocytes store the pigment within small sacs.
Depending on genetic factors and the amount of exposure to ultraviolet light, melanocytes deposit specific amounts of the melanin pigment in the skin. The more melanin pigment in the skin, the darker the skin color. Conversely, the less melanin pigment in the skin the lighter the skin color. Blood flow through the skin can vary depending on internal and external factors.
Discoloration of the Skin
A Harvard dermatologist named Thomas B. Fitzpatrick developed a scale to measure the skin color in humans. This scale, known as the Fitzpatrick scale, classifies human skin tones into types I to VI. The Fitzpatrick scale also describes the ease with which a particular skin type tans or burns. The Fitzpatrick scale deals with normal skin coloration in humans.
However, the scale does not describe abnormal skin coloration. Changes in skin tan could result either from decreased melanin pigmentation (technically known as hypopigmentation) or increased melanin pigmentation (technically known as hyperpigmentation). Apart from the abnormal changes in the tan, human skin could also display abnormal colors such as red, blue, green, and yellow.
White Discoloration of the Skin
People in some ethnic groups are naturally pale or possess a lighter complexion. Their pasty white complexion is an entirely normal skin color. These naturally fair-skinned individuals have genetically lower amounts of melanin in their skin. However, a pale or white skin color can also occur due to certain abnormalities.
In vitiligo, small areas of the skin gradually lose their normal pigmentation and become white. These hypopigmented skin spots gradually grow into larger patches. Vitiligo mostly affects the skin on the face, groin, upper limbs and lower limbs.
Albinism is characterized by a partial or complete loss of pigmentation from the skin in all regions of the body. The loss of pigmentation in albinism is due to a defect in the enzyme that is involved in the production of melanin. In addition to skin, albinism also affects the hair and the eyes.
Pallor refers to a pale skin that is caused by either a reduced cutaneous blood supply or a depletion of hemoglobin content in the blood. When paleness also affects the eyes, tongue, lips, mouth and palms, one must seek immediate medical attention. Pallor is not due to hypopigmentation of the skin.
Read more on paleness.
Darker Skin Discoloration
Individuals belonging to certain ethnic groups naturally possess a dark skin color. These naturally dark-skinned individuals usually live in hot climates, and have genetically higher levels of melanin pigment in their skin.
The increased amounts of melanin pigment in these ethnic groups is a genetic adaptation that allows them to survive in geographical regions where UV exposure through sunlight is high. People with fairer skin may also develop a darker skin tan upon prolonged exposure to harsh sunlight.
This is a normal physiological adaptation to the environment, and is not considered abnormal hyperpigmentation.
Melasma is characterized by the formation of hyperpigmented patches in skin areas that are exposed to the sun. The skin on the face is most commonly affected in melasma. Women are relatively more prone to suffering from melasma than men.
Certain endocrine disorders, such as Cushing’s disease and Addison’s disease, can also result in abnormal skin hyperpigmentation.
Acanthosis nigricans is associated with insulin resistance and obesity. This condition is characterized by an abnormal hyperpigmentation of skin folds in the body.
Certain skin-whitening creams may contain mercury. Long term use of such skin creams can cause an abnormal hyperpigmentation of the skin.
Chronic skin diseases
Chronic skin diseases are characterized by chronic skin inflammation. Over time, this may result in skin hyperpigmentation.
Read more on black skin fungus.
Red Discoloration of the Skin
Skin color can appear red in conditions that cause an increased cutaneous blood flow. Physiological factors that increase cutaneous blood flow include alcohol consumption and heat. Pathological causes of changes in cutaneous blood flow include inflammation and some systemic diseases. Light-skinned individuals are more likely to display a reddish skin color upon changes in cutaneous blood flow.
Chemical, mechanical, and radiation injuries to the skin can cause the affected skin area to turn red.
Also known as sun allergy, photodermatitis is characterized by the skin turning red upon exposure to sunlight. This occurs in certain individuals who are hypersensitive to sunlight.
Rosacea is a chronic inflammatory skin condition that causes the skin on the face to become red.
A red skin may also be caused by a variety of infections that affect the skin and the subcutaneous tissue. Certain systemic infections may also cause skin redness.
Skin allergies, such as allergic contact dermatitis, can also cause local skin redness.
Yellow Discoloration of the Skin
A yellow tinge in skin color may occur naturally in certain ethnic groups. However, a yellow skin (especially in conjunction with a yellowing of sclera and inner mouth) is usually caused by a disease.
Jaundice is characterized by a yellowing of the skin that is caused by accumulation of bilirubin.
Carotenemia is caused by an excessive intake of foods that are rich in carotenoids. A buildup of carotenoids in the blood may cause a yellowing of the skin (especially in the palm region).
Accumulation of copper in the body can also cause a yellow skin. Excess copper in the body could come from excessive intake of substances rich in copper. Copper accumulation in the body could also be due to inherited disorders (such as Wilson’s disease) that compromise the ability of the body to expel excess copper.
Green Discoloration of the Skin
A greenish skin color is not considered normal in any condition. Varicose veins and infections by the Pseudomonas aeruginosa bacteria can result in greenish skin areas. A localized green discoloration of the skin can also occur after wearing jewelry that is made of silver, copper and other metals. In such cases, the green color is caused by an oxidation of the metal by acids on the skin surface.
Blue Discoloration of the Skin
A bluish skin color can be caused by low oxygen or hemoglobin level in the blood. Reduced hemoglobin content can cause a condition known as cyanosis, which is characterized by bluish-purple discoloration of the skin. A bluish skin color can also be caused by an accumulation of blood (hematoma) under the skin.