Melanin and Skin Color

Melanin

Produced in vesicles called Melanosomes, in melanocytes in the stratum basale

The enzyme Tyrosinase joins 2 molecules of the amino acid tyrosine to form melanin

Melanosomes migrate to the tips of the melanocyte and are taken into the keratinocyte by phagocytosis

Melanin is transported to the area superficial to the nucleus, where it shields the DNA from UV radiation, although it is not complete protection

Melanin degrades after a few days, so it must be replaced

Melanin effects

Melanin synthesis increases on exposure to UV radiation

Immediate Effects: Oxidize the melanin, which darken

Secondary Effects: Damage DNA of melanocytes, which increases melanin production

Melanin also decreases the synthesis of vitamin D to control the amount and keep it within a specific range

Individuals living in Africa have darker skin to prevent excess vitamin D production, while people in northern Europe have lighter skin to synthesize more vitamin D

Common Variations of Pigmentation

freckles, moles, albinism

Freckle

Small area of increased melanin production in a local spot

Mole (Nevus)

Area of increased pigmentation, caused by local proliferation of melanocytes

Albinism

Melanocytes fail to manufacture tyrosinase

Results in lack of skin pigmentation and greatly increased the risk of keratinocyte DNA damage from UV radiation

Tanning

Tanning is a $5-billion-a-year business in United States

alone where salons promote the notion of a “healthy tan”

But is there such a thing as a healthy tan?

While UVA rays are linked with tanning and UVB rays are

linked with burning, the mechanism of increased melanin

production is the same for both types of rays—oxidative

damage to existing melanin and DNA damage to

melanocytes that can lead to skin cancer

Any amount of tanning damages melanocytes and other

skin elements, ages skin prematurely, and increases risk

of skin cancer

Carotene

Yellow-orange pigment ingested in egg yolks, and yellow and orange vegetables that accumulates in the stratum corneum

Imparts a slight yellow-orange color to the skin

Particularly visible in thick skin

Hemoglobin

Iron-containing protein in red blood cells that gives blood its red color

Blood resides in the dermis, which is highly vascularized

In fair-skinned individuals, the epidermis is partly translucent, so the skin has a pinkish hue

Skin Color as a Diagnostic Tool

Blood flow to the dermis, and oxygen levels within that blood, affect skin color

ex. erythema, pallor, cyanosis, bilirubin, jaundice

Erythema

Increased blood flow to the dermis to remove heat or during injury

Appears bright red in fair-skinned individuals and as darker or lighter areas in dark-skinned individuals

Pallor

Decreased blood flow to the dermis to remove heat

In severe cases, collagen is visible

Appears white and is especially visible in fair-skinned individuals

Cyanosis

Low amounts of oxygen are in the blood from breathing difficulties, low red blood cell numbers, or if hemoglobin is unable to bind oxygen

Appears bluish in fair-skinned individuals, and bluish in the lips, gums, and nail beds in dark-skinned individual

Bilirubin

Breakdown product of red blood cells, which may build up in the blood in certain conditions and cause Jaundice

Jaundice

Appears yellow-orange in the skin and the whites of the eyes