Normal Skin Color
Skin color, or pigmentation, is dependent on genetic factors. It varies among ethnic groups and even among individuals of the same group. Essentially human skin color is different shades of brown coupled with the hue imparted by blood flowing in the superficial vessels within the skin. The primary contributor of skin color is the pigment known as melanin. The quantity of melanin in the skin varies based on genetic factors and is also dependent on the degree of sun exposure. Melanin is produced by specialized pigment cells known as melanocytes. It produces and stores the melanin within small sacs inside it, depositing specific amounts of the pigment in the skin as determined by genetics or UV light exposure.
A commonly used scale for skin color was developed by the Harvard dermatologist Thomas B. Fitzpatrick and is known as the Fitzpatrick Scale. This classifies the different skin tones ranging from type I to type VI. It also describes the tendency of the skin to burn and ease at which it tans. However, this does not take problems with skin color into consideration. Abnormal lightening of the skin is known as hypopigmentation (decreased pigmentation) while darkening of the skin is known as hyperpigmentation.
Skin Color Problems
Changes leading to abnormal skin color includes :
- Whitening (hypopigmentation)
- Darkening (hyperpigmentation)
Some people are naturally fair and pale, with a pasty white complexion. This is not considered a pigmentation abnormality and is simply a matter of genetics. Whitening of the skin is a result of a loss of pigmentation. It should not be confused with pallor (paleness) due to a blood related problem.
- Vitiligo is when the depigmentation gradually occurs over time and presents as small hypopigmented spots that grow into larger patches. It more commonly affects the upper and lower limbs, the face and groin.
- Albinism is the partial or complete loss of pigmentation throughout the body due to a problem with an enzyme responsible for melanin production. The condition affects the skin over the entire body simultaneously, and also involves the eyes and hair.
- Pallor or paleness is a result of reduced blood supply to the skin or a diminished hemoglobin content in the blood. It can be a serious clinical sign especially when there is paleness of the lips, tongue, eyes, inside of the mouth and palms.
A darker skin color is also determined by genetics and in these cases it is not an abnormality with skin pigmentation. Even when it occurs gradually over time due to prolonged or harsh UV light exposure (usually from sunlight) it is a normal physiological response and not pathological. Hyperpigmentation, or increased skin pigmention, can occur with certain diseases.
- Melasma is a condition marked by the formation of hyperpigmented (dark) patches on the sun exposed areas of the skin, especially the face. The condition is more common in women.
- Endocrine disorders like Addison’s disease and Cushing’s disease.
- Acanthosis nigricans is darkening (hyperpigmentation) on the folds of the body and is associated with obesity and insulin resistance.
- Mercury poisoning of the skin is more likely to arise with the use of certain skin creams containing mercury. Along with corticosteroids and hydroquinones, mercury may be found in skin whitening creams although long term use is likely to cause darkening.
- Chronic skin diseases can present with hyperpigmentation as long standing inflammation damages the skin and normal pigmentation.
Redness of the skin is mainly due to increased blood flow. This can occur physiologically due to certain factors like heat and alcohol ingestion. Skin redness can also arise with inflammation (erythema) linked to skin conditions or systemic diseases. Redness is more pronounced in lighter skinned individuals.
- Trauma to the skin caused by mechanical or chemical injury. It can also arise with electromagnetic injury such as UV light (sunlight) or radiation.
- Photodermatitis is a condition where the skin is hypersensitive to sunlight and becomes red upon exposure. It is sometimes termed a sun allergy.
- Rosacea is a chronic inflammatory skin disorder characterized by intense redness of the skin on the face.
- Infections of the skin or subcutaneous tissue or abscess formation in the superficial tissue may all present with skin redness. Some systemic infections may present with skin redness or red skin rashes.
- Allergies may cause skin redness particularly when the allergen makes contact with the skin as is seen in allergic contact dermatitis.
Some ethnic groups may have a naturally yellow tinge to the skin. This is not considered abnormal. Yellowing of the skin particularly when it affects the ‘whites’ of the eyes (sclera) and inner lining of the mouth is more likely to be due to a disease.
- Jaundice is the accumulation of bilirubin in the skin. Bilirubin is a byproduct of the breakdown of red blood cells which is normally excreted through bile from the liver.
- Carotenemia is the build up of carotenoids in the blood due to excessive intake of fruits and vegetables with high concentrations of these compounds. The yellowing of the skin is most prominent in the palms.
- Copper poisoning is the accumulation of copper in the body due to excessive ingestion of the metal either intentionally or accidentally. Copper is an essential micronutrient but is only needed in minute amounts. Sometimes the problem may lie with an inherited disorder where the ability to expel excess copper from the body is compromised. This disorder with copper excretion is known as Wilson’s disease.
A greenish color of the skin is rare. It is never considered to be normal although it may be caused by veins that are visible through the skin as is seen with conditions like varicose veins especially on the legs. Some people have more visible veins that others, particularly on the face, hands and feet. These veins are more visible in light skinned individuals.
- Pseudomonas infection of the skin caused by bacteria like Pseudomonas aeruginosa can cause a slightly bluish-green tinge of the skin or green discoloration of an infected nail.
- Jewelry made of copper or silver, and sometimes certain low grades of gold mixed with other cheaper metals, can cause green discoloration of the skin. The metal is oxidized by acids on the skin surface to discolor the skin underneath it.
A bluish discoloration of the skin is always due to some abnormality. It mainly arises with low oxygen or hemoblogin levels. Bluish discoloration of the skin can also occur with breakdown of red blood cells just under the skin surface.
- Cyanosis is a blue to purple discoloration of the skin due to reduced hemoglobin levels – the component of red blood cells that carries oxygen. There are a number of different causes of cyanosis.
- Hematoma is a collection of blood which in this case is just under the skin surface. The blood clots and breaks down in the tissue where it accumulates usually after injury like a blow.